Iron-manganese oxide with carbon sequestration capability as well as preparation method and application of iron-manganese oxide

Abstract

The invention relates to the technical field of soil improvement, in particular to an iron and manganese oxide with carbon sequestration capacity and a preparation method and application thereof. The preparation method of the iron and manganese oxide comprises the following steps: dissolving soluble trivalent iron salt and soluble divalent manganese salt in water to obtain a mixed salt solution, adding an alkaline precipitator into the mixed salt solution to adjust the pH value, carrying out a stirring reaction, obtaining a precipitate suspension after the reaction is ended, carrying out an aging oxidation reaction on the suspension, and centrifuging after the reaction is ended to obtain the iron and manganese oxide. Washing, freeze-drying, grinding and sieving the obtained precipitate to obtain iron and manganese oxides with carbon sequestration capacity; wherein the aging oxidation temperature is 30-40 DEG C, and the aging oxidation time is 45-50 hours. The iron and manganese oxide prepared by chemical coprecipitation and mild oxidation aging processes has the characteristics of high specific surface area and high surface activity, has the DOM immobilization capability far better than that of natural iron oxide and manganese mineral, and can significantly improve the soil carbon sequestration capability.

Description

Technical Field

[0001] This invention relates to the field of soil improvement technology, specifically to an iron-manganese oxide with carbon fixation capabilities, its preparation method, and its application. Background Technology

[0002] Soil is the largest organic carbon pool in terrestrial ecosystems, and even small changes in it can significantly affect atmospheric CO2 concentrations. Stabilizing and enhancing soil organic carbon pools, i.e., strengthening soil carbon sequestration function, is one of the key approaches to addressing climate change.

[0003] Natural iron oxides and manganese oxides are important active components in soil. They can form stable organic-mineral complexes with soil organic matter (especially dissolved organic matter, DOM) through adsorption, co-precipitation, and catalytic polymerization, thereby protecting organic carbon from microbial decomposition. However, natural iron oxides and manganese oxides have the following limitations: ① Limited activity: high crystallinity, small specific surface area, and insufficient reactive sites; ② Poor stability: easily reduced and dissolved under anaerobic conditions, leading to the re-release of fixed organic carbon; ③ Uncontrollable efficiency: their content and form distribution in natural soils are uneven, making it impossible to maximize their carbon sequestration effect.

[0004] Therefore, developing a method for preparing iron-manganese oxide materials with high activity, high stability, and the ability to directionally enhance soil carbon sequestration has significant practical application value. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides an iron-manganese oxide with carbon fixation capabilities, its preparation method, and its application. The iron-manganese oxide prepared by this invention through a process of chemical co-precipitation and mild oxidative aging has the characteristics of high specific surface area and high surface activity. Its carbon fixation capacity for DOM far exceeds that of natural iron oxides and manganese minerals, and it can significantly improve the soil's carbon fixation capacity.

[0006] Therefore, the present invention provides the following technical solution:

[0007] In a first aspect, the present invention provides, in optional embodiments, a method for preparing an iron-manganese oxide with carbon-fixing ability, comprising the following steps:

[0008] Soluble ferric salt and soluble manganese salt are dissolved in water to obtain a mixed salt solution. An alkaline precipitant is added to the mixed salt solution to adjust the pH and the mixture is stirred. After the reaction is completed, a precipitate suspension is obtained. The suspension is subjected to an aging oxidation reaction. After the reaction is completed, the mixture is centrifuged, and the obtained precipitate is washed, freeze-dried, ground, and sieved to obtain iron and manganese oxides with carbon fixation ability.

[0009] The aging oxidation is carried out at a temperature of 30-40°C for 45-50 hours.

[0010] Preferably, in the mixed salt solution, the Fe 3+ and Mn 2+ The molar ratio is 1-5:1; and / or, the soluble trivalent iron salt is selected from one or more of ferric chloride hexahydrate, ferric nitrate nonahydrate, and ferric sulfate pentahydrate; and / or, the soluble divalent manganese salt is selected from one or more of manganese chloride tetrahydrate, manganese nitrate tetrahydrate, and manganese sulfate tetrahydrate.

[0011] Furthermore, in the mixed salt solution, the Fe 3+ and Mn 2+ The molar ratio is 4:1; and / or, the soluble trivalent iron salt is selected from ferric chloride hexahydrate; and / or, the soluble divalent manganese salt is selected from manganese chloride tetrahydrate.

[0012] Preferably, the rate at which the alkaline precipitant is added to the mixed salt solution is 2 mL / min; and / or, the alkaline precipitant is one or a mixture of sodium hydroxide solution and potassium hydroxide solution; and / or, the concentration of the alkaline precipitant is 1-5 mol / L. The pH is 8-10; and / or, the stirring reaction time is 2-4 hours. The centrifugation speed is 4500-5500 rpm; and / or, the freeze-drying temperature is -45°C; and / or, the sieve mesh size is 200 mesh.

[0013] Secondly, in an optional embodiment, the present invention provides an iron-manganese oxide with carbon fixation capability, which is prepared by the above-described preparation method.

[0014] Preferably, the iron-manganese oxide has a weakly crystalline state; and / or, the specific surface area of ​​the iron-manganese oxide is 190-290 m². 2 / g.

[0015] The iron-manganese oxide material prepared by this invention has the following characteristics:

[0016] Phase structure: It is mainly in a weakly crystalline state, with characteristic structures containing ferrohydrate and Mn(III / IV) (hydrogen) oxides.

[0017] Microstructure: Under a transmission electron microscope, it appears as a porous aggregate with a high specific surface area formed by the aggregation of nano-sized particles.

[0018] High reactivity: Possesses a large specific surface area (≥190 m²) 2 It has abundant surface hydroxyl functional groups ( / g) and exhibits significant adsorption and fixation capabilities for soluble organic matter.

[0019] In this invention, compared to single iron oxides, iron-manganese oxides have the following advantages in carbon fixation:

[0020] 1. Oxidative polymerization:

[0021] One of the key advantages of iron-manganese oxides is their ability to convert unstable carbon into stable carbon.

[0022] Single iron oxides (such as goethite and ferrihydrite): Their main mechanisms of action are adsorption and co-precipitation. They fix dissolved organic matter through surface coordination, forming an "iron-organic matter" complex, which physically isolates microorganisms. However, this is essentially a physical constraint, and the chemical structure of the fixed organic matter does not change much.

