Magnetic charcoal-based saline-alkali soil conditioner as well as preparation method and application thereof

Abstract

The invention discloses a magnetic biochar-based saline-alkali soil conditioner as well as a preparation method and application thereof, after a biochar material is loaded on ferrous iron, the biochar material is subjected to alkaline oxidation to obtain ferroferric oxide and a porous biochar material in a stable state, and finally activated humic acid, betaine, trehalose and melatonin are combined with magnetic biochar. The magnetic charcoal-based saline-alkali soil conditioner is low in price and easy to obtain and has a good improvement effect on physicochemical properties of saline-alkali soil and promotion of rice growth, and the preparation process is simple and easy to operate.

Description

Technical Field

[0001] The present invention belongs to the technical field of saline-alkali soil conditioner and its manufacturing method. Specifically, the present invention relates to a magnetic biochar-based saline-alkali soil conditioner and its preparation method and application. Background Art

[0002] Saline-alkali soil is a type of soil that has been degraded due to salt pollution. It is widely distributed around the world, covering an area of ​​about 954.83 million hectares. Saline-alkali soil is usually accompanied by problems such as lack of humus fertilizer sources and low cation exchange capacity, which causes soil aggregates to become compacted, air permeability and water permeability are poor, and nutrients are lost and deficient, which in turn reduces crop yield and quality. Extreme climate, special terrain and human activities are the main causes of the formation of saline-alkali land. Among them, coastal saline-alkali land is usually formed due to high groundwater levels, which are accompanied by the rise and evaporation of water, carrying a large amount of soluble salts to the soil surface. The high salt content of saline-alkali soil causes serious degradation of soil structure and physical and chemical properties, which is toxic to plants, resulting in reduced crop yields or even death, which seriously restricts the agricultural development of saline-alkali land.

[0003] Half of the world's population relies on rice as their staple food, accounting for 23% of all food calories consumed worldwide. China is the world's largest rice producer and consumer. In 2020, rice planting area accounted for 25.8% of the total area of ​​grain crops, and rice production accounted for 32% of total grain production. Due to climate reasons and human conditions, the available arable land and land area in my country are decreasing year by year. Therefore, improving saline-alkali soil as rice arable land to achieve "suitable planting" is an important means to ensure my country's food security and is of great significance to the development of saline-alkali land agriculture.

[0004] Biochar (BC) is a porous material generated by the degradation of biomass such as straw under high temperature, anaerobic or low oxygen environment. It not only has the advantages of large specific surface area (SSA), stable structure, wide source of raw materials and low cost, but also helps to realize the resource utilization of straw and carbon sequestration and emission reduction by returning it to the field. Biochar is used as a soil conditioner in saline-alkali soil improvement, which has attracted widespread attention because it can improve soil water holding capacity, organic carbon (OC) content, cation exchange capacity (CEC), nutrients (such as N, P, K), enzyme activity and improve soil aggregates and microbial community structure, thereby reducing the toxic effects of saline-alkali soil on crops. Biochar can effectively promote the growth of crops in saline-alkali land, thereby increasing crop yields and has great application potential. However, there are also reports that direct application of biochar may have poor or even negative effects on saline-alkali land improvement. Because the soluble alkali ions (Na + , K + , Ca 2+ Mg 2+) and minerals will increase soil salinity, and excessive application of biochar may lead to further degradation of saline-alkali soil and inhibit crop growth. Therefore, it is urgent to develop a biochar composite material that can adapt to saline-alkali soil improvement.

[0005] Iron modification of biochar can not only make biochar have a larger specific surface area and pore size, but also obtain more surface oxygen-containing functional groups (hydroxyl, carboxyl, etc.), which is more conducive to the adsorption of humic acid, betaine, trehalose, and melatonin by biochar. Iron is an indispensable trace element for plant growth. It plays a key role in crop growth and development by participating in chlorophyll synthesis, redox reactions, and as a component of various enzymes. Therefore, the application of humic acid iron modified biochar in saline-alkali land can not only increase external nutrients and improve soil physical and chemical properties, but also increase soil porosity, improve salt solution leaching, and improve crop resistance. Summary of the invention

[0006] The purpose of the present invention is to provide a magnetic biochar-based saline-alkali soil conditioner and its preparation method and application, so as to solve the problems described in the above background and achieve beneficial effects. The novel biochar-based soil conditioner of the present invention, through special cracking, oxidation and other steps, loads ferrous iron on biochar material, and then alkaline-oxidizes it to obtain ferroferric oxide and porous biochar material in a stable state, so that nano-magnetic iron and humic acid and other components can be effectively and evenly loaded on biochar, and the obtained biochar composite material has a strong potential for saline-alkali land restoration. The humic acid magnetic biochar (HA-Fe 3 O 4 @BC), with low cost, good effect and simple preparation process, has a good prospect for application in saline-alkali land improvement.

