Method for preparing iron-based biochar material from iron-rich biomass and application of iron-based biochar material

Abstract

The invention provides a method for preparing an iron-based biochar material by using iron-rich biomass and application of the iron-based biochar material. The method comprises the following steps: (1) cleaning iron-rich rice roots, and drying the iron-rich rice roots; and (2) sequentially shearing, grinding and sieving the dried iron-rich rice roots to obtain rice root powder. And (3) mixing the rice root powder with pure water, and adding a magnetic stirrer for stirring. And (4) sequentially drying and grinding the mixture to obtain powder to be treated. And (5) putting the to-be-treated powder into a tubular furnace, introducing nitrogen, and pyrolyzing the to-be-treated powder to obtain the iron-based biochar material at different pyrolysis temperatures. According to the method, the iron-rich biological roots abandoned after rice harvesting are used as raw materials, and recycling of abandoned biomass is achieved. According to the method, exogenous iron does not need to be added, the agglomeration phenomenon of an iron-based material is effectively relieved, and the prepared iron-based biochar can quickly remove hexavalent chromium in water and polluted soil.

Description

Technical Field

[0001] The present invention relates to the technical field of environmental protection and soil pollution remediation, and in particular to a method for preparing an iron-based biochar material by utilizing iron-rich biomass and its application. Background Art

[0002] Chromium pollution is an urgent environmental challenge in the fields of environmental protection and soil remediation. Hexavalent chromium is highly oxidizing, water-soluble, and highly mobile. Hexavalent chromium is 100 times more toxic than trivalent chromium and is classified as a Class 1 carcinogen. It can enter the human body through the food chain, posing a threat to human health. Reducing hexavalent chromium to trivalent chromium is a key challenge in the remediation of chromium-contaminated water and soil. Iron-based biochar materials have a large specific surface area, good porosity, and strong adsorption capacity. They also have strong reducing power, excellent mechanical properties, low preparation cost, and easy separation. They have strong remediation capabilities for hexavalent chromium removal and are becoming a popular remediation method. Methods for synthesizing iron-based biochar include chemical reduction, thermal conversion, hydrothermal carbonization, co-precipitation, and ball milling.

[0003] Many researchers have developed iron-based biochar materials based on iron-based materials such as zero-valent iron, iron oxide, and iron carbide, which possess both adsorption and reduction capabilities and can synergistically remove hexavalent chromium. These preparation methods all have drawbacks, such as complex processes and the potential for secondary pollution. Chemical reduction methods for preparing iron-carbon materials offer the advantages of relatively uniform iron loading and simplicity and efficiency. However, frequently used reducing agents, such as borohydrides, can easily generate toxic gases during the preparation process, causing secondary pollution. The co-precipitation method involves adding iron to pyrolyzed biochar in an iron-containing alkaline liquid and then pyrolyzing it in an inert gas. This method is simple and controllable, but is susceptible to environmental factors, resulting in lower product quality. Hydrothermal carbonization technology is more environmentally friendly, but suffers from drawbacks such as leaching and difficulty in collecting the product. Furthermore, the preparation of exogenous iron-based biochar requires optimized preparation conditions, such as the iron-to-carbon ratio, raw materials, and pyrolysis temperature. In practice, parameter optimization requires significant human and material resources, and studies have shown that exogenous iron-based biochar still suffers from aggregation, low stability, and poor long-distance migration.

[0004] Therefore, there is a need for a method for preparing iron-based biochar materials from iron-rich biomass that simplifies the preparation process of exogenous iron-based biochar materials, does not produce toxic by-products, and can solve problems such as easy aggregation and easy oxidation. Summary of the Invention

[0005] In order to overcome the problems existing in the related art, the purpose of the present invention is to provide a method and application of preparing iron-based biochar materials using iron-rich biomass, wherein the method simplifies the preparation process of exogenous iron-based biochar materials, does not produce toxic by-products, and can solve problems such as easy aggregation and easy oxidation.

[0006] A method for preparing an iron-based biochar material using iron-rich biomass comprises:

[0007] (1) cleaning the iron-rich rice roots and drying the iron-rich rice roots;

[0008] (2) chopping, grinding, and sieving the dried iron-rich rice roots in sequence to obtain rice root powder;

[0009] (3) mixing the rice root powder and pure water, adding a magnetic stirrer to stir, and obtaining a mixture;

[0010] (4) drying and grinding the mixture in sequence to obtain a powder to be processed;

[0011] (5) The powder to be treated is placed in a tubular furnace and nitrogen is introduced, and the pyrolysis temperature is gradually increased from room temperature to 900°C to pyrolyze the powder to be treated to obtain iron-based biochar materials at different pyrolysis temperatures; wherein the iron-based biochar materials are used to remove hexavalent chromium in water and soil.

[0012] In a preferred technical solution of the present invention, the mixing ratio of rice root powder and pure water in step (3) is 3g:100mL, the stirring temperature is 50°C, the stirring speed is 800-1200rpm, and the stirring time is 2h.

[0013] In a preferred technical solution of the present invention, the pyrolysis temperature in step (5) is gradually increased from room temperature to 300°C, 500°C, 700°C and 900°C at 10°C / min.

[0014] In a preferred technical solution of the present invention, the gas flow rate in step (5) is 50 mL / min and the pyrolysis time is 2 h.

[0015] In a preferred technical solution of the present invention, the iron-rich rice root is the root of indica rice or japonica rice, the indica rice variety includes Huayou 86, and the japonica rice variety includes Nanjing 9108.

[0016] In a preferred technical solution of the present invention, the iron content of the root of the iron-rich rice is greater than or equal to 1%.

[0017] In a preferred technical solution of the present invention, step (6) is also included: nitrogen doping the iron-based biochar material to improve the performance of the iron-based biochar material in a high pH system.

[0018] In a preferred technical solution of the present invention, nitrogen doping selects N chemical reagents or biopolymers with different nitrogen contents as nitrogen precursors, wherein 1≤N≤6; the chemical reagents include urea, ammonium nitrate and melamine, and the biopolymers include peptone, yeast powder and nitrogen-rich algae biomass.

[0019] In a preferred technical solution of the present invention, in step (6), 10 g of rice root powder is mixed with 500 mL of methanol and ultrasonically treated at 70% intensity for 30 minutes. 20 g, 10 g, 5 g and 3.33 g of nitrogen precursor are added to the suspension so that the addition ratio of nitrogen precursor to rice root powder is 2:1, 1:1, 1:2 and 1:3, respectively. The suspension is heated at 80°C for 8 hours to volatilize the methanol solvent.

