A biochar-iron composite material, a preparation method and application thereof

Abstract

The present application relates to the technical field of soil improvement, and discloses a biochar-iron composite material, a preparation method and application thereof.The biochar-iron composite material comprises the following raw materials: iron oxide and mangrove plant biochar.The biochar-iron composite material provided by the present application uses mangrove plant biochar with a large specific surface area and porosity as a raw material, which is conducive to promoting the surface complexation of the biochar-iron composite material and soil organic matter and increasing the adsorption amount of soil organic carbon; the iron oxide is used as a raw material, and iron can be combined with organic carbon through adsorption, coprecipitation or complexation to form a complex with high chemical stability, thereby improving the stability of soil organic carbon; meanwhile, the redox process of iron can inhibit the generation of greenhouse gases, reduce carbon emissions, and significantly enhance the soil carbon preservation function; the biochar-iron composite material is suitable for salinized soil with a salinity of 5 ‰-20 ‰, can effectively inhibit the release of soil CO2, and increase the content of stable organic carbon in soil.

Description

Technical Field

[0001] This invention relates to the field of soil improvement technology, and in particular to a biochar-iron composite material, its preparation method, and its application. Background Technology

[0002] The addition of biochar and iron has been shown to effectively improve the soil environment. Biochar, as a porous and highly absorbent material, can adsorb organic matter in the soil and optimize soil structure; while iron can combine with soil carbon to form a stable iron oxide-organic matter complex, which can significantly promote the accumulation of soil organic carbon.

[0003] Mangrove wetlands, as typical "blue carbon" ecosystems, possess extremely high carbon sequestration potential. Organic carbon in wetland soils mainly originates from the input and decomposition of plant residues, microbial activity, and soil physicochemical properties. However, coastal mangrove wetlands have high salinity, which severely impacts primary productivity, inhibits microbial decomposition, and reduces the stability of soil organic carbon. Furthermore, the complex redox conditions in high-salinity environments easily lead to the release of soil carbon. Therefore, there is an urgent need to develop soil amendment materials adaptable to high-salinity environments to promote the accumulation of organic carbon in high-salinity mangrove wetland soils. Summary of the Invention

[0004] The present invention aims to at least solve one of the aforementioned technical problems existing in the prior art. Therefore, one objective of the present invention is to provide a biochar-iron composite material; a second objective is to provide a method for preparing this biochar-iron composite material; and a third objective is to provide applications of this biochar-iron composite material.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A first aspect of the present invention provides a biochar-iron composite material comprising the following raw materials: iron oxide and mangrove biochar.

[0007] In some embodiments of the present invention, the mangrove biochar is prepared by a method comprising the following steps: under anaerobic conditions, pyrolyzing mangrove plant debris and fallen leaves at 300-600°C, followed by acid washing, to obtain the mangrove biochar.

[0008] In some embodiments of the present invention, the pyrolysis temperature is 400-500°C.

[0009] In some embodiments of the present invention, the pyrolysis time is 2-6 hours.

[0010] In some embodiments of the present invention, the particle size of the mangrove biochar is 0.5-2 mm.

[0011] In some embodiments of the present invention, the specific surface area of ​​the mangrove biochar is 150-180 m². 2 / g.

[0012] In some specific embodiments of the present invention, the specific surface area of ​​the mangrove biochar is 155-165 m². 2 / g.

[0013] In some embodiments of the present invention, the porosity of the mangrove biochar is 0.09-0.1 cm. 3 / g.

[0014] In some specific embodiments of the present invention, the porosity of the mangrove biochar is 0.09-0.095 cm. 3 / g.

[0015] In some embodiments of the present invention, the pickling reagent includes hydrochloric acid and sulfuric acid.

[0016] In some embodiments of the present invention, the concentration of the pickling reagent is 1 wt%-5 wt%.

[0017] In some embodiments of the present invention, the pickling process is further divided into washing and drying steps.

[0018] In some embodiments of the present invention, the washing agent includes water.

[0019] In some embodiments of the present invention, the drying temperature is 100-110°C and the time is 20-25 hours.

[0020] In this invention, mangrove biochar is prepared using mangrove plant debris and fallen leaves as raw materials. Mangrove plant debris and fallen leaves are readily available, have high carbon content, and low ash content. Through pyrolysis, mangrove biochar can obtain high porosity and specific surface area. Through acid washing, impurities on the surface of mangrove biochar can be removed, thereby improving the surface activity of the biochar.