[0023] Iron-manganese oxides: Manganese (Mn(III / IV)) in these oxides has oxidizing capabilities. It can not only adsorb DOM (dimethylformamide) but also catalyze the oxidation of DOM molecules, causing them to polymerize and form larger, more complex, and more inert high-molecular-weight organic compounds (similar to the formation of humic substances). This "chemical transformation" process converts easily decomposed small-molecule organic compounds into complex aromatic polymers that are difficult for microbial enzymes to attack, fundamentally improving the chemical stability of organic matter.

[0024] Analogy: single iron oxide is like a "cage" that locks in organic carbon; while iron-manganese oxide is not only a "cage" but also a "chemical plant" that processes the "fresh meat" (easily decomposable carbon) inside into "cured meat" (difficult-to-decompose carbon), greatly extending its shelf life.

[0025] 2. Formation of more stable ternary complexes

[0026] Single iron oxides: primarily form iron-organic binary complexes. Iron-manganese oxides: can form manganese-organic-iron ternary complexes. DOM can first be oxidized by manganese oxides, and the product then binds to iron oxides through stronger bonding (such as inner-layer complexes). This "bridging" effect creates more and stronger chemical bonds, making the organic matter more firmly "locked" in, and far more difficult to dissociate and release than binary complexes.

[0027] 3. Self-repair in redox cycles and the potential for carbon refixation

[0028] Redox conditions in soil are dynamic (e.g., alternating wet and dry periods). Single iron oxides: Under anaerobic conditions, they are reduced to soluble Fe(II), leading to a large release of fixed organic carbon and reversing carbon fixation. Iron-manganese oxides: Microorganisms and organic matter typically preferentially reduce manganese oxides (Mn(III / IV) to Mn(II)) before reducing iron oxides. This provides a "buffer period" for iron oxides, protecting them during brief anaerobic conditions. When the environment returns to aerobic conditions, the released Mn(II) and Fe(II) are rapidly reoxidized, forming new iron-manganese oxide precipitates. These newly generated iron-manganese oxides are highly reactive, immediately capturing and fixing surrounding released DOM, achieving "self-regeneration" of carbon fixation capacity. The regenerative capacity and efficiency of single iron systems are typically lower.

[0029] Compared to single manganese oxides, iron-manganese oxides have the following advantages in carbon fixation:

[0030] 1. More diverse carbon fixation mechanisms, covering a wider range of organic carbon types.

[0031] Manganese oxides primarily fix carbon through oxidative polymerization, oxidizing easily decomposable small-molecule organic carbon (such as organic acids) in the soil into more stable large-molecule carbon, thus limiting their applicability. Iron-manganese oxides, however, possess both core mechanisms: ① Manganese oxidation: continuing the advantages of manganese oxides by oxidizing and polymerizing small-molecule organic carbon. ② Iron adsorption: iron (especially amorphous iron) has extremely strong adsorption capacity, adsorbing both large and small-molecule organic matter in the soil, and even combining with particulate organic carbon or microbial residues, covering a far wider range of organic carbon types than manganese oxides alone.

[0032] 2. It has stronger carbon sequestration stability and greater resistance to environmental disturbances.

[0033] Changes in soil pH and redox potential significantly affect the carbon fixation efficiency of single manganese oxides. For example, in strongly reducing environments, manganese is easily reduced and dissolved, leading to a substantial decrease in carbon fixation capacity. In iron-manganese oxides, the presence of iron forms a "buffer barrier." Iron is chemically more stable and is less prone to dissolution and loss under complex soil conditions such as acidic and reducing environments. Iron and manganese can form composite structures (such as iron-manganese nodules), which not only protect manganese from easy reduction but also maintain the activity of their own adsorption sites, making the carbon fixation effect more stable in different soil environments.

[0034] 3. It has higher carbon fixation efficiency and can form a stable "manganese-carbon-iron" complex.

[0035] Single manganese oxides primarily alter the chemical form of organic carbon through oxidation reactions; however, organic carbon may still be lost during carbon fixation due to microbial decomposition or leaching. Iron-manganese oxides, through a synergistic effect of oxidation and adsorption, form a more difficult-to-decompose ternary complex of manganese, carbon, and iron.

[0036] First, manganese oxides oxidize and polymerize small-molecule organic carbon to improve its stability. Then, iron oxides firmly adsorb the oxidized organic carbon onto their own surface, or even encapsulate it inside the iron-manganese oxides. This dual approach of physical and chemical means blocks the decomposition pathway of organic carbon, resulting in a significantly higher carbon fixation efficiency compared to manganese oxides alone.

[0037] Thirdly, in optional embodiments, the present invention provides the application of the aforementioned iron-manganese oxide with carbon sequestration capability as a soil sinking agent in farmland soil carbon sequestration, degraded soil remediation, and soil carbon pool protection.

[0038] Preferably, the pH of the soil is 4.9-8.3.

[0039] Compared with the prior art, the present invention has one of the following beneficial effects:

[0040] 1. The iron-manganese oxide prepared by the present invention through chemical co-precipitation and mild oxidative aging process has the characteristics of high specific surface area and high surface activity. Its ability to retain DOM far exceeds that of natural iron oxide and manganese oxide, and can significantly improve the soil carbon sequestration capacity.

[0041] 2. The iron-manganese oxide provided by this invention has better chemical stability in soil redox fluctuations than single iron oxides or manganese oxides, and can exert its carbon fixation function for a longer period of time.

[0042] 3. The iron-manganese oxide provided by this invention is derived from natural sources and poses no environmental risk when applied to the soil. Furthermore, it can improve soil structure, enhance soil fertility, and ensure soil health through multiple pathways, including carbon fixation and the provision of trace iron and manganese elements.

[0043] 4. The iron-manganese oxide provided by this invention uses inexpensive and readily available raw materials, and the preparation process does not require high-temperature and high-pressure equipment, has low energy consumption, is suitable for large-scale production, and has good market promotion prospects. Attached Figure Description

[0044] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0045] Figure 1These are transmission electron micrographs of the iron-manganese oxides in Examples 1-5, wherein... Figure 1 (a) is a transmission electron microscope image of the Fe / Mn oxide (Fe / Mn = 1:1) in Example 1. Figure 1 (b) is a transmission electron microscope image of the iron-manganese oxide Fe / Mn=2:1 in Example 2. Figure 1 (c) is a transmission electron microscope image of the iron-manganese oxide Fe / Mn=3:1 in Example 3. Figure 1 (d) is a transmission electron microscope image of the iron-manganese oxide Fe / Mn=4:1 in Example 4. Figure 1 (e) is a transmission electron microscope image of the iron-manganese oxide Fe / Mn=5:1 in Example 5;

[0046] Figure 2 This is a schematic diagram showing the specific surface area results of iron-manganese oxides in Examples 1-5;

[0047] Figure 3 The X-ray diffraction patterns of the iron-manganese oxides in Examples 1-5 are shown below.