[0020] The present invention also provides an application of a method for preparing an iron-based biochar material using iron-rich biomass in removing hexavalent chromium from water and contaminated soil.

[0021] The beneficial effects of the present invention are:

[0022] The present invention provides a method for preparing an iron-based biochar material using iron-rich biomass, comprising: (1) washing iron-rich rice roots and drying the iron-rich rice roots. The iron-rich rice roots are common indica rice and japonica rice varieties, and the soil and impurities on the surface of the iron-rich rice roots are washed with water. The iron-rich rice roots are dried by a blower or an automatic drying method. (2) The dried iron-rich rice roots are chopped, ground and sieved in sequence to obtain rice root powder, which is uniform and has a high specific surface area. (3) The rice root powder is mixed with pure water, and a magnetic stirrer is added for stirring to further wash away impurities and alkali metals on the surface of the rice root powder to obtain a mixture. (4) The mixture is dried and ground in sequence to obtain a powder to be treated. (5) The powder to be treated is placed in a tubular furnace and nitrogen is introduced. The pyrolysis temperature is gradually increased from room temperature to 900°C to pyrolyze the powder to be treated to obtain iron-based biochar materials at different pyrolysis temperatures. The present invention uses iron-rich biological roots discarded after rice harvest as raw materials. The raw materials are widely available, easy to obtain in large quantities, and low in cost, thus realizing the reuse of waste biomass. The present invention uses a direct one-step pyrolysis method of iron-rich rice roots to prepare iron-based biochar materials. The iron-based biochar materials are iron-carbon materials with endogenous iron and do not require the addition of exogenous iron. Since the endogenous iron is evenly distributed on the surface and inside of the raw biomass, the zero-valent iron generated by the in-situ reaction is evenly loaded in the iron-based biochar, effectively alleviating the agglomeration phenomenon of the iron-based material. The iron-based biochar prepared by the present invention can quickly remove hexavalent chromium from water within 1 hour. The removal capacity of hexavalent chromium per unit mass of iron in the material is much greater than that of nano zero-valent iron and iron-based biochar materials with exogenous iron addition, and the iron-based biochar removes hexavalent chromium in water bodies mainly by reduction. When treating contaminated soil, after 10 days of remediation treatment, the leaching toxicity of hexavalent chromium in the contaminated soil reaches the Class II standard of groundwater quality standards, and the effective chromium concentration in the soil is lower than the risk screening value for agricultural land. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Figures 2 and 3 are SEM images of the iron-based biochars of the present invention at different temperatures. Figures 2 and 3 are SEM images of BC300, BC500, BC700, and BC900, respectively, with magnifications of 1 μm and 100 nm.

[0024] Figure 2 Figures 2 and 3 are the mapping diagrams of the iron-based biochars at different temperatures of the present invention. Figures 2 and 3 are the mapping diagrams of BC300, BC500, BC700 and BC900, respectively, with magnifications of 1 μm and 100 nm.

[0025] Figure 3 1 is the XRD pattern of the iron-based biochar of the present invention at different temperatures;

[0026] Figure 4FTIR images of the iron-based biochar of the present invention at different temperatures;

[0027] Figure 5 This is a result diagram showing the effect of different pH values on the Cr(VI) removal rate of the material according to the present invention;

[0028] Figure 6 This is a result diagram of the removal capacity of Cr(VI) per unit mass of iron of the material under different pH conditions of the present invention;

[0029] Figure 7 Result diagram of Cr(VI) removal rate of materials under different conditions of the present invention;

[0030] Figure 8 This is a result diagram of the removal capacity of Cr(VI) per unit mass of iron of the material under different pH conditions of the present invention;

[0031] Figure 9 The figures are the result of the concentration change of Cr(VI) removal by the present invention, wherein (a) is the concentration change of Cr(VI) removed by BC900; (b) is the concentration change of Cr(VI) when 0, 5, 10 and 15 mM 1,10-phenanthroline inhibits the action of Fe(II); (c) is the concentration change of dissolved iron in the system when no Cr(VI) is added; (d) is the concentration change of dissolved iron in the system when Cr(VI) is added;

[0032] Figure 10 is a schematic diagram of the Cr(VI) removal contribution of the present invention;

[0033] Figure 11 This is a graph showing the concentration change of Cr(VI) in water removed by BC900 of the present invention;

[0034] Figure 12 This is a graph showing changes in the content of available chromium during the process of repairing chromium-contaminated soil using BC900 of the present invention;

[0035] Figure 13 This is a graph showing the concentration change of Cr(VI) leaching toxicity during the process of repairing chromium-contaminated soil using BC900 of the present invention;

[0036] Figure 14 This is a graph showing the concentration change of Cr leaching toxicity during the process of repairing chromium-contaminated soil using BC900 of the present invention. DETAILED DESCRIPTION

[0037] The preferred embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Although preferred embodiments of the present invention are shown in the accompanying drawings, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. Rather, these embodiments are provided to make the present invention more thorough and complete and to fully convey the scope of the present invention to those skilled in the art.

[0038] Example 1

[0039] like Figure 1 As shown, this embodiment provides a method for preparing an iron-based biochar material using iron-rich biomass, comprising:

[0040] (1) cleaning the iron-rich rice roots and drying the iron-rich rice roots;

[0041] (2) chopping, grinding, and sieving the dried iron-rich rice roots to obtain rice root powder;

[0042] (3) mixing the rice root powder and pure water, adding a magnetic stirrer to stir, and obtaining a mixture;

[0043] (4) drying and grinding the mixture in sequence to obtain a powder to be processed;

[0044] (5) The powder to be treated is placed in a tubular furnace and nitrogen is introduced, and the pyrolysis temperature is gradually increased from room temperature to 900°C to pyrolyze the powder to be treated to obtain iron-based biochar materials at different pyrolysis temperatures; wherein the iron-based biochar materials are used to remove hexavalent chromium in water and soil.

[0045] The iron-rich rice roots have an iron content greater than or equal to 1%. The first approach involves using rice plants that are at least two months old, with a root iron content of 1%-2%. The second approach involves using mature rice plants, with a root iron content greater than 2%. The iron-rich rice roots are roots of indica or japonica rice. Indica rice varieties include Huayou 86, and japonica rice varieties include Nanjing 9108. Roots of other indica and japonica rice varieties may also be used, without limitation.