[0021] In some embodiments of the present invention, the iron oxide includes hematite.

[0022] In some embodiments of the present invention, the content of ferric oxide in the hematite is greater than 99 wt%.

[0023] In some embodiments of the present invention, the hematite has a particle size of less than 100 mesh.

[0024] In some specific embodiments of the present invention, when the iron oxide is hematite, the method further includes a step of heating the hematite in a water bath at 70-90°C.

[0025] In this invention, hematite is used as the iron source. Hematite is inexpensive and has good ecological compatibility in the natural environment. Heating hematite in a water bath at 70-90℃ can oxidize the ferrous iron in the hematite to generate iron oxides with high chemical stability.

[0026] In some embodiments of the present invention, the mass ratio of the iron oxide to mangrove biochar is 1:(5-15).

[0027] In some specific embodiments of the present invention, the mass ratio of the iron oxide to mangrove biochar is 1:(5-10).

[0028] A second aspect of the present invention provides a method for preparing the biochar-iron composite material described in the first aspect of the present invention, comprising the following steps:

[0029] Iron oxides were mixed with mangrove biochar and calcined at 100-150°C to obtain the biochar-iron composite material.

[0030] In some embodiments of the present invention, the process of mixing the iron oxide with mangrove biochar is aided by stirring.

[0031] In some embodiments of the present invention, the iron oxide is mixed with mangrove biochar for 30-60 minutes.

[0032] In some embodiments of the present invention, the iron oxide is mixed with mangrove biochar and then sprayed with water on the surface.

[0033] In some embodiments of the present invention, the calcination time is 12-24 hours.

[0034] In some specific embodiments of the present invention, the calcination time is 15-20 hours.

[0035] In this invention, iron oxide and mangrove biochar are thoroughly mixed and then calcined at a low temperature of 100-150°C, which can effectively improve the bonding strength between biochar and iron.

[0036] The third aspect of the present invention provides the application of the biochar-iron composite material described in the first aspect of the present invention in the improvement of saline-alkali soil.

[0037] In some embodiments of the present invention, the soil improvement includes enhancing the carbon sequestration performance of saline soils.

[0038] In some embodiments of the present invention, the salinity of the salinized soil is 5‰-20‰.

[0039] In some embodiments of the present invention, the salinized soil includes salinized soil from estuary mangroves and salinized soil from coastal mangroves.

[0040] In some embodiments of the present invention, the amount of the biochar-iron composite material is 10wt%-50wt% of the saline soil.

[0041] In some embodiments of the present invention, the biochar-iron composite material is applied to a depth of 0-20 cm in the surface layer of the saline soil.

[0042] Compared with the prior art, the beneficial effects of the present invention are:

[0043] 1) The biochar-iron composite material provided by this invention uses mangrove biochar, which has a large specific surface area and porosity, as the raw material. This is beneficial to promoting the surface complexation of the biochar-iron composite material with soil organic matter and increasing its adsorption capacity for soil organic carbon. Using iron oxide as the raw material, iron can combine with organic carbon through adsorption, co-precipitation or complexation to form complexes with high chemical stability, thereby improving the stability of soil organic carbon. At the same time, the redox process of iron can also inhibit the generation of greenhouse gases, reduce carbon emissions, and significantly enhance the soil carbon storage function.

[0044] 2) The preparation method of biochar-iron composite material provided by the present invention has simple steps, mild process conditions, and is suitable for industrial application;

[0045] 3) The biochar-iron composite material provided by this invention is suitable for saline soils with a salinity of 5‰-20‰. It can effectively inhibit the release of soil CO2, increase the content of soil stable organic carbon, reduce the loss of soil organic carbon, and improve the carbon fixation performance of saline soil. It can also increase the content of low-crystalline and free iron oxides in the soil, improve the physicochemical properties of high-salt soil, promote the formation of soil aggregates, and improve the soil's resistance to erosion.

[0046] 4) When the biochar-iron composite material provided by this invention is applied to soil improvement, it has a long retention time in the soil and can play a long-term role without the need for multiple additions, thus reducing the workload. A relatively long-lasting organic carbon accumulation effect can be obtained with a single application. Attached Figure Description

[0047] Figure 1 This is a schematic diagram of the preparation process of biochar-iron composite materials in Examples 1-3;

[0048] Figure 2 The results of soil carbon emission tests in the experimental case;

[0049] Figure 3 The results of the soil iron-bound organic carbon content test in the experimental case;

[0050] Figure 4 The results show the total organic carbon content of the soil in the experimental case. Detailed Implementation

[0051] The present invention will be further described in detail below through specific embodiments. Unless otherwise specified, the raw materials, reagents, or apparatus used in the embodiments and comparative examples are all available from conventional commercial sources or can be obtained by existing technical methods. Unless otherwise specified, the test or experimental methods are conventional methods in the art.