[0048] Figure 4 This is a schematic diagram showing the zero-charge point results of iron-manganese oxides in Examples 1-5;

[0049] Figure 5 The X-ray photoelectron spectra of Fe 2p iron-manganese oxide in Examples 1-5 are shown.

[0050] Figure 6 This is a schematic diagram showing the percentage of Fe valence states in iron-manganese oxides in Examples 1-5;

[0051] Figure 7 The X-ray photoelectron spectra of iron-manganese oxide Mn 2p in Examples 1-5 are shown below.

[0052] Figure 8 This is a schematic diagram showing the proportion of Mn valence states in iron-manganese oxides in Examples 1-5;

[0053] Figure 9 The X-ray photoelectron spectra of iron-manganese oxide O 1s in Examples 1-5 are shown below.

[0054] Figure 10 This is a schematic diagram showing the proportion of oxygen forms in iron-manganese oxides in Examples 1-5;

[0055] Figure 11 This is a schematic diagram showing the test results of the organic carbon sequestration performance of iron-manganese oxides in Experiment Example 2. Figure 11 (a) represents the concentration of dissolved organic carbon in the solution phase after adsorption equilibrium. Figure 11 (b) represents the concentration of organic carbon on the solid phase after the reaction;

[0056] Figure 12The results show the stability test results of the iron-manganese oxide fixation of organic carbon in Experiment Example 3. Figure 12 (a) Figure 12 (b) Figure 12 (c) Schematic diagrams representing the results of experiments using soil samples taken from Changsha, Hunan Province (pH=4.9), Shaoguan, Guangdong Province (pH=6.7), and Shantou, Guangdong Province (pH=8.3), respectively;

[0057] Figure 13 This is a distribution diagram of the relative abundance of organic matter molecular weight on iron-manganese oxides in Experiment Example 4;

[0058] Figure 14 This is a graph showing the abundance percentage of high molecular weight organic matter (600-800 Da) on iron-manganese oxides in Experiment Example 4. Detailed Implementation

[0059] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0060] The technical solution of the present invention will be described below with reference to embodiments.

[0061] Example 1

[0062] This embodiment provides a method for preparing iron-manganese oxide with carbon fixation capability, including the following steps:

[0063] In this embodiment, iron-manganese oxide with an iron-manganese molar ratio of 1:1 was prepared.

[0064] S1. Weigh 5.406 g FeCl3·6H2O and 3.958 g MnCl2·4H2O into a 500 mL beaker, add 200 mL of pure water, place the beaker on a magnetic stirrer, add a magnetic stir bar, and stir the solution at 220 rpm for 10 min to obtain a mixed salt solution.

[0065] S2. Add sodium hydroxide solution (concentration is 1 mol / L) dropwise to the mixed salt solution at a rate of 2 mL / min. The color of the mixed solution gradually turns brownish and becomes turbid. Continue to add the solution dropwise until the pH of the suspension rises to 9.0. Stir continuously for 4 h, and control the pH of the suspension to maintain at 9.0±0.1 during the process to obtain a precipitated suspension.

[0066] S3. The above-mentioned precipitated suspension is aged at 35°C for 48 hours. During this period, air is introduced into the suspension at a flow rate of 2 L / min for gentle oxidation, promoting the formation of highly active, weakly crystalline iron-manganese oxides.

[0067] S4. Transfer the above suspension to a 50 mL centrifuge tube and centrifuge at 5000 rpm to separate the solid and liquid. Discard the supernatant after centrifugation, then add the same volume of pure water, mix thoroughly, centrifuge again, and discard the supernatant. Repeat this step 3-5 times to remove excess salt. Finally, freeze-dry the solid precipitate in the centrifuge tube (at -45℃), then grind it through a 200-mesh sieve to obtain powdered iron-manganese oxide with a molar ratio of 1:1, denoted as Fe / Mn=1:1.

[0068] Example 2

[0069] This embodiment provides a method for preparing iron-manganese oxide with carbon fixation capability, including the following steps:

[0070] In this embodiment, iron-manganese oxide with an iron-manganese molar ratio of 2:1 was prepared.

[0071] S1. Weigh 5.406 g FeCl3·6H2O and 1.979 g MnCl2·4H2O into a 500 mL beaker, add 200 mL of pure water, place the beaker on a magnetic stirrer, add a magnetic stir bar, and stir the solution at 220 rpm for 10 min to obtain a mixed salt solution.

[0072] S2. Add sodium hydroxide solution (concentration is 1 mol / L) dropwise to the mixed salt solution at a rate of 2 mL / min. The color of the mixed solution gradually turns brownish and becomes turbid. Continue to add the solution dropwise until the pH of the suspension rises to 9.0. Stir continuously for 4 h, and control the pH of the suspension to maintain at 9.0±0.1 during the process to obtain a precipitated suspension.

[0073] S3. The above-mentioned precipitated suspension is aged at 35°C for 48 hours. During this period, air is introduced into the suspension at a flow rate of 2 L / min for gentle oxidation, promoting the formation of highly active, weakly crystalline iron-manganese oxides.

[0074] S4. Transfer the above suspension to a 50 mL centrifuge tube and centrifuge at 5000 rpm to separate the solid and liquid. Discard the supernatant after centrifugation, then add the same volume of pure water, mix thoroughly, centrifuge again, and discard the supernatant. Repeat this step 3-5 times to remove excess salt. Finally, freeze-dry the solid precipitate in the centrifuge tube (at -45℃), then grind it through a 200-mesh sieve to obtain powdered iron-manganese oxide with a molar ratio of 2:1, denoted as Fe / Mn=2:1.

[0075] Example 3

[0076] This embodiment provides a method for preparing iron-manganese oxide with carbon fixation capability, including the following steps:

[0077] In this embodiment, iron-manganese oxide with an iron-manganese molar ratio of 3:1 was prepared.

[0078] S1. Weigh 5.406 g FeCl3·6H2O and 1.319 g MnCl2·4H2O into a 500 mL beaker, add 200 mL of pure water, place the beaker on a magnetic stirrer, add a magnetic stir bar, and stir the solution at 220 rpm for 10 min to obtain a mixed salt solution.