[0046] During the cleaning process of step (1), the soil and impurities on the surface of the iron-rich rice roots are cleaned with water, and the cleaning is repeated until the cleaning liquid is clear. The roots are then dried in a forced air oven at 70°C or air-dried in a natural state. During the processing of the iron-rich rice roots in step (2), the iron-rich rice roots are initially chopped using ceramic scissors, and then the iron-rich rice roots are ground using a high-speed grinder at a speed of 30,000 r / min. The ground rice root powder is screened using a 100-mesh screen to screen out a uniform rice root powder with a high specific surface area.

[0047] In step (3), the mixing ratio of rice root powder and pure water is 3 g:100 mL, a magnetic stirrer is added, a water bath is heated to 50° C., and stirred at a speed of 800-1200 rpm for 2 h to further wash away impurities and alkali metals on the surface of the rice root powder.

[0048] In step (4), the mixture is filtered and dried at 70°C, and the dried powder is ground to obtain a powder to be treated. In step (5), the powder to be treated is placed in a tube furnace, and nitrogen is introduced to pyrolyze the powder to be treated. At room temperature, i.e., 25°C, the temperature is gradually increased to 300°C, 500°C, 700°C, and 900°C at a rate of 10°C / min. The gas flow rate is 50 mL / min, the pyrolysis time is 2 hours, and the obtained biochar materials are recorded as BC300, BC500, BC700, and BC900. The four obtained iron-based biochar materials are stored in a vacuum drying oven for standby use, wherein BC300 is an iron-based biochar material obtained by pyrolysis at 300°C, BC500 is an iron-based biochar material obtained by pyrolysis at 500°C, BC700 is an iron-based biochar material obtained by pyrolysis at 700°C, and BC900 is an iron-based biochar material obtained by pyrolysis at 900°C.

[0049] The use of a 100-mesh sieve in step (2) can make the raw material particles uniform and have a large specific surface area, while preventing agglomeration of excessively fine powders. The mixing ratio of rice root powder and pure water in step (3) is 3g:100mL, which can avoid uneven stirring caused by excessively thick suspension or low suspension viscosity.

[0050] The present embodiment provides a method for preparing an iron-based biochar material using iron-rich biomass, comprising: (1) washing iron-rich rice roots and drying the iron-rich rice roots. The iron-rich rice roots are common indica and japonica rice varieties. The soil and impurities on the surface of the iron-rich rice roots are washed with water, and the iron-rich rice roots are dried by a blower or automatic drying method. The dried iron-rich rice roots are chopped, ground, and sieved in sequence to obtain rice root powder. The rice root powder is uniform and has a high specific surface area. The rice root powder is mixed with pure water, and a magnetic stirrer is added for stirring to further wash away impurities and alkali metals on the surface of the rice root powder to obtain a mixture. The mixture is dried and ground in sequence to obtain a powder to be treated. The powder to be treated is placed in a tubular furnace and nitrogen is introduced. The pyrolysis temperature is gradually increased from room temperature to 900°C to pyrolyze the powder to be treated to obtain iron-based biochar materials at different pyrolysis temperatures. The present invention uses iron-rich biological roots discarded after rice harvest as raw materials. The raw materials are widely available, easy to obtain in large quantities, and low in cost, thus realizing the reuse of waste biomass. The present invention uses a direct one-step pyrolysis method of iron-rich rice roots to prepare iron-based biochar materials. The iron-based biochar materials are iron-carbon materials with endogenous iron and do not require the addition of exogenous iron. Since the endogenous iron is evenly distributed on the surface and inside of the raw biomass, the zero-valent iron generated by the in-situ reaction is evenly loaded in the iron-based biochar, effectively alleviating the agglomeration phenomenon of the iron-based material. The iron-based biochar prepared by the present invention can quickly remove hexavalent chromium from water within 1 hour. The removal capacity of hexavalent chromium per unit mass of iron in the material is much greater than that of nano zero-valent iron and iron-based biochar materials with exogenous iron addition, and the iron-based biochar removes hexavalent chromium in water bodies mainly by reduction. When treating contaminated soil, after 10 days of remediation treatment, the leaching toxicity of hexavalent chromium in the contaminated soil reaches the Class II standard of groundwater quality standards, and the effective chromium concentration in the soil is lower than the risk screening value for agricultural land.

[0051] Example 2

[0052] This embodiment provides a method for preparing an iron-based biochar material using iron-rich biomass, comprising:

[0053] (1) cleaning the iron-rich rice roots and drying the iron-rich rice roots;

[0054] (2) chopping, grinding, and sieving the dried iron-rich rice roots in sequence to obtain rice root powder;

[0055] (3) mixing the rice root powder and pure water, adding a magnetic stirrer to stir, and obtaining a mixture;

[0056] (4) drying and grinding the mixture in sequence to obtain a powder to be processed;

[0057] (5) The powder to be treated is placed in a tubular furnace and nitrogen is introduced, and the pyrolysis temperature is gradually increased from room temperature to 900°C to pyrolyze the powder to be treated to obtain iron-based biochar materials at different pyrolysis temperatures; wherein the iron-based biochar materials are used to remove hexavalent chromium in water and soil.

[0058] The method further comprises the step (6): nitrogen doping the iron-based biochar material to improve the performance of the iron-based biochar material in a high pH system.

[0059] Nitrogen doping selects N chemical reagents or biopolymers with different nitrogen contents as nitrogen precursors, where 1≤N≤6; the chemical reagents include urea, ammonium nitrate and melamine, and the biopolymers include peptone, yeast powder and nitrogen-rich algae biomass.

[0060] The application of iron-based materials is largely limited by pH. To further expand the pH range of these materials, iron-based biochar can be further doped with nitrogen to modify its properties, thereby improving its performance in high-pH environments. Nitrogen doping can enhance the biochar's adsorption capacity for hexavalent chromium ions by reducing its surface electronegativity. This, in turn, promotes the formation of persistent free radicals in the biochar, which can synergistically reduce and remove hexavalent chromium ions with iron.

[0061] The ground powder was sieved through a 100-mesh sieve to obtain rice root powder. The rice root powder was mixed with pure water and stirred with a magnetic stirrer to further wash away impurities and alkali metals on the surface of the rice root powder to obtain a mixture, thereby reducing the ash and mineral content in the rice root powder as much as possible. Six typical chemical reagents or biopolymers with different nitrogen contents were selected as nitrogen precursors, such as urea, ammonium nitrate, melamine, peptone, yeast powder and nitrogen-rich algae biomass. The nitrogen content of urea is 46.67%, the nitrogen content of ammonium nitrate is 35%, the nitrogen content of melamine is 66.67%, the nitrogen content of peptone is higher than 10.5%, the nitrogen content of yeast powder is higher than 9%, and the nitrogen content of nitrogen-rich algae biomass is higher than 40%. The nitrogen-rich algae biomass needs to be washed three times with 0.1M HCl to eliminate the significant influence of inherent ash.

