An oxygen-activated iron-rich biochar, its preparation method and application

Abstract

This invention discloses an oxygen-activated iron-rich biochar, its preparation method, and its application, relating to the field of materials technology. The preparation method includes the following steps: pulverized biomass raw materials are subjected to high-temperature pyrolysis under oxygen-deficient conditions, cooled, and sieved to obtain raw biochar powder. This powder is then thoroughly mixed with ferric nitrate nonahydrate, and KOH solution is added dropwise under oxygen-purifying conditions until the solution pH is neutral. After solid-liquid separation, a precipitate is obtained, which is then freeze-dried and finally sieved to obtain the oxygen-activated iron-rich biochar. This invention utilizes high-purity oxygen to optimize the iron-rich biochar, resulting in a material with a large specific surface area, small average pore size, and a high number of micropores, significantly enhancing its adsorption capacity. Furthermore, it eliminates the risk of secondary pollution, has a simple preparation process, and is suitable for large-scale industrialization. In addition, it exhibits excellent solidification and stabilization properties for heavy metals, especially for the adsorption of variable-valence metals like arsenic, far exceeding that of commercially available modified biochar.

Description

Technical Field

[0001] This invention relates to the field of materials technology, and in particular to an oxygen-activated iron-rich biochar, its preparation method, and its application. Background Technology

[0002] In recent years, with the acceleration of industrialization, the emissions of greenhouse gases such as carbon dioxide, nitrous oxide, and methane have continued to increase, leading to frequent extreme weather events. Biochar, as a functional material with multiple environmental benefits, is widely used. It can capture greenhouse gases in the atmosphere through biochar sequestration technology, convert them into stable forms, and then store them in the soil for a long time, thereby increasing soil carbon sequestration and reducing greenhouse gas emissions.

[0003] To further improve the application performance of biochar, it is often modified. Currently, there are numerous biochar modification technologies, typically employing physical, chemical, and biochemical treatments to improve the properties and adsorption performance of biochar, optimize its surface structure, or add highly adsorbent materials. Among these, chemical modification is the most widely used and mature method, including modification using acid-base neutralization, redox reactions, and polymer materials. For example, iron and calcium ion solutions react with biochar in redox reactions to alter its properties, improving its specific surface area and increasing porosity, thereby enhancing its adsorption performance. Further modification through doping based on the reaction of metal ion solutions with biochar can further improve the material's adsorption performance. However, most doping modification methods are expensive, complex, and offer only minor performance improvements, making them unsuitable for large-scale production. Therefore, there is an urgent need for a simple, readily available, low-cost material optimization method that can be mass-produced and significantly improve adsorption efficiency. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of existing technologies by providing an oxygen-activated iron-rich biochar, its preparation method, and its application.

[0005] The objective of this invention is achieved through the following technical solution: In a first aspect, the present invention provides a method for preparing oxygen-activated iron-rich biochar, comprising the following steps: S1: After crushing the biomass raw material, it is first sieved to obtain sieved biomass raw material. Under anaerobic conditions, the sieved biomass raw material is subjected to high-temperature pyrolysis, cooled, and then sieved a second time to obtain raw biochar powder. S2: The raw biochar powder and ferric nitrate are mixed and stirred in deionized water to obtain a first solution. Then, KOH solution is added under the condition of oxygen introduction to obtain a second solution. The second solution is washed with deionized water until the pH value of the second solution is 6.9~7.1. Then, the second solution is centrifuged or allowed to stand to precipitate for solid-liquid separation to obtain a precipitated solid. The precipitated solid is freeze-dried and finally subjected to a third sieve to obtain oxygen-activated iron-rich biochar.

[0006] Furthermore, the biomass raw materials are selected from corn stalks, wheat stalks, bamboo, wood, rice stalks, and rice husks.

[0007] Furthermore, the mass ratio of raw biochar powder to ferric nitrate is 1:1 to 1:10; the mass ratio of raw biochar powder to deionized water is 1:50.

[0008] Furthermore, the mesh size of the sieve used in the first sieving in step S1 is 100~200 mesh.

[0009] Furthermore, the oxygen-deficient condition in step S1 specifically refers to an environment where air is isolated and no gas is introduced.

[0010] Furthermore, in step S1, the high-temperature pyrolysis temperature is 300℃~700℃; the high-temperature pyrolysis time is 2~3 h; and the high-temperature pyrolysis heating rate is 5~10℃ / min.