[0007] In order to solve the above-mentioned technical problems, the present invention is implemented by the following technical solutions:

[0008] A method for preparing a magnetic biochar-based saline-alkali soil conditioner comprises the following steps:

[0009] (1) mixing biomass, trivalent iron salt and thiourea in a certain proportion and then firing to obtain ferrous biochar;

[0010] (2) Oxidizing the ferrous biochar under appropriate alkaline conditions and temperature conditions to obtain magnetic biochar.

[0011] The ferric iron salt in step (1) comprises at least one of ferric chloride, ferric sulfate and ferric nitrate; the biomass comprises at least one of rice straw, cotton straw, tobacco straw and reed straw; the biomass is crushed and passed through a 60-100 mesh sieve. Preferably, the particle size of the rice straw is 0.2-1 mm.

[0012] In step (1), the raw material ratio of biomass, trivalent iron salt and thiourea is 3-5:8-10:1-3, and the mixed firing temperature is 300-500° C. and the time is 60-120 min.

[0013] The preparation method is preferably that in step (1), the biomass, trivalent iron salt and thiourea are dissolved in 100-150 ml ultrapure water (raw material to pure water solid-liquid ratio 12-18 g / 100-150 ml) at a raw material ratio of 3-5:8-10:1-3, stirred and mixed, and the mixture is stirred at 70-80°C for at least 12 hours to evaporate to dryness, and then placed in an oven at 70-80°C to evaporate the solution to dryness to obtain a precursor. The precursor is placed in a muffle furnace at a heating rate of 10-15°C / min and heated to 400-500°C for calcination for 100-120 minutes to obtain ferrous biochar.

[0014] The alkaline conditions of step (2) are pH 8-12, temperature 60-90° C., and time 12-24 h.

[0015] In step (2), the pH is adjusted by using at least one of sodium hydroxide, potassium hydroxide and sodium carbonate, and preferably the concentration of at least one of sodium hydroxide, potassium hydroxide and sodium carbonate is 0.8 to 1.0 mol / L.

[0016] The preparation method is preferably that in step (2), 8 to 10 parts of ferrous chloride biochar are added to 100 to 150 parts of ultrapure water by weight, and then sodium hydroxide solution is added to adjust the pH to 9 to 10, and mixed and stirred at 100 to 120 rpm and 70 to 90° C. for 20 to 24 hours. The biochar is then filtered with clean water and then placed in an oven at 70 to 80° C. to evaporate the solution to dryness, thereby obtaining magnetic biochar.

[0017] Furthermore, the magnetic biochar is combined with activated humic acid, trehalose, betaine and melatonin to obtain a humic acid magnetic biochar-based saline-alkali soil conditioner.

[0018] Specifically, humic acid, betaine, trehalose and melatonin are dissolved and activated in an alkaline solution, and then the magnetic biochar is fully combined with them. The mixture is then adjusted to neutral, and finally filtered and cleaned to reduce the salt content in the biochar.

[0019] Furthermore,

[0020] Magnetic biochar, humic acid, trehalose, betaine and melatonin are weighed in a mass ratio of 20-24:4-6:2-3:1-2:0.5-1, and 100-120 ml of 1-1.5 mol / L sodium hydroxide solution is added to the mixture of humic acid, trehalose, betaine and melatonin, with a solid-liquid ratio of 7.5-12 g / 100-120 ml to the solution. The mixture is dissolved and activated at room temperature, and after being fully dissolved and stirred, the magnetic biochar is added and stirred for 40-48 hours. After stirring, the pH value of the solution is adjusted to 6-8 with at least one of hydrochloric acid, sulfuric acid and nitric acid, and the mixture is allowed to stand at room temperature for at least 24 hours. Finally, the mixture is washed and filtered with water, and then dried to obtain a humic acid magnetic biochar saline-alkali soil conditioner.

[0021] The preparation method is preferred, in which the magnetic iron biochar, humic acid, betaine, trehalose and melatonin are weighed in a mass ratio of 20-24:4-6:2-3:1-2:0.5-1 respectively in step (3), 100-120 ml of 1-1.5 mol / L sodium hydroxide solution is added to the mixture of humic acid, betaine, trehalose and melatonin, and the mixture is dissolved and activated at room temperature with a magnetic stirrer at 100-120 rpm. After sufficient dissolution and stirring, the magnetic iron biochar is added and stirring is continued for 40-48 hours; after stirring, the pH value of the solution is adjusted to neutral with HCl, and the mixture is allowed to stand at room temperature for 24 hours; finally, the mixture is washed and filtered, and then placed in an oven at 50-60° C. to evaporate the solution to dryness, thereby obtaining a humic acid magnetic biochar saline-alkali soil conditioner.