[0062] 10g of rice root powder was mixed with 500mL of methanol and sonicated at 70% intensity for 30 minutes. 20g, 10g, 5g, and 3.33g of nitrogen precursors were added to the suspension. The nitrogen precursors were any one of urea, ammonium nitrate, melamine, peptone, yeast powder, and nitrogen-rich algal biomass, so that the nitrogen precursor to rice root powder addition ratios were 2:1, 1:1, 1:2, and 1:3, respectively. The mixture was heated at 80°C for 8 hours to completely evaporate the methanol solvent. The above steps were repeated three times to ensure that the rice root powder and nitrogen precursors were thoroughly mixed. The dried mixture was ground and sieved again using a 100-mesh sieve to obtain a powder to be treated.

[0063] The treated powder was placed in a tubular furnace and pyrolyzed with nitrogen. The temperature was gradually increased from room temperature (25°C) to 300°C, 500°C, 700°C, and 900°C at a rate of 10°C / min, with a gas flow rate of 50 mL / min. The pyrolysis times were set to 0.5 h, 1 h, and 2 h, respectively. As a control, pristine biochar with the addition of a nitrogen precursor was simultaneously prepared using the above steps.

[0064] This embodiment also includes step (6): nitrogen doping of the iron-based biochar material to improve the performance of the iron-based biochar material in a high pH system. The nitrogen doping comprises selecting N chemical reagents or biopolymers with different nitrogen contents as nitrogen precursors, wherein 1≤N≤6; the chemical reagents include urea, ammonium nitrate and melamine, and the biopolymers include peptone, yeast powder and nitrogen-rich algae biomass. In step (6), 10g of rice root powder is mixed with 500mL of methanol, ultrasonically treated at 70% intensity for 30min, and 20g, 10g, 5g and 3.33g of nitrogen precursor are added to the suspension so that the addition ratio of nitrogen precursor to rice root powder is 2:1, 1:1, 1:2 and 1:3 respectively, and heated at 80℃ for 8 hours to volatilize the methanol solvent. The application of iron-based materials is largely limited by pH. To further expand the pH range of these materials, iron-based biochar can be further doped with nitrogen to modify its properties, thereby improving its performance in high-pH environments. Nitrogen doping can enhance the biochar's adsorption capacity for hexavalent chromium ions by reducing its surface electronegativity. This, in turn, promotes the formation of persistent free radicals in the biochar, which can synergistically reduce and remove hexavalent chromium ions with iron.

[0065] Example 3

[0066] This example uses field-emission scanning electron microscopy to observe the surface morphology and microstructure of the iron-based biochar. Furthermore, a combination of SEM (scanning electron microscopy) and EDS (energy dispersive X-ray spectroscopy) was used to characterize the microscopic distribution and binding morphology of Fe, C, and O elements within the iron-based biochar. Prior to SEM observation, the freeze-dried sample was gold-sprayed under vacuum to enhance its conductivity.

[0067] like Figure 1 and Figure 2 As shown in Figures (a) and (b) of BC300, (c) of BC500, and (d) of BC900. The SEM images show that as the pyrolysis temperature increases, for example, from 300°C to 900°C, the biochar surface gradually transforms from a rugged, rough structure (e.g., BC300 and BC500) to a dense, smooth structure (e.g., BC700 and BC900). High-temperature calcination of the iron-based biochar material BC900 reveals significant structural fragmentation and pore collapse. The carbon layers of BC900 likely undergo an ordered rearrangement, gradually forming a layered structure similar to graphite. BC500 exhibits sporadic 0.5 μm macropores, while BC300 and BC500 lack a distinct pore structure.

[0068] At a scale of 100nm, the SEM image shows that spherical particles are attached to the surface of the iron-based biochar material, and as the temperature increases, the particle morphology tends to be regular and evenly distributed. EDS iron element analysis shows that the iron-based biochar materials prepared at the four temperatures all have significant iron enrichment, confirming that the present invention can successfully prepare iron-carbon materials with endogenous iron without the need to add exogenous iron. The iron signal intensity distribution in the mapping diagram is uniform, indicating that the iron is relatively evenly distributed on the surface of the iron-based biochar material, effectively alleviating the agglomeration of the iron-based material.

[0069] Furthermore, combined with SEM morphology analysis, the iron fluorescence signal intensity in the spherical regions of BC700 and BC900 particles was higher than that in the substrate, suggesting that the spherical particles are iron-carbon complexes. An elemental analyzer was used to determine the percentages of C, H, N, and S in the raw materials and iron-based biochar, and ICP-MS was used to analyze the Fe element. A 100 mg sample of rice root powder was weighed, added to 10 mL of high-purity water, and thoroughly mixed and shaken for 1 hour. The pH of the reaction solution was measured using a pH meter, and two control groups were set up.

[0070] Table 1 shows the elemental composition analysis of the original iron-rich rice roots and iron-based biochar materials at different temperatures. The iron content of the materials increases with the increase of pyrolysis temperature. The iron content of the iron-based biochar materials increases from the original 1.82% to 5.63%, 7.08%, 8.96% and 11.01%, respectively, with a maximum increase of 9.18%, which once again proves that the present invention successfully synthesizes iron-based biochar materials using biomass with endogenous iron. The fired iron-based biochar materials are mainly composed of C, H, N and O. Compared with the original materials, as the temperature increases, the C content increases, the H content decreases, and the N content does not change much. The hydrogen-carbon ratio of the iron-based biochar material can reflect the degree of aromatization and carbonization stability of the iron-based biochar material. The hydrogen-carbon ratio gradually decreases with the increase of temperature, indicating that the dehydrogenation and deoxygenation reactions are intensified, and the unstable aliphatic carbon is transformed into a highly condensed aromatic ring structure. The aromatization degree of the biochar is enhanced and the carbon skeleton tends to be stable. The pH value of iron-based biochar increased with increasing pyrolysis temperature, which may be caused by the hydrolysis of alkali and alkaline earth metal salts such as Ca, Mg, Na, and K. The yield of iron-based biochar decreased with increasing temperature, which may be due to the vigorous decomposition of hemicellulose, cellulose, and organic components under high-temperature pyrolysis conditions, releasing CO2 and volatilization of tar and other components.