[0011] Furthermore, in step S1, the cooling temperature is 20℃~25℃; the cooling time is 2h~24h; and the mesh size of the sieve used for the second sieve is 100~200 mesh.

[0012] Further, in step S2, the mixing and stirring time is 1~10h; the partial pressure of the oxygen gas is 0.05~0.2 MPa; the flow rate of the oxygen is 8~15 L / min; and the purity of the oxygen is greater than 99wt%.

[0013] Furthermore, the concentration of the KOH solution in step S2 is 2~3 mol / L.

[0014] Furthermore, the freeze-drying process described in step S2 involves pre-freezing. The pre-freezing temperature is -18℃ to -24℃, and the pre-freezing time is 2 to 30 hours. During freeze-drying, the sample temperature is 20℃ to -40℃, the cold trap temperature is -40℃ to -80℃, the vacuum pressure is 1 to 60 Pa, and the freeze-drying time is 2 to 7 days.

[0015] Secondly, the present invention also provides an oxygen-activated iron-rich biochar obtained by the above preparation method.

[0016] Thirdly, the present invention also provides the application of oxygen-activated iron-rich biochar in the remediation of arsenic-contaminated soil and / or water.

[0017] Compared with the prior art, the beneficial effects of the present invention are: (1) By using high-purity oxygen to optimize iron-rich biochar, the material itself has a large specific surface area, small average pore size and a large number of micropores, which further improves the contact area between the material and heavy metal ions in the solution system. (2) The number of effective functional groups of the material increases, which greatly enhances the adsorption capacity. Furthermore, the biochar raw material comes from nature and is returned to nature, so there is no risk of secondary pollution. It can be applied to the solidification and stabilization of heavy metals in soil and water. (3) The preparation process is simple, which reduces energy consumption, time and cost, and is suitable for large-scale industrialization; (4) It has excellent solidification and stabilization properties for heavy metals, especially for the adsorption of arsenic, a variable-valence metal, which far exceeds that of modified biochar on the market. Attached Figure Description

[0018] Figure 1 A schematic diagram illustrating the preparation of oxygen-activated iron-rich biochar provided by this invention; Figure 2 This is a scanning electron microscope image of the oxygen-activated iron-rich biochar obtained in Example 1 of the present invention at 500x magnification. Figure 3 This is a scanning electron microscope image of the oxygen-activated iron-rich biochar obtained in Example 1 of the present invention at 3320x magnification. Figure 4 The image shows the pore size distribution curves of the rice husk biochar powder prepared in Example 1 of this invention, the oxygen-activated iron-rich biochar, and the iron-rich biochar obtained in Comparative Example 1. Figure 5 This is a fitting graph of the adsorption isotherm data of oxygen-activated iron-rich biochar obtained in Example 1 of the present invention; Figure 6 This is a scatter plot of the adsorption amount and adsorption efficiency of rice husk biochar powder obtained in S1 of Example 1 of the present invention under pyrolysis temperature conditions of 300℃, 500℃ and 700℃. Figure 7 The bar graph shows the adsorption results of arsenic by equal amounts of iron ions contained in the rice husk biochar powder prepared in Example 1 of the present invention, oxygen-activated iron-rich biochar, ferrous ore obtained in Comparative Example 5, and oxygen-activated iron-rich biochar. Figure 8 The bar graph shows the adsorption results of arsenic on the rice husk biochar powder prepared in Example 1 of this invention, oxygen-activated iron-rich biochar, oxygen-activated biochar obtained in Comparative Example 4, iron-rich biochar obtained in Comparative Example 3, and oxygen-activated iron-rich biochar obtained in Examples 2 and 3. Figure 9 The bar graph shows the adsorption results of arsenic on rice husk biochar powder prepared in Example 1 of the present invention, oxygen-activated iron-rich biochar, oxygen-activated iron-rich biochar prepared in Examples 4-6, and ferrous ore prepared in Comparative Example 5. Figure 10 This is a graph showing the adsorption efficiency of each basic material of the oxygen-activated iron-rich biochar obtained in Example 1 of the present invention and its contribution rate to the adsorption performance of the oxygen-activated iron-rich biochar. Detailed Implementation

[0019] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0020] In a first aspect, the present invention provides a method for preparing oxygen-activated iron-rich biochar, comprising the following steps: S1) After crushing the biomass raw material, it is first sieved to obtain sieved biomass raw material. Under anaerobic conditions, the sieved biomass raw material is subjected to high-temperature pyrolysis, cooled, and then sieved again to obtain raw biochar powder. S2) The raw biochar powder and ferric nitrate are mixed and stirred in deionized water to obtain a first solution. Then, KOH solution is added under the condition of oxygen introduction to obtain a second solution until the pH value of the second solution is 6.9~7.1. Subsequently, the second solution is centrifuged or allowed to stand to precipitate for solid-liquid separation to obtain a precipitated solid. The precipitated solid is freeze-dried and finally subjected to a third sieve to obtain oxygen-activated iron-rich biochar.