[0079] S2. Add sodium hydroxide solution (concentration is 1 mol / L) dropwise to the mixed salt solution at a rate of 2 mL / min. The color of the mixed solution gradually turns brownish and becomes turbid. Continue to add the solution dropwise until the pH of the suspension rises to 9.0. Stir continuously for 4 h, and control the pH of the suspension to maintain at 9.0±0.1 during the process to obtain a precipitated suspension.

[0080] S3. The above-mentioned precipitated suspension is aged at 35°C for 48 hours. During this period, air is introduced into the suspension at a flow rate of 2 L / min for gentle oxidation, promoting the formation of highly active, weakly crystalline iron-manganese oxides.

[0081] S4. Transfer the above suspension to a 50 mL centrifuge tube and centrifuge at 5000 rpm to separate the solid and liquid. Discard the supernatant after centrifugation, then add the same volume of pure water, mix thoroughly, centrifuge again, and discard the supernatant. Repeat this step 3-5 times to remove excess salt. Finally, freeze-dry the solid precipitate in the centrifuge tube (at -45℃), then grind it through a 200-mesh sieve to obtain powdered iron-manganese oxide with a molar ratio of 3:1, denoted as Fe / Mn=3:1.

[0082] Example 4

[0083] This embodiment provides a method for preparing iron-manganese oxide with carbon fixation capability, including the following steps:

[0084] In this embodiment, iron-manganese oxide with an iron-manganese molar ratio of 4:1 was prepared.

[0085] S1. Weigh 5.406 g FeCl3·6H2O and 0.989 g MnCl2·4H2O into a 500 mL beaker, add 200 mL of pure water, place the beaker on a magnetic stirrer, add a magnetic stir bar, and stir the solution at 220 rpm for 10 min to obtain a mixed salt solution.

[0086] S2. Add sodium hydroxide solution (concentration is 1 mol / L) dropwise to the mixed salt solution at a rate of 2 mL / min. The color of the mixed solution gradually turns brownish and becomes turbid. Continue to add the solution dropwise until the pH of the suspension rises to 9.0. Stir continuously for 4 h, and control the pH of the suspension to maintain at 9.0±0.1 during the process to obtain a precipitated suspension.

[0087] S3. The above-mentioned precipitated suspension is aged at 35°C for 48 hours. During this period, air is introduced into the suspension at a flow rate of 2 L / min for gentle oxidation, promoting the formation of highly active, weakly crystalline iron-manganese oxides.

[0088] S4. Transfer the above suspension to a 50 mL centrifuge tube and centrifuge at 5000 rpm to separate the solid and liquid. Discard the supernatant after centrifugation, then add the same volume of pure water, mix thoroughly, centrifuge again, and discard the supernatant. Repeat this step 3-5 times to remove excess salt. Finally, freeze-dry the solid precipitate in the centrifuge tube (at -45℃), then grind it through a 200-mesh sieve to obtain powdered iron-manganese oxide with a molar ratio of 4:1, denoted as Fe / Mn=4:1.

[0089] Example 5

[0090] This embodiment provides a method for preparing iron-manganese oxide with carbon fixation capability, including the following steps:

[0091] In this embodiment, iron-manganese oxide with an iron-manganese molar ratio of 5:1 was prepared.

[0092] S1. Weigh 5.406 g FeCl3·6H2O and 0.792 g MnCl2·4H2O into a 500 mL beaker, add 200 mL of pure water, place the beaker on a magnetic stirrer, add a magnetic stir bar, and stir the solution at 220 rpm for 10 min to obtain a mixed salt solution.

[0093] S2. Add sodium hydroxide solution (concentration is 1 mol / L) dropwise to the mixed salt solution at a rate of 2 mL / min. The color of the mixed solution gradually turns brownish and becomes turbid. Continue to add the solution dropwise until the pH of the suspension rises to 9.0. Stir continuously for 4 h, and control the pH of the suspension to maintain at 9.0±0.1 during the process to obtain a precipitated suspension.

[0094] S3. The above-mentioned precipitated suspension is aged at 35°C for 48 hours. During this period, air is introduced into the suspension at a flow rate of 2 L / min for gentle oxidation, promoting the formation of highly active, weakly crystalline iron-manganese oxides.

[0095] S4. Transfer the above suspension to a 50 mL centrifuge tube and centrifuge at 5000 rpm to separate the solid and liquid. Discard the supernatant after centrifugation, then add the same volume of pure water, mix thoroughly, centrifuge again, and discard the supernatant. Repeat this step 3-5 times to remove excess salt. Finally, freeze-dry the solid precipitate in the centrifuge tube (at -45℃), then grind it through a 200-mesh sieve to obtain powdered iron-manganese oxide with a molar ratio of 5:1, denoted as Fe / Mn=5:1.

[0096] Comparative Example 1

[0097] This comparative example provides a method for preparing iron-manganese oxide with carbon fixation capability, comprising the following steps:

[0098] This comparative example prepared iron-manganese oxide with an iron-manganese molar ratio of 4:1.

[0099] S1. Weigh 5.406 g FeCl3·6H2O and 0.989 g MnCl2·4H2O into a 500 mL beaker, add 200 mL of pure water, place the beaker on a magnetic stirrer, add a magnetic stir bar, and stir the solution at 220 rpm for 10 min to obtain a mixed salt solution.

[0100] S2. Add sodium hydroxide solution (concentration is 1 mol / L) dropwise to the mixed salt solution at a rate of 2 mL / min. The color of the mixed solution gradually turns brownish and becomes turbid. Continue to add the solution dropwise until the pH of the suspension rises to 9.0. Stir continuously for 4 h, and control the pH of the suspension to maintain at 9.0±0.1 during the process to obtain a precipitated suspension.

[0101] S3. Transfer the above suspension to a 50 mL centrifuge tube and centrifuge at 5000 rpm to achieve solid-liquid separation. Discard the supernatant after centrifugation, then add the same volume of pure water, mix thoroughly, centrifuge again, and discard the supernatant. Repeat this step 3-5 times to remove excess salt. Subsequently, transfer the solid precipitate in the centrifuge tube to a crucible and sinter it in a muffle furnace at 650℃ for 6 h. After cooling, grind it through a 200-mesh sieve to obtain powdered iron-manganese oxide, denoted as Fe / Mn=4:1 (650℃).

[0102] Comparative Example 2

[0103] This comparative example provides a method for preparing iron-manganese oxide with carbon fixation capability, comprising the following steps:

[0104] This comparative example prepared iron-manganese oxide with an iron-manganese molar ratio of 4:1.

[0105] S1. Weigh 5.406 g FeCl3·6H2O and 0.989 g MnCl2·4H2O into a 500 mL beaker, add 200 mL of pure water, place the beaker on a magnetic stirrer, add a magnetic stir bar, and stir the solution at 220 rpm for 10 min to obtain a mixed salt solution.