[0071] This example analyzes the elements, pH and yield of iron-based biochar at different temperatures. The iron content of the material increases with the increase of pyrolysis temperature. The iron content of the iron-based biochar material increases from the original 1.82% to 5.63%, 7.08%, 8.96% and 11.01%, respectively, with a maximum increase of 9.18%, which once again proves that the present invention successfully synthesizes iron-based biochar materials using biomass with endogenous iron. The fired iron-based biochar material is mainly composed of C, H, N and O. Compared with the original material, as the temperature increases, the C content increases, the H content decreases, and the N content does not change much. The hydrogen-carbon ratio of the iron-based biochar material can reflect the degree of aromatization and carbonization stability of the iron-based biochar material. The hydrogen-carbon ratio gradually decreases with the increase of temperature, indicating that the dehydrogenation and deoxygenation reactions intensify, and the unstable aliphatic carbon transforms into a highly condensed aromatic ring structure. The aromatization degree of the biochar is enhanced and the carbon skeleton tends to be stable.

[0072] Table 1 Elemental composition, pH and yield of different materials

[0073]

[0074] Example 4

[0075] In this example, after the iron-based biochar particles were ground into powder using an agate mortar, the mineral crystal form of the iron-based biochar material was determined by X-ray diffraction analysis at a diffraction angle of 5–90° and a rate of 5° / min. The XRD spectrum was then analyzed using MID Jade 6.5 software.

[0076] Figure 3 The XRD patterns of biochar at different temperatures are used to analyze the composition of iron-based biochar materials. The experimental results show that BC900 has a graphitized carbon peak at 2θ = 60° (103) crystal planes, indicating that as the temperature increases, the carbon layer forms a graphite-like layered structure through polycondensation, which is consistent with the results of SEM morphology observations.

[0077] Different forms of iron were formed by pyrolysis at different temperatures. Under low temperature conditions, BC300 formed Fe2O3 with (110) crystal plane at 2θ=44.67°. Under medium temperature conditions, BC700 and BC500 mainly formed Fe3O4 (2θ=44.67°(220), 65.02°(311), 65.02°(400), 82.33°(440)). Under high temperature conditions, BC900 showed obvious Fe with (110), (200) and (211) crystal planes at 2θ=44.67°, 65.02° and 82.33°. 0 , indicating that the present invention has successfully prepared a zero-valent iron-based biochar composite material. Combined with the SEM image of BC900, it was found that the iron-carbon spherical composite material is much smaller than 100nm, indicating that the iron base prepared is nano-zero-valent iron (nZVI). As the temperature increases, it can be observed that the characteristic peak intensity of Fe2O3 and Fe3O4 gradually weakens, and Fe 0 The peak appears, and it can be seen that the iron oxide is moving towards Fe 0 Under low temperature conditions, the pyrolysis products are mainly low-crystalline hematite (Fe2O3), which is further transformed into crystalline magnetite (Fe3O4), wollastonite (FeO) and zero-valent iron (Fe 0 ), the reaction process is shown in equations (1), (2) and (3). SiO2 with the same crystal plane appears under all temperature conditions. As a silicon-loving plant, the silicon in rice is mainly polymeric silicon and water-soluble silicic acid. Polymeric silicon and water-soluble silicic acid exist in the form of silicon phytosomes, with a content of up to 35%–38% of the dry weight, which plays a role in providing nutrition and protecting the plant body. During the pyrolysis process, silicon and carbon interact with each other, with carbon protecting silicon from dissolution and silicon protecting carbon from loss, thus forming a stable biochar material with a certain degree of anti-degradation ability. At higher pyrolysis temperatures, the silicon ash is transformed from an amorphous state to nano-SiO2 crystalline particles.

[0078] 6Fe2O3+≡C→4Fe3O4+CO2↑(1)

[0079] 2Fe3O4+≡C→6FeO+CO2↑(2)

[0080] 2FeO+≡C→2Fe+CO2↑(3)

[0081] Fourier transform infrared spectroscopy was used to analyze the organic functional groups on the surface of the iron-based biochar powder samples. The wavelength range of the selected infrared spectrum was 4000 to 400 cm -1 Before FTIR analysis, the powder sample was mixed with IR-dried KBr powder at a weight ratio of 1:100 and then pressed into pellets.

[0082] Figure 4 The FTIR qualitative analysis spectra of the surface functional groups of biochar at different pyrolysis temperatures show that the peak intensity of the organic functional groups decreases and the number of peaks decreases with increasing temperature. The biochar at all pyrolysis temperatures has the peaks at 3426.8, 1612.6, 1081.3, 791.7, 541.7 and 464.9 cm -1 The absorption peaks are mainly derived from hydroxyl (C-OH), carbon-carbon double bond (C=C), alcoholic hydroxyl, phenolic hydroxyl, carboxyl (CO), SiO2 (Si-O-Si) and Fe3O4 (Fe-O). The intensity of these peaks decreases with the increase of pyrolysis temperature. When the temperature is greater than or equal to 500℃, the peaks at 1706.7 and 2935.0 cm -1 The functional groups at the positions disappear, which correspond to the carbonyl groups in dimerized saturated fatty acids and the CH bonds and C-H2 in aliphatic hydrocarbons, respectively.

[0083] This phenomenon indicates that high temperature significantly reduces the organic functional groups in biochar, which is attributed to the breaking of unsaturated covalent bonds and the continuous removal of oxygen atoms under high temperature. The Fe3O4 peak intensity decreases with increasing temperature, which is consistent with the results observed in XRD.

[0084] In this example, XRD analysis was performed on iron-based biochar at different temperatures. Under low temperature conditions, the pyrolysis product was mainly low-crystalline hematite (Fe2O3), which was further converted into crystalline magnetite (Fe3O4), wollastonite (FeO) and zero-valent iron (Fe) as the temperature increased. 0 ), the reaction process is shown in equations (1), (2) and (3). SiO2 with the same crystal plane appears under all temperature conditions. As a silicon-loving plant, the silicon in rice is mainly polymeric silicon and water-soluble silicic acid. Polymeric silicon and water-soluble silicic acid exist in the form of silicon phytosomes, with a content of up to 35%–38% of the dry weight, which plays a role in providing nutrition and protecting the plant body. During the pyrolysis process, silicon and carbon interact with each other, with carbon protecting silicon from dissolution and silicon protecting carbon from loss, thus forming a stable biochar material with a certain degree of anti-degradation ability. At higher pyrolysis temperatures, the silicon ash is transformed from an amorphous state to nano-SiO2 crystalline particles.