[0021] Furthermore, the mass ratio of raw biochar powder to ferric nitrate is 1:1 to 1:10; the mass ratio of raw biochar powder to deionized water is 1:50.

[0022] Figure 1 This is a schematic diagram illustrating the preparation of oxygen-activated iron-rich biochar provided by the present invention.

[0023] In this invention, there are no special restrictions on the source of any raw materials; they can be commercially available.

[0024] In one specific embodiment of the present invention, the biomass raw material is a biomass raw material well known to those skilled in the art, and there are no special limitations, including but not limited to one or more of corn stalks, wheat stalks, bamboo, wood, rice stalks and rice husks. All of the above biomass raw materials can be used to prepare oxygen-activated iron-rich biochar by the preparation method of the present invention.

[0025] In one specific embodiment of the present invention, the biomass raw material is obtained by removing surface adhering substances, air drying, pulverizing and then passing through a first sieve to obtain sieved biomass raw material; the mesh size of the sieve used for the first sieve is preferably 100 to 200 mesh.

[0026] The screened biomass raw material is subjected to high-temperature pyrolysis under anaerobic conditions. In this invention, the anaerobic conditions specifically refer to an environment where air is isolated and no gas is introduced. The preferred heating rate for high-temperature pyrolysis is 5~10℃ / min. Optionally, the heating rate is 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min, 10℃ / min, or any two of the above values. The preferred temperature for high-temperature pyrolysis is 300℃~700℃. Optionally, the temperature is 300℃, 400℃, 500℃, 600℃, 700℃, or any two of the above values. The preferred holding time for high-temperature pyrolysis is 2~3 h. Optionally, the holding time is 2 h, 2.2 h, 2.5 h, 2.8 h, 3 h, or any two of the above values.

[0027] After high-temperature pyrolysis, the material is cooled and then sieved a second time to obtain raw biochar. The cooling time is 2h to 24h. The preferred cooling temperature is 20℃ to 25℃. The preferred mesh size of the sieve used for the second sieve is 100 to 200 mesh.

[0028] The raw material biochar and iron salt are mixed and stirred in water to obtain a mixed solution; the iron salt is a water-soluble iron salt well known to those skilled in the art, and there are no special restrictions, but ferric nitrate is preferred in this invention; the mass ratio of raw material biochar to iron salt is preferably 1:(1~10); optionally, the mass ratio of raw material biochar to iron salt is 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10 or any two of the above ratios; the mass ratio of raw material biochar to water is preferably 1:(50~200); optionally, the mass ratio of raw material biochar to water is 1:50, 1:80, 1:100, 1:120, 1:50, 1:180, 1:200 or any two of the above ratios; the mixing and stirring time is preferably 1~10 h; optionally, the mixing and stirring time is 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h or any two of the above values.

[0029] Then, KOH solution is added under oxygen-introduced conditions; the purity of the oxygen is preferably greater than or equal to 99%, more preferably greater than or equal to 99.5%, even more preferably greater than or equal to 99.9%, and most preferably 99.99%; the partial pressure of the introduced oxygen is preferably 0.05~0.2 MPa; optionally, the partial pressure of the introduced oxygen is 0.05 MPa, 0.08 MPa, 0.1 MPa, 0.12 MPa, 0.15 MPa, 0.18 MPa, 0.2 MPa, or any two of the above values; the flow rate of the introduced oxygen is preferably 8~15 L / min; optionally, the flow rate of the introduced oxygen is 8 L / min, 9 L / min, 10 L / min, 11 L / min, 12 L / min, 13 L / min, 14 L / min, 15 ... L / min or any two of the above values; specifically, in this invention, oxygen is introduced through an aeration head, and after passing through the aeration head, it can form a continuous and dense stream of small bubbles in the mixed solution; potassium hydroxide activation can promote the formation of more oxidizing functional groups, significantly increasing the specific surface area, pore volume and oxygen-containing functional groups of biochar. The concentration of the KOH solution is preferably 2~3 mol / L; optionally, the concentration of the KOH solution is 2 mol / L, 2.1 mol / L, 2.2 mol / L, 2.3 mol / L, 2.4 mol / L, 2.5 mol / L, 2.6 mol / L, 2.6 mol / L, 2.7 mol / L, 2.8 mol / L, 2.9 mol / L, 3 mol / L or any two of the above values.