[0106] S2. Add sodium hydroxide solution (concentration is 1 mol / L) dropwise to the mixed salt solution at a rate of 2 mL / min. The color of the mixed solution gradually turns brownish and becomes turbid. Continue to add the solution dropwise until the pH of the suspension rises to 9.0. Stir continuously for 4 h, and control the pH of the suspension to maintain at 9.0±0.1 during the process to obtain a precipitated suspension.

[0107] S3. Transfer the above precipitate suspension to a reaction vessel and react at 180℃ for 6 h. Then transfer the suspension to a centrifuge tube and separate the solid and liquid at 5000 rpm. Discard the supernatant after centrifugation, add the same volume of pure water, mix thoroughly, centrifuge again, and discard the supernatant. Repeat this step 3-5 times to remove excess salt. Then age at room temperature for 4 hours, obtain a solid precipitate by centrifugation, dry it in a 60℃ oven, and finally grind it through a 200-mesh sieve to obtain powdered iron-manganese oxide with a molar ratio of 4:1, denoted as Fe / Mn=4:1 (180℃).

[0108] Comparative Example 3

[0109] This comparative example provides a method for preparing iron-manganese oxide with carbon fixation capability, comprising the following steps:

[0110] This comparative example prepared iron-manganese oxide with an iron-manganese molar ratio of 4:1.

[0111] S1. Weigh 5.406 g FeCl3·6H2O and 0.989 g MnCl2·4H2O into a 500 mL beaker, add 200 mL of pure water, place the beaker on a magnetic stirrer, add a magnetic stir bar, and stir the solution at 220 rpm for 10 min to obtain a mixed salt solution.

[0112] S2. Add sodium hydroxide solution (concentration is 1 mol / L) dropwise to the mixed salt solution at a rate of 2 mL / min. The color of the mixed solution gradually turns brownish and becomes turbid. Continue to add the solution dropwise until the pH of the suspension rises to 9.0. Stir continuously for 4 h, and control the pH of the suspension to maintain at 9.0±0.1 during the process to obtain a precipitated suspension.

[0113] S3. The above-mentioned precipitated suspension is aged at 25°C for 48 hours. During this period, air is introduced into the suspension at a flow rate of 2 L / min for gentle oxidation, promoting the formation of highly active, weakly crystalline iron-manganese oxides.

[0114] S4. Transfer the above suspension to a 50 mL centrifuge tube and centrifuge at 5000 rpm to separate the solid and liquid. Discard the supernatant after centrifugation, then add the same volume of pure water, mix thoroughly, centrifuge again, and discard the supernatant. Repeat this step 3-5 times to remove excess salt. Finally, freeze-dry the solid precipitate in the centrifuge tube (at -45℃), then grind it through a 200-mesh sieve to obtain powdered iron-manganese oxide with a molar ratio of 4:1, denoted as Fe / Mn=4:1 (25℃).

[0115] Comparative Example 4

[0116] This comparative example provides a method for preparing iron-manganese oxide with carbon fixation capability, comprising the following steps:

[0117] This comparative example prepared iron-manganese oxide with an iron-manganese molar ratio of 4:1.

[0118] S1. Weigh 5.406 g FeCl3·6H2O and 0.989 g MnCl2·4H2O into a 500 mL beaker, add 200 mL of pure water, place the beaker on a magnetic stirrer, add a magnetic stir bar, and stir the solution at 220 rpm for 10 min to obtain a mixed salt solution.

[0119] S2. Add sodium hydroxide solution (concentration is 1 mol / L) dropwise to the mixed salt solution at a rate of 2 mL / min. The color of the mixed solution gradually turns brownish and becomes turbid. Continue to add the solution dropwise until the pH of the suspension rises to 9.0. Stir continuously for 4 h, and control the pH of the suspension to maintain at 9.0±0.1 during the process to obtain a precipitated suspension.

[0120] S3. The above precipitated suspension is aged at 45°C for 48 hours. During this period, air is introduced into the suspension at a flow rate of 2 L / min for gentle oxidation, promoting the formation of highly active, weakly crystalline iron-manganese oxides.

[0121] S4. Transfer the above suspension to a 50 mL centrifuge tube and centrifuge at 5000 rpm to separate the solid and liquid. Discard the supernatant after centrifugation, then add the same volume of pure water, mix thoroughly, centrifuge again, and discard the supernatant. Repeat this step 3-5 times to remove excess salt. Finally, freeze-dry the solid precipitate in the centrifuge tube (at -45℃), then grind it through a 200-mesh sieve to obtain powdered iron-manganese oxide with a molar ratio of 4:1, denoted as Fe / Mn=4:1 (45℃).

[0122] Comparative Example 5

[0123] This comparative example provides a method for preparing iron-manganese oxide with carbon fixation capability, comprising the following steps:

[0124] This comparative example prepared iron-manganese oxide with an iron-manganese molar ratio of 4:1.

[0125] S1. Weigh 5.406 g FeCl3·6H2O and 0.989 g MnCl2·4H2O into a 500 mL beaker, add 200 mL of pure water, place the beaker on a magnetic stirrer, add a magnetic stir bar, and stir the solution at 220 rpm for 10 min to obtain a mixed salt solution.

[0126] S2. Add sodium hydroxide solution (concentration is 1 mol / L) dropwise to the mixed salt solution at a rate of 2 mL / min. The color of the mixed solution gradually turns brownish and becomes turbid. Continue to add the solution dropwise until the pH of the suspension rises to 9.0. Stir continuously for 4 h, and control the pH of the suspension to maintain at 9.0±0.1 during the process to obtain a precipitated suspension.

[0127] S3. The above-mentioned precipitated suspension is aged at 35°C for 48 hours. During this period, air is introduced into the suspension at a flow rate of 2 L / min for gentle oxidation, promoting the formation of highly active, weakly crystalline iron-manganese oxides.

[0128] S4. Transfer the above suspension to a 50 mL centrifuge tube and centrifuge at 5000 rpm to achieve solid-liquid separation. Discard the supernatant after centrifugation, then add the same volume of pure water, mix thoroughly, centrifuge again, and discard the supernatant. Repeat this step 3-5 times to remove excess salt. Finally, transfer the solid precipitate in the centrifuge tube to an oven for drying (at 60℃), then grind it through a 200-mesh sieve to obtain powdered iron-manganese oxide with a molar ratio of iron to manganese of 4:1, denoted as Fe / Mn=4:1 (60℃).