[0085] Example 5

[0086] This example tests the effect of different pH values on the performance of materials in removing Cr(VI), i.e., hexavalent chromium. The experiment found that pH can significantly affect the ability of iron-based biochar materials to remove hexavalent chromium, so the pH conditions are optimized first. Accurately weigh 15 mg (0.0150 g ± 0.0005 g) of iron-carbon materials prepared at different pyrolysis temperatures into 50 mL polypropylene centrifuge tubes, and add 10 mL of 30 mg / L hexavalent chromium solution (pH = 2, 3, 5) of different pH values, and then immediately place on a shaker. Samples are taken after 60 minutes, and two control groups are set for each treatment. Filter using a 0.22 μm fiber membrane, and use diphenylcarbazide spectrophotometry to determine the concentration of hexavalent chromium in the solution. The removal rate of hexavalent chromium of the material and the removal capacity of hexavalent chromium per unit mass of iron of the material are calculated.

[0087] Two control groups were set up for each treatment, along with an equal amount of zero-valent iron (ZVI) added, an iron-based biochar material (Fe-C) with exogenously added iron, and a control without the material. The iron-based biochar material with exogenously added iron was prepared according to the method described in Patent No. 202411748726. Briefly, corn stover was ground and fired in a muffle furnace at 340°C for 1 hour. The resulting biochar was soaked in a ferrous sulfate solution and then fired in a tube furnace at 700°C for 1 hour. The iron was in the form of ferrous carbide with an iron content of approximately 58%.

[0088] The Cr(VI) removal capacity of material unit mass iron and the Cr(VI) removal rate of material are calculated by formula (4) and formula (5), respectively:

[0089]

[0090] Where RC is the removal capacity of Cr(VI) per unit mass of iron (mg / g), RE is the removal rate of Cr(VI) (%), C0 is the initial concentration (mg / L), C e is the concentration after reaction (mg / L), V is the volume of the reaction solution, m is the mass of the iron-carbon material (g), m Fe is the mass of iron in the material.

[0091] Figure 5 The effect of BC on the removal of Cr(VI) in water under different pH conditions is shown in Figure 2. The ability of all materials to remove Cr(VI) increases with the decrease of the pH of the solution. The best effect is achieved when the pH is 2, which indicates that the acidic environment is conducive to the removal of Cr(VI) by iron-carbon materials. This may be related to the zero-point charge of biochar. When the reaction system is lower than the pH of biochar, the removal of Cr(VI) by iron-carbon materials increases. zpc When the pH value is low, it is conducive to the protonation of biochar, and the positively charged biochar is easy to combine with the negatively charged Cr(VI) anion. Under low pH conditions, excess H +Ions will corrode the oxide film of the iron-carbon material, exposing the reactive sites of the material, which will also be more conducive to the reaction. Under high pH conditions, the Cr(III) produced by reduction and the Fe(III) produced by oxidation are easy to react with OH in water. - The combination forms an insulating layer of oxyhydroxide, which blocks electron transfer to Cr(VI), inhibiting Cr(VI) removal. At pH 2, a comparison of the Cr(VI) removal rates of all materials shows the following: BC900 (99.31%) ≈ ZVI (100%) > Fe-C (97.27%) > BC700 (78.39%) > BC500 (42.45%) > BC300 (16.44%). BC900's performance is comparable to commercial zero-valent iron and superior to Fe-C, achieving virtually 100% removal of Cr(VI) from aqueous solutions.

[0092] Furthermore, if Figure 6 As shown, the Cr(VI) removal capacity per unit mass of iron for each material increases with decreasing pH, consistent with the removal rate trend, reaching a maximum removal amount at pH = 2. At pH = 2, the order of Cr(VI) removal capacity per unit mass of iron is BC900 (180.44 mg / g) > BC700 (175.33 mg / g) > BC500 (127.97 mg / g) > BC300 (67.61 mg / g) > Fe-C (33.57 mg / g) > ZVI (20 mg / g). The Cr(VI) removal capacity per unit mass of iron produced by the present invention is much higher than that of exogenously added iron-based biochar Fe-C and zero-valent iron. BC900 has the highest Cr(VI) removal capacity per unit mass of iron, 180.44 mg / g.

[0093] In summary, at pH = 2, iron-based biochar BC900 and BC700 materials have better Cr(VI) removal performance, with removal rates of 99.31% and 78.39%, respectively, and the removal capacity of Cr(VI) per unit mass of iron is 180.44 mg / g and 127.97 mg / g, respectively.

[0094] This example also screened the conditions for removing Cr(VI) using iron-based biochar materials BC700 and BC900. Under the optimal pH conditions, for example, pH = 2, the materials BC700 and BC900 with the better effects were selected for further optimization of the reaction conditions. A comprehensive test was conducted using three variable conditions: material (BC700 and BC900), material dosage (5, 10, and 15 mg), and initial concentration (30 mg / L, 50 mg / L, and 100 mg / L). A total of 18 sets of condition combinations were performed, and the remaining experimental conditions were the same as in Example 2. After the reaction, the Cr(VI) concentration was measured, and the Cr(VI) removal capacity per unit mass of iron in the material and the Cr(VI) removal rate of the material were calculated.

[0095] like Figure 7 As shown in the figure, under the same conditions, the overall removal effect is: BC900>BC700. With increasing dosage, the removal rate increases, as more material provides reactive sites to promote rapid reaction. With increasing initial concentration, the removal rate decreases, possibly because the material does not fully react with Cr(VI) within a limited time. When the initial concentration of BC900 in the reaction system is 30mg / L and 50mg / L and the dosage is 15mg, the maximum removal rates achievable within 1 hour are 98.72% and 98.27%, respectively. Figure 8 As shown in the figure, under similar removal rate conditions, the removal capacity of Cr(VI) per unit mass of iron in the material with an initial concentration of 50 mg / L is 297.37 mg / g, which is much higher than the 172.78 mg / g of the initial concentration of 30 mg / L.

[0096] In summary, the optimal reaction conditions were pH = 2, material BC900, and an initial concentration of 50 mg / L. The highest removal rate was 98.27%, and the maximum removal capacity of Cr(VI) per unit mass of iron was 297.37 mg / g.