[0030] In one specific embodiment of the present invention, it is preferable to first introduce oxygen and then add KOH solution; specifically, after introducing oxygen for 15 to 30 minutes, KOH solution is added.

[0031] In one specific embodiment of the present invention, the KOH solution is preferably added in small amounts multiple times until the pH value of the solution is 6.9~7.1.

[0032] In one specific embodiment of the present invention, KOH solution is added until the pH value of the solution is 6.9, 6.95, 6.98, 7, 7.02, 7.05, 7.08, 7.1 or any two of the above values.

[0033] In one specific embodiment of the present invention, KOH solution is added until the pH value of the solution is 6.9-7.1. After washing with deionized water several times, the solution is centrifuged, allowed to settle and precipitate or filtered to separate the solid and liquid. Then the supernatant is discarded and the solid is freeze-dried to obtain oxygen-activated iron-rich biochar.

[0034] In one specific embodiment of the present invention, after removing the supernatant, the solid is preferably washed with deionized water, and then the solid is freeze-dried to obtain oxygen-activated iron-rich biochar.

[0035] In a specific embodiment of the present invention, pre-freezing is preferably performed before freeze-drying; the pre-freezing temperature is preferably -18℃ to -24℃; optionally, the pre-freezing temperature is -18℃, -19℃, -20℃, -21℃, -22℃, -23℃, -24℃ or any two of the above values; the pre-freezing time is preferably 2 to 30 h; optionally, the pre-freezing time is 2 h, 4 h, 6 h, 8 h, 10 h, 12 h, 14 h, 16 h, 18 h, 20 h, 22 h, 24 h, 26 h, 28 h, 30 h or any two of the above values.

[0036] The sample temperature during freeze-drying is preferably 20℃ to -40℃; optionally, the sample temperature is 20℃, 15℃, 14.9℃, 10℃, 5℃, 0℃, -5℃, -10℃, -15℃, -20℃, -25℃, -26.8℃, -30℃, -35℃, -40℃, or any two of the above values. The cold trap temperature during freeze-drying is preferably -40℃ to -80℃; optionally, the cold trap temperature is -40℃, -42℃, -44℃, -44.3℃, -48℃, -50℃, -55℃, -60℃, -65℃, -70℃, -75℃, -80℃, or any two of the above values. The vacuum pressure during freeze-drying is preferably 1~60 Pa; optionally, the vacuum pressure during freeze-drying is 1 Pa, 5 Pa, 10 Pa, 15 Pa, 20 Pa, 25 Pa, 30 Pa, 35 Pa, 40 Pa. Pa, 45 Pa, 46 Pa, 50 Pa, 55 Pa, 60 Pa or any two of the above values; the freeze-drying time is preferably 2 to 7 days; optionally, the freeze-drying time is 2, 3, 4, 5, 6, 7 days or any two of the above values.

[0037] In one specific embodiment of the present invention, after freeze-drying, the biochar is preferably sieved to obtain oxygen-activated iron-rich biochar; the mesh size of the sieve used for sieving is preferably 100-200 mesh.

[0038] This invention optimizes the generation of iron-rich biochar using high-purity oxygen, enhancing the material's pore structure, specific surface area, and functional groups to significantly improve its adsorption capacity. Furthermore, since the raw materials are derived from and return to nature, it is widely applicable to soil and water bodies, posing no risk of secondary pollution. It can be used for the solidification and stabilization of heavy metals in soil and water. The preparation process is simple, significantly reducing energy consumption, time, and cost compared to high-temperature methods like 700℃, making it suitable for large-scale industrialization. Its solidification and stabilization performance for heavy metals is excellent, especially its adsorption of variable-valence metals like arsenic, which far surpasses that of commercially available modified biochar.

[0039] Secondly, the present invention also provides an oxygen-activated iron-rich biochar prepared by the above preparation method.