[0052] Figure 1 This is a schematic diagram of the preparation process of biochar-iron composite materials in Examples 1-3. Figure 1 As can be seen, the preparation of the biochar-iron composite material in Examples 1-3 includes the steps of pyrolyzing, crushing and sieving, and acid washing of mangrove plant debris to obtain mangrove biochar; crushing and sieving hematite and heating it in a water bath to obtain highly chemically stable iron oxide; and then mixing, stirring, and calcining the mangrove biochar and iron oxide at low temperature to obtain the biochar-iron composite material. The following will refer to... Figure 1 The preparation process of the biochar-iron composite materials in Examples 1-3 is described.

[0053] Example 1

[0054] This embodiment prepares a biochar-iron composite material, and the steps are as follows:

[0055] Mangrove plant debris and fallen leaves were collected and pyrolyzed at 500℃ for 4 hours under anaerobic conditions. The product was collected, ground in a mortar, and sieved through 2mm and 0.5mm sieves to collect particles with a diameter of 0.5-2mm. The particles were then soaked in 2wt% hydrochloric acid for 3 hours to remove surface impurities and improve surface activity. After acid washing, the particles were repeatedly rinsed with distilled water until neutral and dried at 105℃ for 24 hours to obtain mangrove biochar for later use.

[0056] Hematite (ferric oxide content greater than 99wt%) was ground into powder using a mortar and pestle. Particles with a particle size of less than 100 mesh were collected and heated in a water bath at 80℃ to generate iron oxides with high chemical stability for later use.

[0057] Mangrove biochar and iron oxide were uniformly mixed at a mass ratio of 5:1 under stirring conditions. A small amount of distilled water was sprayed on the surface of the mixture, and the mixture was calcined at 105℃ for 18 hours to obtain a biochar-iron composite material.

[0058] Example 2

[0059] This embodiment prepares a biochar-iron composite material, and the steps are as follows:

[0060] Mangrove plant debris and fallen leaves were collected and pyrolyzed at 400℃ for 5 hours under anaerobic conditions. The product was collected, ground in a mortar, and sieved through 2 mm and 0.5 mm sieves to collect particles with a diameter of 0.5-2 mm. The particles were then soaked in 2 wt% hydrochloric acid for 3 hours to remove surface impurities and improve surface activity. After acid washing, the particles were repeatedly rinsed with distilled water until neutral and dried at 100℃ for 25 hours to obtain mangrove biochar for later use.

[0061] Hematite (ferric oxide content greater than 99wt%) was ground into powder using a mortar and pestle. Particles with a particle size of less than 100 mesh were collected and heated in a water bath at 80℃ to generate iron oxides with high chemical stability for later use.

[0062] Mangrove biochar and iron oxide were uniformly mixed at a mass ratio of 8:1 under stirring conditions. A small amount of distilled water was sprayed on the surface of the mixture, and the mixture was calcined at 120℃ for 17 hours to obtain a biochar-iron composite material.

[0063] Example 3

[0064] This embodiment prepares a biochar-iron composite material, and the steps are as follows:

[0065] Mangrove plant debris and fallen leaves were collected and pyrolyzed at 450℃ for 5 hours under anaerobic conditions. The product was collected, ground in a mortar, and sieved through 2 mm and 0.5 mm sieves to collect particles with a diameter of 0.5-2 mm. The particles were then soaked in 2 wt% hydrochloric acid for 3 hours to remove surface impurities and improve surface activity. After acid washing, the particles were repeatedly rinsed with distilled water until neutral and dried at 110℃ for 22 hours to obtain mangrove biochar for later use.

[0066] Hematite (ferric oxide content greater than 99wt%) was ground into powder using a mortar and pestle. Particles with a particle size of less than 100 mesh were collected and heated in a water bath at 80℃ to generate iron oxides with high chemical stability for later use.

[0067] Mangrove biochar and iron oxide were uniformly mixed at a mass ratio of 10:1 under stirring conditions. A small amount of distilled water was sprayed on the surface of the mixture, and the mixture was calcined at 150℃ for 15 hours to obtain a biochar-iron composite material.