[0129] Experimental Example 1

[0130] Material characterization

[0131] The iron-manganese oxides prepared in Examples 1-5 were analyzed by transmission electron microscopy, specific surface area analysis, X-ray diffraction analysis, zero charge point analysis, and X-ray photoelectron spectroscopy. The specific methods are as follows:

[0132] 1) Transmission electron microscopy analysis

[0133] 0.01 g of the iron-manganese oxides prepared in Examples 1-5 were dispersed in anhydrous ethanol and sonicated with a constant-temperature water flow at 25°C for 30 minutes to ensure uniform dispersion. 30 µL of the sonicated suspension was dropped onto a lace carbon mesh supported by a 300-mesh copper mesh and dried under an infrared lamp for 10 min. The microstructure of the iron-manganese oxides was analyzed using a transmission electron microscope (FEITalos F200x), and the results are shown in [reference missing]. Figure 1 .

[0134] 2) Specific surface area analysis

[0135] 0.02 g of the iron-manganese oxides prepared in Examples 1-5 were placed in sample tubes, and the specific surface area of ​​the iron-manganese oxides was determined by N2 adsorption-desorption method using a specific surface area analyzer (NOVA4200e). The calculation method adopted was the Barrtt-Emmett-Teller (BET) algorithm. The results are shown in [reference needed]. Figure 2 .

[0136] 3) X-ray diffraction analysis

[0137] 0.1 g of the iron-manganese oxides prepared in Examples 1-5 were placed on the sample stage. The samples were flattened using a clean and smooth glass slide, and phase analysis was performed using an X-ray diffractometer (Bruker D8 ADVANCE). The test parameters were set as follows: tube voltage 40 kV, tube current 40 mA, scan speed 5° / min, step size 0.02°, and scan range 10°-80°. The results are shown in [reference needed]. Figure 3 .

[0138] 4) Zero-charge point analysis

[0139] The iron-manganese oxides prepared in Examples 1-5 were formulated into multiple 20 mg / L suspensions, and their pH values ​​were adjusted to 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, and 9.0, respectively. The suspensions were then ultrasonically dispersed, and their pH values ​​were confirmed using a pH meter. If any changes occurred, the pH values ​​were adjusted again to 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, and 9.0, respectively. The supernatant was collected, and its zero-charge point was analyzed using a zeta potential meter (Malvern, Nano ZS90). The results are shown in [reference needed]. Figure 4 .

[0140] 5) X-ray photoelectron spectroscopy analysis

[0141] X-ray photoelectron spectra of Fe 2p, Mn 2p, and O 1s in the iron-manganese oxides of Examples 1-5 were determined using an X-ray photoelectron spectrometer (Thermo Scientific K-Alpha). Before collecting the X-ray photoelectron spectra, the instrument was calibrated using the C1s binding energy to obtain accurate data. To quantify the valence states of Fe and Mn and the form of O in the iron-manganese oxides, the X-ray photoelectron spectra of Fe 2p, Mn 2p, and O 1s were fitted using Thermo Advantage software to obtain the percentage contents of Fe(III) and Fe(II), Mn(II), Mn(III), and Mn(IV), as well as the percentage contents of surface-adsorbed water (H₂O), surface hydroxyl oxygen (M-OH), and lattice oxygen (MO). The results are shown in [reference needed]. Figures 5-10 .

[0142] Conclusion: From Figure 1 It can be seen that the iron-manganese oxides in Examples 1-5 are porous aggregates formed by the aggregation of nanoscale particles. As the iron-manganese molar ratio increases, the number of fine particles of 1-3 nm gradually increases, while the number of short rod-shaped particles gradually decreases.

[0143] Depend on Figure 2 It can be seen that as the iron / manganese molar ratio increases, the specific surface area of ​​iron-manganese oxides gradually increases, from 193 m² when Fe / Mn = 1:1. 2 / g increased to 289 m at Fe / Mn=5:1 2 / g, but the rate of increase gradually decreases. When Fe / Mn=4:1, its specific surface area is close to that of Fe / Mn=5:1, which is 285 m². 2 / g.

[0144] Depend on Figure 3 It can be seen that the iron-manganese oxides in Examples 1-5 mainly exist as weakly crystalline phases, and the crystallinity of the iron-manganese oxides gradually decreases as the iron-manganese molar ratio increases.

[0145] Depend on Figure 4 It can be seen that as the iron-manganese molar ratio increases, the zero charge point of iron-manganese oxides gradually increases, from 5.6 for Fe / Mn=1:1 to 7.5 for Fe / Mn=5:1, but the rate of increase gradually decreases. When Fe / Mn=4:1, it is close to the zero charge point of Fe / Mn=5:1, which is 7.4.

[0146] Depend on Figure 5 and Figure 6 It can be seen that as the iron-manganese molar ratio increases, Fe exists as Fe(III).

[0147] Depend on Figure 7 and Figure 8It can be seen that as the iron-manganese molar ratio increases, Mn mainly exists as Mn(III) and Mn(IV), with contents of 41%-45% and 47%-52%, respectively.

[0148] Depend on Figure 9 and Figure 10 It can be seen that as the iron-manganese molar ratio increases, the proportion of M-OH gradually increases, from 42% in Fe / Mn=1:1 to 49% in Fe / Mn=5:1, but the rate of increase gradually decreases. When Fe / Mn=4:1, the proportion of M-OH is the same as that in Fe / Mn=5:1, which is 49%.

[0149] Experiment Example 2

[0150] (1) Extraction of dissolved organic matter from soil

[0151] Weigh 400 g of paddy soil into a 1000 mL PTFE bottle, add 400 mL of pure water, tighten the cap, and place the PTFE bottle in a shaker at 200 rpm for 24 h. After shaking, let the PTFE bottle stand for about 10 min, pour the supernatant into a centrifuge tube, and centrifuge at 5000 rpm. After centrifugation, filter the supernatant through a 0.45 µm filter membrane. The resulting filtrate is the soil dissolved organic matter (DOM) solution. The concentration of dissolved organic carbon was determined using a total organic carbon analyzer (vario TOC select, Elementar). The soil DOM solution was then diluted to 50 mg C / L and stored in a 4°C refrigerator protected from light for later use.

[0152] (2) Test on the retention performance of iron and manganese oxides on dissolved organic matter in soil

[0153] Take ten 1000 mL wide-mouth bottles, numbered 1-10, and add 500 mL of 50 mg C / L soil DOM solution to each. Then add 0.05 g of the iron-manganese oxides prepared in Examples 1-5 and Comparative Examples 1-5 to each bottle, and shake thoroughly to obtain a suspension. Adjust the pH of the suspension to 7.0 ± 0.2 with 0.1 mol / L HCl or 0.1 mol / L NaOH, tighten the caps, and place all the wide-mouth bottles in a shaker. Shake at 200 rpm for 24 h to allow the reaction to proceed completely.