[0040] Thirdly, the present invention also provides an application of the oxygen-activated iron-rich biochar prepared by the above preparation method in the remediation of heavy metal contaminated soil and / or water bodies.

[0041] In one specific embodiment of the present invention, the heavy metal is preferably a variable valence heavy metal, and more preferably a metalloid arsenic.

[0042] To further illustrate the present invention, the following detailed description of an oxygen-activated iron-rich biochar, its preparation method, and its application is provided in conjunction with embodiments.

[0043] All reagents used in the following examples are commercially available.

[0044] Example 1: S1: Rice husks are fed into the inlet and crushed to 100 mesh using a crusher. The crushed rice husks are then fed into the carbonization furnace through the crusher outlet. The heating rate of the carbonization furnace is set to 5℃ / min, and the carbonization is carried out at 500℃ under conditions of complete air isolation for 2 hours. After that, the carbonization is cooled at 25℃ for 2 hours. After cooling, the carbon is discharged intermittently through the discharge pipe to obtain raw biochar. The raw biochar is then sieved through a 100-mesh sieve to obtain sieved rice husk biochar powder (RHB). S2: Add 2 g of rice husk biochar powder and 10 g of ferric nitrate nonahydrate powder to 100 mL of deionized water and stir for 4 hours to obtain a mixed solution. Then, 99.99% pure oxygen is bubbled into the mixed solution to generate a continuous, fine stream of small bubbles. The partial pressure of the oxygen gas is 0.1 MPa, and the flow rate is 12 L / min. After 20 minutes, 2.5 mol / L KOH solution is added dropwise in small amounts several times, while monitoring the pH of the solution. The addition of KOH solution is stopped when the pH of the solution reaches 7 ± 0.05. The solution is then washed repeatedly with deionized water until it is neutral. After centrifugation, the solid and liquid are separated, and the supernatant is poured off to obtain a precipitate. The precipitate is pre-frozen at -18℃ for 24 hours. h, and then put it into a freeze dryer for 3 days. The freeze drying conditions are -26.8℃ for the sample, -44.3℃ for the cold trap, and 46Pa for the vacuum, until it is completely dried into powder. The powder is then passed through a 100-mesh sieve to obtain oxygen-activated iron-rich biochar (OFRHB), which is then stored under shade-drying conditions.

[0045] Example 2: S1: Rice straw is fed into the inlet and crushed to 200 mesh using a crusher. The crushed rice husk material enters the carbonization furnace through the crusher outlet. The heating rate of the carbonization furnace is set to 5℃ / min, and high-temperature pyrolysis is carried out at 500℃ under the condition of isolating air and not introducing any gas for 2 hours. Then, it is cooled at 20℃ for 24 hours. After cooling, the material is discharged intermittently through the discharge pipe to obtain raw biochar. The raw biochar is then screened through a 100-mesh sieve to obtain sieved rice straw biochar powder. S2: Add 2 g of rice straw biochar powder and 10 g of ferric nitrate nonahydrate powder to 100 mL of deionized water and stir for 4 hours to obtain a mixed solution. Then, 99.99% pure oxygen is bubbled into the mixed solution to generate a continuous, fine stream of small bubbles. The partial pressure of the oxygen gas is 0.1 MPa, and the flow rate is 10 L / min. After 30 minutes, 2.5 mol / L KOH solution is added dropwise in small amounts several times, while monitoring the pH of the solution. The addition of KOH solution is stopped when the pH of the solution reaches 7 ± 0.05. The solution is then washed repeatedly with deionized water until it is neutral. After centrifugation, the solid and liquid are separated, and the supernatant is poured off to obtain a precipitate. The precipitate is pre-frozen at -22℃ for 6 hours. h, and then put it into a freeze dryer for 5 days. The freeze drying conditions are 14.9℃ for the sample, -48℃ for the cold trap, and 1Pa for the vacuum, until it is completely dried into powder. The powder is then passed through a 100-mesh sieve to obtain oxygen-activated iron-rich biochar (OFRSB), which is then stored under shade-drying conditions.

[0046] Example 3: The preparation conditions were the same as in Example 1, except that rice husks were replaced with wheat straw to obtain oxygen-activated iron-rich biochar (OFWSB).

[0047] Example 4: The preparation conditions were the same as in Example 1, except that 2 g of ferric nitrate nonahydrate powder particles were weighed to obtain oxygen-activated iron-rich biochar (OFRHB).