[0068] Comparative Example 1

[0069] This comparative example uses rice straw biochar prepared using conventional methods as a comparison.

[0070] Comparative Example 2

[0071] This comparative example uses wood biochar prepared by conventional methods as a comparison.

[0072] Material characterization

[0073] 1. The specific surface area and pore structure parameters of mangrove biochar in Example 1, rice straw biochar in Comparative Example 1, and sawdust biochar in Comparative Example 2 were determined using an automated specific surface area and pore structure analyzer (ASAP 2460):

[0074] Table 1 Comparison of specific surface area and porosity of different biochars

[0075] Comparative Example 1 Rice straw biochar 6.97 0.007 Comparative Example 2 Wood biochar 132.12 0.060 Example 1 Mangrove biochar 158.97 0.091

[0076] Table 1 compares the specific surface area and porosity of different biochars. As shown in Table 1, the mangrove biochar obtained in Example 1, using mangrove plant debris and fallen leaves as raw materials through pyrolysis and acid washing, has a specific surface area of ​​158.97 m². 2 / g, porosity up to 0.091cm 3 Compared with ordinary rice straw biochar and sawdust biochar, mangrove biochar has a significantly increased specific surface area and porosity, which will be more conducive to promoting the surface complexation of biochar-iron composite materials with soil organic matter and increasing its adsorption capacity for soil organic carbon.

[0077] Test case

[0078] Take 12 500mL culture bottles, add 80g of soil with a salinity of 15‰ to each bottle, and pre-culture for 3 days under the conditions of ambient temperature of 25℃ and field water holding capacity of 100% for later use.

[0079] The 12 culture flasks were divided into 4 groups of 3 each; the 3 culture flasks in the first group served as a blank control; 10g of mangrove biochar prepared in Example 1 was added to each of the 3 culture flasks in treatment group 1; 10g of iron oxide prepared in Example 1 was added to each of the 3 culture flasks in treatment group 2; and 10g of biochar-iron composite material prepared in Example 1 was added to each of the 3 culture flasks in treatment group 3. After the addition was completed, the mixture was gently stirred with a glass rod until it was evenly mixed.

[0080] Gases were collected and CO2 concentrations were measured on days 1, 3, 7, 14, 21, 28, 35 and 42 after the addition of different materials; soil samples were collected on day 42 to analyze the content of soil organic carbon, iron-bound organic carbon, iron oxides and soil aggregates.

[0081] The testing methods for each test indicator are as follows:

[0082] 1) CO2 concentration: determined by gas chromatography (GC-2014C, Shimadzu, Japan);

[0083] 2) Total organic carbon content in soil: determined using the potassium dichromate oxidation with external heating method;

[0084] 3) Soil iron-bound organic carbon content: 0.25g dry soil was mixed with 0.25g sodium dithionite and 25mL 0.3mol / L sodium citrate at 80℃ for 15min, centrifuged at 4000rpm for 10min, then washed 3 times with 1mol / L sodium chloride, freeze-dried and ground. Sodium chloride was used as a control experiment to ensure the same ionic strength. After repeating the above steps, the residual organic carbon content after treatment with sodium citrate and sodium chloride was measured. The difference between the organic carbon content after treatment with sodium chloride and sodium citrate is the soil iron-bound organic carbon content.

[0085] 4) Iron oxide content: Add 30 mL of 0.2 mol / L acidic ammonium oxalate to 0.3 g of soil, shake in the dark for 4 h, filter, and determine the content of low-crystalline iron oxides using ICP-OES (iCAP 7000SERIES, China); add 0.5 g of sodium dithionite and 25 mL of 0.3 mol / L sodium citrate to 1 g of soil, shake for 16 h, filter, and determine the content of free iron oxides using ICP-OES (iCAP7000SERIES, China).

[0086] 5) Soil aggregate content: 40g of soil sample was soaked in 1cm deep deionized water for 5 minutes on a 0.25mm sieve. The soil was then sieved for 2 minutes by moving the sieve up and down 50 times to avoid damaging the aggregate structure. Aggregates above the sieve (≥0.25mm) and below the sieve (<0.25mm) were transferred to a pre-weighing container. After sieving and drying, the soil aggregates were separated into large aggregates (≥0.25mm) and micro-aggregates (<0.25mm). The mass of each aggregate size was then accurately weighed, and the percentage of each aggregate size in the total soil sample mass was calculated as the proportion of that aggregate size.