[0154] The resulting suspension was transferred to a 50 mL centrifuge tube and centrifuged at 5000 rpm for 30 min. The supernatant was then filtered through a 0.45 μm filter membrane, and the filtrate was collected. The pH of the filtrate was adjusted to 2.0 with 1 mol HCl. The concentrations of dissolved organic carbon in the filtrate and organic carbon in the solid precipitate were determined using a total organic carbon analyzer (Vario TOC Select, Elementar). The results are shown below. Figure 11 .

[0155] Conclusion: From Figure 11 It can be seen that when the soil organic carbon sequestration performance was tested using the iron-manganese oxides prepared in Examples 1-5, the organic carbon concentration in the solution phase decreased from 33.1 mg C / L to 28.8 mg C / L in the Fe / Mn=1:1 to Fe / Mn=5:1 treatment groups, while the organic carbon concentration in the solid phase increased from 169 mg C / g to 212 mg C / g. This indicates that as the iron-manganese molar ratio increases, more active soil organic carbon is sequestered from the solution phase onto the iron-manganese oxides. When the iron-manganese ratio increases to 4:1, its organic carbon sequestration is close to that of Fe / Mn=5:1, which is 211 mg C / g. When the iron-manganese oxides prepared in Comparative Examples 1-5 were used to test the soil organic carbon sequestration performance, the organic carbon concentration in the solution phase after the reaction was between 35.2 and 40.7 mg C / L, while the organic carbon concentration in the solid phase was between 93 and 148 mg C / g. This indicates that the iron-manganese oxides prepared in Comparative Examples 1-5 performed worse in terms of soil organic carbon sequestration than those prepared in Examples 1-5.

[0156] Experimental Example 3

[0157] (1) Preparation of iron-manganese oxides that retain dissolved organic carbon

[0158] Take ten 1000 mL wide-mouth bottles, numbered 1-10, and add 500 mL of 50 mg C / L soil DOM solution to each. Then add 1 g of the iron-manganese oxide prepared in Examples 1-5 and Comparative Examples 1-5 to each bottle, and shake thoroughly to obtain a suspension. Adjust the pH of the suspension to 7.0 ± 0.2 with 0.1 mol / L HCl or 0.1 mol / L NaOH, tighten the caps, and place all the wide-mouth bottles in a shaker. Shake at 200 rpm for 24 h to allow the reaction to proceed completely.

[0159] After the reaction, the suspension was transferred to centrifuge tubes and centrifuged at 5000 rpm for 30 min. The supernatant was discarded, and the solid at the bottom of the centrifuge tubes was washed several times with pure water and allowed to air dry. The solid was collected to obtain a composite precipitate, which was used to further verify the release of organic carbon immobilized by iron and manganese oxides in soil solutions with different pH values.

[0160] (2) Stability test of fixed organic carbon:

[0161] Three types of soil were selected from Changsha City, Hunan Province; Shaoguan City, Guangdong Province; and Daye City, Hubei Province, with pH values ​​of 4.9, 6.7, and 8.3, respectively. The stability of organic carbon fixed by iron-manganese oxides was tested using the extracts from these three soils. 80 g of each of the three soil types was weighed into a 1000 mL wide-mouth bottle, 800 mL of pure water was added, and the mixture was extracted by shaking at 200 rpm for 2 h. After standing for 30 min, 600 mL of the supernatant was collected as the soil extract.

[0162] Transfer 50 mL of soil extract into a 100 mL wide-mouth bottle. Add 0.2 g of the air-dried composite precipitate to each treatment group, while no composite precipitate was added to the control group. On day 7, measure the organic carbon content in the solution. The difference in organic carbon content between the treatment and control groups represents the amount of organic carbon released from iron-manganese oxide-bound solutions. See the results below. Figure 12 .

[0163] Conclusion: From Figure 12 It can be seen that when the stability of immobilized organic carbon was tested using the iron-manganese oxides prepared in Examples 1-5, the organic carbon remained stable for a long time in the composite precipitation of iron-manganese oxides in three different soil extracts. In the slightly acidic soil solution of Changsha City, Hunan Province, after 7 days of incubation, 98%-99% of the organic carbon was immobilized in the prepared iron-manganese oxides, with only 1%-2% of the organic carbon released into the solution phase. In the slightly neutral soil solution of Shaoguan City, Guangdong Province, after 7 days of incubation, 98%-99% of the organic carbon was also immobilized in the iron-manganese oxides, with only 1%-2% of the organic carbon released into the solution phase. In the slightly alkaline soil solution of Shantou City, Guangdong Province, after 7 days of incubation, 97%-99% of the organic carbon was immobilized in the iron-manganese oxides, with only 1%-3% of the organic carbon released into the solution phase. These results indicate that active organic carbon can be stably immobilized by nano-iron-manganese oxides in soil solutions with pH values ​​ranging from 4.9 to 8.3 for a long period of time. When the iron-manganese oxides prepared in Comparative Examples 1-5 were used to test the stability of fixed organic carbon, 5%-9% of the organic carbon was released in the composite precipitate of iron-manganese oxides in three different soil extracts. This result indicates that the iron-manganese oxides prepared in Comparative Examples 1-5 performed worse in terms of fixing the stability of soil organic carbon than those prepared in Examples 1-5.

[0164] Experiment Example 4

[0165] (1) Extraction of organic matter solidified by iron and manganese oxides

[0166] Take five 1000 mL wide-mouth bottles, numbered 1-5, and add 500 mL of 50 mg C / L soil DOM solution to each. Then add 0.2 g of the iron-manganese oxide prepared in Examples 1-5 to each bottle, and shake thoroughly to obtain a suspension. Adjust the pH of the suspension to 7.0 ± 0.2 with 0.1 mol / L HCl or 0.1 mol / L NaOH, tighten the caps, and place all the wide-mouth bottles in a shaker. Shake at 200 rpm for 24 h to allow the reaction to proceed completely.

[0167] After the reaction, the suspension was transferred to a centrifuge tube and centrifuged at 5000 rpm for 30 min. The supernatant was discarded, and the same volume of 0.1 mol / L NaOH solution was added to extract the organic matter solidified by the iron and manganese oxides. After thorough mixing, the mixture was centrifuged again and the supernatant was collected. The mixture was then filtered through a 0.45 µm filter membrane to obtain the filtrate.