[0048] Example 5: The preparation conditions were the same as in Example 1, except that 4 g of ferric nitrate nonahydrate powder particles were weighed to obtain oxygen-activated iron-rich biochar (OFRHB).

[0049] Example 6: The preparation conditions were the same as in Example 1, except that 20 g of ferric nitrate nonahydrate powder particles were weighed to obtain oxygen-activated iron-rich biochar (OFRHB).

[0050] Comparative Example 1: Preparation of biochar at 300℃: The preparation conditions were the same as those in step S1 of Example 1, except that the rice husk biochar powder was obtained by high-temperature pyrolysis at 300°C under conditions of isolation from air and no gas being introduced.

[0051] Comparative Example 2: Preparation of biochar at 500℃: The preparation conditions were the same as those in step S1 of Example 1, except that the rice husk biochar powder was obtained by high-temperature pyrolysis at 700°C under conditions of isolation from air and no gas being introduced.

[0052] Comparative Example 3: Preparation of iron-rich biochar: The preparation conditions were the same as in Example 1, except that 99.99% pure oxygen was not introduced into the mixed solution to obtain iron-rich biochar (FRHB).

[0053] Comparative Example 4: Preparation of oxygen-carrying biochar: The preparation conditions were the same as in step S1 of Example 1, and rice husk biochar powder (RHB) was obtained. The biochar was placed in a pressure-resistant sealed container, and then degassed in a vacuum environment of -0.1 MPa for 2 hours. Then, 99.99% oxygen was pumped in at a pressure of 0.15 MPa for 4 hours to obtain oxygen-carrying biochar (ORHB).

[0054] Comparative Example 5: Preparation of ferrohydrate: The preparation conditions were the same as in step S2 of Example 1, except that rice husk biochar powder was not added and oxygen was not introduced. Only ferric nitrate nonahydrate powder particles were weighed to obtain ferrohydrate (Fh).

[0055] The oxygen-activated iron-rich biochar (OFRHB) obtained in Example 1 was analyzed using scanning electron microscopy, and its scanning electron micrograph is shown below. Figure 2 and Figure 3 As shown. By Figure 2 and Figure 3 It can be seen that the oxygen-activated iron-rich biochar (OFRHB) prepared in Example 1 has macropores embedded in mesopores, and micropores embedded in mesopores, which greatly increases the specific surface area of ​​the material.

[0056] The pore size distribution of the rice husk biochar powder (RHB) prepared in Example 1, the iron-rich biochar (FRHB) prepared in Comparative Example 1, and the oxygen-activated iron-rich biochar (OFRHB) prepared in Example 1 was detected using physical adsorption. The pore size distribution curves are shown in the figure below. Figure 4 As shown in Table 1, the specific surface area and porosity parameters are as follows: Table 1. BET specific surface area and porosity parameters of biochar samples In the table, Indicates the specific surface area of ​​a material. Indicates the total pore volume. This indicates the volume of the micropores.

[0057] Depend on Figure 4 As can be seen, iron-rich biochar (FRHB) mainly adds mesopores and a small amount of micropores to the raw biochar, while oxygen-activated iron-rich biochar (OFRHB) adds a large number of micropores to the iron-rich biochar. Therefore, as shown in Table 1, oxygen-activated iron-rich biochar (OFRHB) has the largest specific surface area and the smallest average pore size.

[0058] The adsorption isotherm of oxygen-activated iron-rich biochar (OFRHB) obtained in Example 1 was measured, and the results were fitted. The specific method for measuring the adsorption isotherm of arsenic by oxygen-activated iron-rich biochar and fitting the data is as follows: Sodium arsenite (NaAsO2) solutions containing trivalent arsenic ions were prepared at concentrations of 1, 5, 10, 20, 50, 100, and 200 mg / L for later use. 2 mg of oxygen-activated iron-rich biochar was weighed into different 50 mL centrifuge tubes, with three parallel samples for each concentration. 20 mL of the prepared arsenic ion solution was slowly poured into each centrifuge tube for material adsorption experiments. The material addition amount was 0.1 g / L. The concentration after adsorption equilibrium was measured after 24 hours to obtain the adsorption results of different materials for arsenic. The residual concentration (C) of each group e ) and the corresponding equilibrium adsorption amount (Q) e Fitting was performed using the Langmuir model and the Freundlich model: Langmuir model: Freundlich model: Q e (mg / g) represents the amount of arsenic adsorbed by the material in its adsorption equilibrium state; C e q represents the equilibrium concentration (mg / L) of the solute in the aqueous solution. max Maximum adsorption capacity (mg / g) refers to the estimated amount of pollutant adsorbed; K L and K F It is a constant related to adsorption; The fitting graph of adsorption isotherm data is shown below. Figure 5 As shown, the maximum adsorption capacity (q) of oxygen-activated iron-rich biochar for arsenic was obtained. max The concentration reached 538.4572 mg / g, far exceeding the values ​​mentioned in commercial products and studies.