[0087] Table 2 shows the test results of iron oxide content under different treatments in the experimental cases.

[0088]

[0089]

[0090] Where a, b, and c represent significant differences (P < 0.05).

[0091] Table 2 shows the test results of iron oxide content under different treatments in the experimental examples. As can be seen from Table 2, the addition of the biochar-iron composite material prepared in Example 1 to saline soil can significantly increase the content of low-crystalline and free iron oxides in the soil.

[0092] Figure 2 The soil carbon emission test results in the experimental case were obtained by... Figure 2It can be seen that in the treatment group with added biochar-iron composite material prepared in Example 1, the CO2 concentration was consistently lower than that in the blank control group and the biochar (mangrove biochar) and iron oxide treatment group within 1-42 days. Figure 3 The results of the soil iron-bound organic carbon content test in the experimental example are from... Figure 3 It can be seen that, compared with the control group, in the treatment group with added biochar-iron composite material prepared in Example 1, the soil iron-bound organic carbon increased by 70.26% on day 42. Figure 4 The results of the total organic carbon content test in the soil in the experimental case were obtained from... Figure 4 It can be seen that, compared with the control group, the total organic carbon content of the soil increased by 15.14% on day 42 in the treatment group with added biochar-iron composite material prepared in Example 1. This indicates that the biochar-iron composite material provided by the present invention can better inhibit the release of soil CO2 and increase the content of stable organic carbon in the soil. In addition, compared with the control group, the content of soil macroaggregates in treatment group 3 increased by 53.18%. Macroaggregates can sustainably protect organic carbon, reduce the loss of soil organic carbon, and improve the carbon sequestration performance of saline soil.

[0093] Application examples

[0094] Eight 1m × 1m squares were set up in a high-salinity area (salinity 18‰) of a mangrove wetland. Four squares were used as a control group without biochar-iron composite material, while the remaining four squares were each filled with 2kg of the biochar-iron composite material prepared in Example 1. The composite material and soil (0-20cm) were thoroughly mixed with the soil using a small shovel. One month after the addition, gas and soil samples were collected, and indicators such as CO2 concentration and soil organic carbon were measured according to the method described in the experimental example.

[0095] It was found that after treating high-salinity mangrove wetland soil with biochar-iron composite material, soil CO2 emissions decreased by 46.08%, the content of stable organic carbon (iron-bound organic carbon) increased by 62.53%, and the proportion of soil macroaggregates increased by 46.63%. This indicates that the biochar-iron composite material provided by this invention, when practically applied to high-salinity mangrove wetland soil, can effectively inhibit soil CO2 release, increase the content of stable organic carbon in the soil, and the increase in the proportion of macroaggregates improves soil structure, enhances soil erosion resistance, and is more conducive to the sustainable protection of organic carbon.

Claims

1. The application of biochar-iron composite material in improving the carbon sequestration performance of saline soils with a salinity of 5‰-20‰, characterized in that, The biochar-iron composite material is prepared by a method comprising the following steps: mixing iron oxide with mangrove biochar and calcining at 100-150°C to obtain the biochar-iron composite material; wherein... The mangrove biochar is prepared by a method comprising the following steps: under anaerobic conditions, pyrolyzing mangrove plant debris and fallen leaves at 400-500℃, followed by acid washing, to obtain the mangrove biochar; the specific surface area of ​​the mangrove biochar is 150-180 m² / g. 2 / g, porosity is 0.09-0.1cm 3 / g; The iron oxide is hematite; the content of ferric oxide in the hematite is greater than 99 wt%; the hematite is heated in a water bath at 70-90℃ before use.

2. The application according to claim 1, characterized in that, The particle size of the mangrove biochar is 0.5-2 mm.

3. The application according to claim 1, characterized in that, The hematite has a particle size of less than 100 mesh.

4. The application according to claim 1, characterized in that, The mass ratio of the iron oxide to the mangrove biochar is 1:(5-15).

5. The application according to claim 1, characterized in that, The salinized soils include salinized soils from estuary mangrove forests and salinized soils from coastal mangrove forests.

6. The application according to claim 1, characterized in that, The amount of the biochar-iron composite material used is 10wt%-50wt% of the saline soil.

7. The application according to claim 1, characterized in that, The biochar-iron composite material is applied to a depth of 0-20 cm in the surface layer of the saline soil.

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