[0168] (2) Molecular characterization of organic matter preserved by iron-manganese oxides

[0169] The collected filtrate was adjusted to pH 2.0 with 1 mol / L HCl, followed by solid-phase extraction using a PPL column. The eluent was obtained by methanol elution and characterized by high-resolution mass spectrometry using a Fourier transform ion cyclotron resonance mass spectrometer (Bruker Daltonik GmbH, Bremen, Germany). The results are shown in [reference needed]. Figures 13-14 .

[0170] Conclusion: From Figure 13 and Figure 14 It can be seen that as the iron-manganese molar ratio increases, the organic matter immobilized on iron-manganese oxides shifts towards lower molecular weights. The proportion of high molecular weight organic matter (600-800 Da) decreases from 49.1% in Fe / Mn=1:1 to 36.0% in Fe / Mn=5:1, indicating that manganese content plays an important role in the oxidative polymerization of organic matter. When the iron-manganese molar ratio is 4:1, the proportion of high molecular weight organic matter (600-800 Da) immobilized on iron-manganese oxides is relatively high, reaching 42.9%. High molecular weight organic matter usually has a more complex and inert structure, such as aromatic ring structure, which can better protect the organic matter from microbial degradation. Therefore, considering both the immobilization and oxidative polymerization effects of iron-manganese oxides, the iron-manganese oxide with Fe / Mn=4:1 has the strongest carbon fixation effect.

[0171] Application examples:

[0172] The iron-manganese oxide materials prepared in Examples 1-5 of this invention can be used as soil sinkers and applied in the following scenarios:

[0173] Farmland soil carbon sequestration: Applied to farmland soils to enhance their carbon sequestration capacity. During crop fallow periods, the iron-manganese oxide material prepared in Example 4 is evenly spread on the soil surface at a rate of 50-100 kg per acre, and then incorporated into the 0-20 cm tillage layer through tillage. This effectively fixes DOM (domestic organic carbon) produced from rhizosphere deposits and organic matter decomposition, converting it into more stable mineral-bound organic carbon. In addition to carbon sequestration, it can also fix heavy metals, thereby improving the safety of agricultural products.

[0174] Degraded soil remediation: Used to restore organic carbon-poor soils such as those from desertification and mining reclamation, and to improve soil structure. The iron-manganese oxide material prepared in Example 4 is evenly spread on the soil surface at a rate of 100-200 kg per acre, and then incorporated into the top 0-20 cm of soil through tilling. This material not only increases carbon sequestration, but the iron and manganese trace elements it provides also improve the soil microbial community structure and promote ecosystem restoration.

[0175] Soil carbon pool protection: Applied to organic-rich soils such as peatlands and forests, this method enhances the soil carbon pool's resistance to climate change. The iron-manganese oxide material prepared in Example 4 is evenly spread on the soil surface at a rate of 50-100 kg per acre, and then incorporated into the top 0-20 cm of soil through tilling. This material can combine with soil organic matter to form a more stable organic-mineral complex, reducing the temperature sensitivity of organic matter decomposition and more stably sequestering organic carbon in the soil.

[0176] Although the principles of the present invention have been described in detail above with reference to preferred embodiments, those skilled in the art should understand that the above embodiments are merely illustrative explanations of the implementation of the present invention and are not intended to limit the scope of the present invention. The details in the embodiments do not constitute a limitation on the scope of the present invention. Any obvious changes, such as equivalent transformations or simple substitutions, based on the technical solutions of the present invention without departing from the spirit and scope of the present invention fall within the protection scope of the present invention.

Claims

1. A method for producing an iron-manganese oxide having a carbon fixation ability, characterized by, The method comprises the following steps: dissolving a soluble ferric salt and a soluble manganese salt in water to obtain a mixed salt solution, adding a basic precipitant to the mixed salt solution to adjust the pH, and stirring to react, after the reaction is completed, obtaining a precipitate suspension, aging and oxidizing the suspension, after the reaction is completed, centrifuging, washing, freeze-drying, grinding and sieving the obtained precipitate to obtain an iron-manganese oxide with carbon sequestration capacity; The aging and oxidizing is performed at a temperature of 30-40℃ for 45-50 hours.

2. The method of producing iron-manganese oxides having a carbon fixation ability according to claim 1, characterized by, In the mixed salt solution, the molar ratio of Fe 3+ and Mn 2+ is 1-5:1; and / or, The soluble ferric salt is selected from one or more of ferric chloride hexahydrate, ferric nitrate nonahydrate, and ferric sulfate pentahydrate; and / or, The soluble manganese salt is selected from one or more of manganese chloride tetrahydrate, manganese nitrate tetrahydrate, and manganese sulfate tetrahydrate.

3. The method of producing iron-manganese oxides having a carbon fixation ability according to claim 1, characterized by, In the mixed salt solution, the molar ratio of Fe 3+ and Mn 2+ is 4:1; and / or, The soluble ferric salt is selected from ferric chloride hexahydrate; and / or, The soluble manganese salt is selected from manganese chloride tetrahydrate.

4. The method of producing iron-manganese oxides having a carbon fixation ability according to claim 1, characterized by, The rate of adding the basic precipitant to the mixed salt solution is 2 mL / min; and / or, The basic precipitant is one or a mixture of sodium hydroxide solution and potassium hydroxide solution; and / or, The concentration of the basic precipitant is 1-5 mol / L.

5. The method of producing iron-manganese oxides having a carbon fixation ability according to claim 1, characterized by, The pH is 8-10; and / or, The stirring time is 2-4 hours.

6. The method of producing iron-manganese oxides having a carbon fixation ability according to claim 1, characterized by, The centrifuging is performed at a speed of 4500-5500 rpm; and / or, The freeze-drying is performed at a temperature of -45℃; and / or, The sieving is performed with a mesh size of 200 mesh.

7. An iron-manganese oxide having a carbon fixation ability, characterized by, The iron-manganese oxide is prepared by the method of any one of claims 1-6.

8. The iron-manganese oxide having a carbon fixation ability according to claim 7, characterized by, The iron-manganese oxide has a weak crystalline state; and / or, The specific surface area of the iron-manganese oxide is 190-290 m 2 / g.

9. Use of the iron-manganese oxide with carbon sequestration capacity of claim 7 as a soil sink enhancer in carbon sequestration in farmland soil, degraded soil remediation, and soil carbon pool protection.

10. Use according to claim 9, characterized in that, The pH of the soil is 4.9-8.3.

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