[0059] The adsorption performance of the material prepared above for arsenic was tested. The specific method for testing the adsorption performance of arsenic is as follows: A sodium arsenite (NaAsO2) solution with a concentration of 1 mg / L containing trivalent arsenic ions was prepared for use. 2 mg of the above material was weighed into different 50 mL centrifuge tubes, with 3 parallel samples for each material. 20 mL of the prepared arsenic ion solution was slowly poured into the centrifuge tubes to conduct the material adsorption experiment. The material addition amount was 0.1 g / L. The concentration of the solution after adsorption equilibrium was measured after 24 hours to obtain the adsorption results of different materials for arsenic.

[0060] The rice husk biochar powders (RHB) obtained in Example 1 (S1), Comparative Example 1, and Comparative Example 2 were tested, and the results are as follows: Figure 6 As shown, the adsorption performance of the base materials at 300℃ and 500℃ is comparable under three different pyrolysis temperatures, with the base material at 500℃ showing greater potential in terms of performance.

[0061] The iron ions (eFh) contained in the rice husk biochar powder (RHB), oxygen-activated iron-rich biochar (OFRHB), and oxygen-activated iron-rich biochar (OFRHB) prepared in Example 1, and the ferrous sulfate (Fh) prepared in Comparative Example 5 were tested, and the test results are as follows: Figure 7As shown, the oxygen-activated iron-rich biochar (OFRHB) prepared using the method of this invention achieves an adsorption rate of 90%, demonstrating good adsorption performance and high material utilization efficiency. Under the same conditions, the adsorption performance of the oxygen-activated iron-rich biochar of this invention (OFRHB, 90.4% arsenic adsorption rate) is consistently higher than that of simple biochar (RHB, 5% arsenic adsorption rate) and ferrohydrate (Fh, 75.2% arsenic adsorption rate). Furthermore, the adsorption performance of the equivalent iron in the oxygen-activated iron-rich biochar is significantly lower than its own content, indicating that the adsorption performance of the oxygen-activated iron-rich biochar mainly originates from the contributions of ferrohydrate and the oxygen-activated base material.

[0062] The rice husk biochar powder (RHB) prepared in Example 1, the oxygen-carrying biochar (ORHB) prepared in Comparative Example 4, the iron-rich biochar (FRHB) prepared in Comparative Example 3, and the oxygen-activated iron-rich biochar (OFRHB, OFRBB) obtained in Examples 1-3 were tested, and the test results are as follows: Figure 8 As shown, the adsorption performance of oxygen-activated iron-rich biochar is also higher than that of oxygen-loaded biochar (ORHB, 5% arsenic adsorption rate) and iron-rich biochar (FRHB, 78.8% arsenic adsorption rate). Oxygen-loaded biochar has a very small effect on improving the adsorption performance of rice husk biochar, while iron-rich biochar has a significant effect on improving the adsorption performance of rice husk biochar. Oxygen activation further improves the adsorption performance of iron-rich biochar. At the same time, oxygen-activated iron-rich biochar made from rice husk has the best adsorption performance, which is better than that of rice straw and wheat straw.

[0063] The adsorption performance of rice husk biochar powder (RHB) prepared in Example 1 and oxygen-activated iron-rich biochar (OFRHB) obtained in Examples 4, 5, and 6, as well as ferrous sulfate (Fh) obtained in Comparative Example 5, was tested. The adsorption results of materials with different iron salt contents for arsenic were obtained as shown in the bar graphs. Figure 9 As shown, the adsorption performance of oxygen-activated iron-rich biochar is optimal when the mass ratio of raw biochar powder to ferric nitrate nonahydrate powder particles is 1:5, i.e., the carbon-iron ratio is 10:7.