[0097] This example also analyzes the adsorption and reduction effects of iron-based biochar BC900 on Cr(VI) removal. Chromium removal from solution primarily involves two mechanisms: adsorption and reduction. Cr(VI) can be reduced to Cr(III) and retained in solution, or it can be adsorbed on the surface of the material as either Cr(III) or Cr(VI). The adsorption contribution specifically refers to the proportion of Cr(VI) adsorbed by BC900 that was not reduced to the total Cr(VI) removed. This value can be quantitatively determined by desorption with 1.5M hydrochloric acid. The specific operating procedure is as follows: The adsorption equilibrium system (2 hours) is vacuum filtered (0.22μm filter membrane) to collect the adsorbed BC900. The BC900 is then washed three times with pure water to remove any Cr(VI) attached to the BC900 surface (the non-adsorbed portion). The washed BC900 is placed in a 50mL centrifuge tube, 10mL of 1.5M hydrochloric acid solution is added, and the mixture is shaken at 25°C and 160rpm for 24 hours to fully desorb. The concentrations of total chromium and Cr(VI) in the desorption solution were determined, and the concentration of Cr(III), i.e., trivalent chromium, was calculated by the difference method.

[0098] This example analyzes the dominant species in the reduction reaction. Compared with the reducing groups, the main reducing species in the iron-based biochar material is iron. The iron that reduces Cr(VI) mainly includes Fe 0 , surface-bound Fe(II), and dissolved Fe(II). Their relative contributions were estimated by combining Fe(II) shielding experiments and experiments on changes in iron ion content in the presence or absence of Cr(VI). Based on the fact that 1,10-phenanthroline can form a complex with Fe(II) to inhibit the reaction between Fe(II) and Cr(VI), 2.88 mmol / L of Fe(II) is required to reduce 50 mg / L (0.96 mmol / L) of Cr(VI). The molar ratio of 1,10-phenanthroline to Fe(II) is approximately 3:1. The amount of 1,10-phenanthroline added was estimated to be 10.39 mmol / L, assuming a 20% excess, to ensure complete reduction of Cr(VI) by Fe(II). 0, 5, 10, and 15 mM 1,10-phenanthroline were added to batch experiments, and the removal rates were measured. The difference between the minimum and maximum removal rates was the contribution of Fe(II). The batches with single addition of materials, co-addition of Cr(VI) and materials, and no addition of Cr(VI) were set up, and the pH was uniformly adjusted to 2. The concentrations of total dissolved Fe and Fe(II) in the reaction were detected, and the concentration of Fe(III) was calculated. Based on the difference in the concentrations of dissolved Fe(II) in the two, the contribution rate of dissolved Fe(II) was estimated based on the theoretical amount of Cr(VI) that could be reduced. Finally, the contribution of surface-bound Fe(II) = the contribution rate of Fe(II) - the contribution rate of dissolved Fe(II), Fe 0 Contribution rate of Fe(II) = total removal rate - adsorption contribution rate - contribution rate of Fe(II).

[0099] The desorption experiment measured the concentration of Cr(VI) to be 0.16 mg / L, which means that the Cr(VI) removed by adsorption only accounted for 0.32% of the total Cr(VI) removal rate, indicating that BC900 mainly removes Cr(VI) by reduction. During the BC900 removal of Cr(VI), the concentrations of Cr(VI), Cr(III) and total chromium in the solution in the reaction system changed as shown below: Figure 9 As shown in a, the concentrations of Cr(VI) and total chromium decreased rapidly within the first 10 minutes, while the concentration of Cr(III) increased slightly, indicating that chromium was quickly removed after BC900 was added to the system. After 1,10-phenanthroline was added to the system, the Cr(VI) removal rate of the system decreased significantly, and the inhibition levels of 5, 10, and 15 mM 1,10-phenanthroline were similar, indicating that 1,10-phenanthroline was excessive. In the treatment with 15 mM 1,10-phenanthroline, the removal rate of Cr(VI) decreased from 99.05% to 31.80%, and the contribution of total Fe(II) was calculated to be 68.85%, which also illustrates the role of the presence of other forms of iron. In the reaction system without Cr(VI), the change in the concentration of dissolved iron is shown in the figure below: Figure 9 As shown in c, Fe(II) increases with time and finally stabilizes, with a maximum concentration of 62 μM; in the system with Cr(VI) ( Figure 9 d), Fe(II) has been maintained at a low level and is basically not detected. Based on this calculation, theoretically, Fe(II) can reduce 1.07 mg / L of Cr(VI), accounting for 2.18% of the total removal rate. Further calculation shows that the contribution of bound Fe(II) is 66.67%, while Fe 0 The contribution was 31.15%.

[0100] Cr(VI) removal contribution Figure 10 As shown in the figure, the final estimation shows that in the process of Cr(VI) removal, the contribution of adsorption is 0.32%, the contribution of reduction is 99.68%, of which the contribution of bound Fe(II) is 66.67%, and the contribution of Fe(II) is 1. 0 The contribution of Fe(II) was 30.83%, and the contribution of Fe(II) was 2.18%. BC900 mainly removed Cr(VI) by reduction, in which bound Fe(II) was the dominant species, followed by Fe 0 .

[0101] This example also tested the ability of iron-based biochar BC900 to remove Cr(VI) from water. 100 mg (0.1000 g ± 0.0005 g) of iron-carbon material was accurately weighed into a 250 mL glass bottle, 100 mL of Cr(VI) solution (50 mg / L, pH = 2) was added, and then immediately placed on a shaker. Samples were taken at 1, 4, 7, 10, 15, 20, 30, 40, 60, and 120 min, 1 mL each time, and filtered using a 0.22 μm filter membrane. The concentration of Cr(VI) was determined and the adsorption amount of the material was calculated.

[0102] like Figure 11 As shown in the data, BC900 can achieve a Cr(VI) adsorption capacity of 29.3 mg / g within 1 minute, and the C(VI) removal rate is 82.56%. When the reaction time is 1 hour, the Cr(VI) adsorption capacity can reach 32.97 mg / g, and the C(VI) removal rate is as high as 98.60%, indicating that the material can achieve rapid removal of Cr(VI) within 1 hour.