[0064] Figure 10 This diagram illustrates the adsorption efficiency and contribution rate of each component in the oxygen-activated iron-rich biochar prepared in Example 1. Under conditions of equal amounts of iron ions, the arsenic adsorption rates of the rice husk biochar powder and the oxygen-activated iron-rich biochar prepared in Example 1 were 5% and 41.67%, respectively. The arsenic adsorption rate of the oxygen-carrying biochar obtained in Comparative Example 4 shows that the contribution rate of oxygen to adsorption is comparable to that of the rice husk biochar powder. Based on the arsenic adsorption rate of the oxygen-activated iron-rich biochar obtained in Example 1, the adsorption contribution rate of an equal amount of iron ions was 47.8%, therefore the adsorption contribution rate of the high-purity oxygen-activated base material was 52.2%.

[0065] By using high-purity oxygen to optimize iron-rich biochar, the material's specific surface area increases, average pore size decreases, and the number of micropores increases, further enhancing the contact area between the material and heavy metal ions in solution systems. The increased number of effective functional groups significantly improves adsorption capacity. The high-purity oxygen activation process is simple, low-cost, and low-energy-consumption. The raw materials used in this invention are all derived from nature and returned to nature, showing broad application prospects for the remediation of wastewater, contaminated soil, and polluted farmland soil, especially for the remediation of metals in paddy fields and their irrigation water, ensuring agricultural product safety, increasing carbon sequestration in farmland, and reducing carbon emissions.

[0066] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing oxygen-activated iron-rich biochar, characterized in that, Includes the following steps: S1: After crushing the biomass raw material, it is first sieved to obtain sieved biomass raw material. Under anaerobic conditions, the sieved biomass raw material is subjected to high-temperature pyrolysis, cooled, and then sieved a second time to obtain raw biochar powder. S2: The raw biochar powder and ferric nitrate nonahydrate are mixed and stirred in deionized water to obtain a first solution. Then, KOH solution is added under the condition of oxygen introduction to obtain a second solution. The second solution is washed with deionized water until the pH value of the second solution is 6.9~7.

1. Then, the second solution is centrifuged or allowed to stand to precipitate for solid-liquid separation to obtain a precipitated solid. The precipitated solid is freeze-dried and finally subjected to a third sieve to obtain oxygen-activated iron-rich biochar. The mass ratio of the raw biochar powder to ferric nitrate nonahydrate is 1:1 to 1:10; the mass ratio of the raw biochar powder to deionized water is 1:

50.

2. The preparation method according to claim 1, characterized in that, In step S1 The biomass raw materials are selected from corn stalks, wheat stalks, bamboo, wood, rice stalks, and rice husks; The mesh size of the sieve used in the first sieve is 100~200 mesh.

3. The preparation method according to claim 1, characterized in that, The oxygen-deficient condition in step S1 specifically refers to an environment where air is isolated and no gas is introduced.

4. The preparation method according to claim 1, characterized in that, In step S1, the high-temperature pyrolysis temperature is 300℃~700℃; the high-temperature pyrolysis time is 2~3 h; and the high-temperature pyrolysis heating rate is 5~10℃ / min.

5. The preparation method according to claim 1, characterized in that, In step S1, the cooling temperature is 20℃~25℃; the cooling time is 2h~24h. The mesh size of the sieve used for the second sieve is 100-200 mesh.

6. The preparation method according to claim 1, characterized in that, In step S2, the mixing and stirring time is 1~10h; the partial pressure of the oxygen gas is 0.05~0.2 MPa; the flow rate of the oxygen is 8~15 L / min; and the purity of the oxygen is greater than 99wt%.

7. The preparation method according to claim 1, characterized in that, In step S2, The concentration of the KOH solution is 2~3 mol / L.

8. The preparation method according to claim 1, characterized in that, In step S2, pre-freezing is performed before freeze-drying; The pre-freezing temperature is -18℃ to -24℃; the pre-freezing time is 2 to 30 hours. The sample temperature during freeze-drying is 20℃ to -40℃, the cold trap temperature is -40℃ to -80℃, and the vacuum pressure is 1 to 60 Pa; the freeze-drying time is 2 to 7 days. The mesh size of the sieve used in the third sieve is 100-200 mesh.

9. An oxygen-activated iron-rich biochar prepared by the preparation method according to any one of claims 1 to 8.

10. The application of the oxygen-activated iron-rich biochar of claim 9 in the remediation of arsenic-contaminated soil and / or water.

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