[0103] This embodiment also provides a method for preparing an iron-based biochar material using iron-rich biomass for use in removing hexavalent chromium from water and contaminated soil. In this embodiment, the iron-based biochar BC900 is applied to soil remediation. The soil is collected and air-dried, and sieved with a 10-mesh sieve. A certain amount of potassium dichromate solution (pH = 2) is added to the soil and stirred evenly to make the theoretical value of Cr(VI) 100 mg / kg. The soil is placed at room temperature for 20 days to simulate the aging process of soil containing natural Cr(VI). The prepared soil is air-dried and then sieved with a 10-mesh sieve for later use. The concentrations of Cr(VI) and total Cr, as well as the physical and chemical properties of Cr(VI) and total Cr, are finally determined, as shown in Table 2.

[0104] Table 2 Physical and chemical properties of simulated contaminated soil

[0105]

[0106] Take 100g of contaminated soil and place it in a 250mL beaker. Add 2% (2g) BC900 biochar and 10mL of water (water-soil ratio 1:10) and mix well to make the soil moist but not caking and sandy in texture. Seal it with plastic wrap and place it in an incubator at 25°C. Keep the water-soil ratio repaired for 45 days. During this period, add water and stir to maintain a fixed moisture content. Set up a treatment without adding materials as a comparison, and set up 3 parallels for each treatment. Samples were taken on the 1st, 5th, 10th, 20th and 45th day of repair to determine the total Cr(VI) content, available Cr and leaching toxicity of the soil.

[0107] In the chromium toxicity leaching, acetic acid was used as the leaching agent to evaluate the effect of industrial landfill filtrate on the remediation effect. The changes in the toxicity leaching of Cr and Cr(VI) in the soil during the remediation process are shown in Figure 2. Figure 13 and Figure 14 As shown, the leached concentrations of Cr and Cr(VI) dropped sharply within one day, then stabilized over time. After 45 days of remediation, the final leached concentration of Cr(VI) was 0.01 mg / L, significantly lower than the 5.44 mg / L in the CK treatment. The leached concentration of total Cr was 1.75 mg / L, lower than the 7.48 mg / L in the CK treatment. Both Cr(VI) concentrations met the Class II water quality standard (0.01 mg / L) of China's Groundwater Quality Standard (GB / T14848-2017).

[0108] In this example, the chromium in the soil after DTPA extraction and remediation is the active part that can be absorbed by plants or can migrate in the environment, which is used to evaluate the bioavailability of chromium in the soil. Figure 12 As shown in the figure, 45 days after the addition of the remediation materials, the available Cr content decreased significantly, with the soil available Cr concentration decreasing from an initial 173.16 mg / kg to 30.16 mg / kg. According to the "Soil Environmental Quality Agricultural Land Soil Pollution Risk Control Standard" (GB15618-2018), different soil use types and pH levels require different soil chromium limits. Comparing the pH of the remediated soil with its limit, it was found that the remediated soil remained below the agricultural land risk screening value of 200 mg / kg, indicating that the remediated soil poses a low risk to agricultural product quality and safety, crop growth, or the soil ecological environment.

[0109] It should be noted that, in this document, the terms "comprises," "includes," or any other variations thereof are intended to encompass non-exclusive inclusion, such that a process, apparatus, article, or method comprising a series of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, apparatus, article, or method. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of other identical elements in the process, apparatus, article, or method comprising the element.

[0110] The above description is only a preferred embodiment of the present application and does not limit the patent scope of the present application. Any equivalent structure or equivalent process transformation made using the contents of the present application specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present application.

Claims

1. A method for preparing iron-based biochar material using iron-rich biomass, characterized in that: include: (1) cleaning the iron-rich rice roots and drying the iron-rich rice roots; (2) chopping, grinding, and sieving the dried iron-rich rice roots in sequence to obtain rice root powder; (3) mixing the rice root powder and pure water, adding a magnetic stirrer to stir, and obtaining a mixture; (4) drying and grinding the mixture in sequence to obtain a powder to be processed; (5) The powder to be treated is placed in a tubular furnace and nitrogen is introduced, and the pyrolysis temperature is gradually increased from room temperature to 900°C to pyrolyze the powder to be treated to obtain iron-based biochar materials at different pyrolysis temperatures; wherein the iron-based biochar materials are used to remove hexavalent chromium in water and soil.

2. The method for preparing iron-based biochar material using iron-rich biomass according to claim 1, characterized in that: In step (3), the mixing ratio of rice root powder and pure water is 3 g:100 mL, the stirring temperature is 50° C., the stirring speed is 800-1200 rpm, and the stirring time is 2 h.

3. The method for preparing iron-based biochar material using iron-rich biomass according to claim 1, characterized in that: The pyrolysis temperature in step (5) was gradually increased from room temperature to 300°C, 500°C, 700°C and 900°C at 10°C / min.

4. The method for preparing iron-based biochar material using iron-rich biomass according to claim 1, characterized in that: The gas flow rate in step (5) is 50 mL / min and the pyrolysis time is 2 h.

5. The method for preparing iron-based biochar material using iron-rich biomass according to claim 1, characterized in that: The iron-rich rice roots are roots of indica rice or japonica rice. Varieties of indica rice include Huayou 86, and varieties of japonica rice include Nanjing 9108.

6. The method for preparing iron-based biochar material using iron-rich biomass according to claim 1, characterized in that: The iron content of the root of the iron-rich rice is greater than or equal to 1%.

7. The method for preparing iron-based biochar material using iron-rich biomass according to claim 1, characterized in that: The method further comprises the step (6): nitrogen doping the iron-based biochar material to improve the performance of the iron-based biochar material in a high pH system.

8. The method for preparing iron-based biochar material using iron-rich biomass according to claim 7, characterized in that: Nitrogen doping selects N chemical reagents or biopolymers with different nitrogen contents as nitrogen precursors, where 1≤N≤6; the chemical reagents include urea, ammonium nitrate and melamine, and the biopolymers include peptone, yeast powder and nitrogen-rich algae biomass.

9. The method for preparing iron-based biochar material using iron-rich biomass according to claim 8, characterized in that: In step (6), 10 g of rice root powder was mixed with 500 mL of methanol and ultrasonically treated at 70% intensity for 30 min. 20 g, 10 g, 5 g and 3.33 g of nitrogen precursor were added to the suspension so that the addition ratio of nitrogen precursor to rice root powder was 2:1, 1:1, 1:2 and 1:3, respectively. The suspension was heated at 80° C. for 8 hours to evaporate the methanol solvent.

10. Use of the method for preparing iron-based biochar material using iron-rich biomass as claimed in any one of claims 1 to 9 in removing hexavalent chromium from water and contaminated soil.

Images