[0022] The present invention also provides a magnetic biochar-based saline-alkali soil conditioner prepared by the above method.

[0023] The present invention also provides the use of the magnetic biochar-based saline-alkali soil conditioner in improving saline-alkali soil and planting crops.

[0024] The present invention has the following beneficial effects:

[0025] (1) The magnetic biochar-based saline-alkali soil conditioner designed by the present invention is obtained by iron-modifying the biochar material and combining it with activated humic acid, betaine, trehalose, and melatonin to obtain a soil conditioner that has a good effect on saline-alkali soil and promotes rice growth.

[0026] (2) The magnetic biochar-based saline-alkali soil conditioner designed by the present invention reduces the toxic effects of saline-alkali soil on rice by increasing the soil organic carbon (OC) content, cation exchange capacity (CEC), nutrients (such as N, P, K) and improving soil aggregates and microbial community structure.

[0027] (3) The magnetic biochar-based saline-alkali soil conditioner designed by the present invention contains biochar materials that can prevent iron elements from agglomerating and provide necessary trace elements for rice growth.

[0028] (4) The magnetic biochar-based saline-alkali soil conditioner designed by the present invention is cheap, easily available, highly effective in improving soil, and has a simple preparation process. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a schematic diagram of the structure of the straw magnetic biochar-based saline-alkali land improver prepared by the present invention;

[0030] Among them, 1-biochar, 2-Fe 3 O 4 , 3-humic acid, betaine, trehalose, and melatonin combined with biochar.

[0031] Figure 2 It is a flow chart of the preparation process of the present invention.

[0032] Figure 3 SEM images of BC (a), F2 (b), F3 (c) and HAF (d), and SEM-EDS spectra of c, Fe, O, S and Cl elements.

[0033] Figure 4 X-ray diffraction patterns of BC, F2, F3 and HAF.

[0034] Figure 5 High-resolution Fe2p XPS spectra of F2, F3 and HAF.

[0035] Figure 6 This is a diagram showing the effect of each treatment group of the present invention on promoting rice growth;

[0036] Among them, a-rice germination rate, b-rice plant height, c-rice morphology. DETAILED DESCRIPTION

[0037] Now, the preparation method and application of a biochar-based saline-alkali land soil conditioner of the present invention are further explained in combination with the embodiments and the accompanying drawings. Obviously, this implementation case is only used as a further explanation of the preparation method of the straw biochar-based saline-alkali land conditioner designed by the present invention, so that those skilled in the art can more fully understand the technical means adopted by the present invention, and does not constitute any form of limitation on the technical design of the present invention. Any invention or invention made based on the design principle of the present invention without creative labor should be protected by the present invention.

[0038] The invention provides a preparation method of a straw biochar-based saline-alkali soil conditioner and raw materials required for its application: rice straw, ferric chloride hexahydrate, thiourea, humic acid, sodium hydroxide, hydrochloric acid, betaine, trehalose and melatonin.

[0039] Example 1

[0040] The following steps are involved:

[0041] The first step is to pre-treat the material: the rice straw is preliminarily crushed, the flaked straw is dried at 75°C, and the dried raw material is crushed and sieved (60 meshes) into straw powder for later use.

[0042] The second step is the preparation of raw biochar: weigh 10g of rice straw powder into a crucible and place it in a muffle furnace for pyrolysis reaction. The heating rate is 10℃ / min, the pyrolysis temperature is 400℃, the duration is 2h, the atmosphere is nitrogen, and the nitrogen flow rate is 120ml / min to obtain raw biochar.

[0043] Example 2

[0044] 10g of ferric chloride was dissolved in a beaker containing 100ml of ultrapure water, and then 2g of thiourea was added for dissolution, and then 4g of rice powder was added and stirred at 75°C and 100rpm for 10h, and finally placed in an oven at 75°C to evaporate the solution to dryness, thereby obtaining a precursor material. The precursor material was fired under the same conditions as in Example 1 to obtain ferrous chloride biochar.

[0045] Example 3

[0046] 10 g of ferrous chloride biochar prepared in Example 2 was added to 150 ml of ultrapure water, and then 1 mol / L sodium hydroxide solution was added to adjust the pH to 10, and mixed and stirred at 100 rpm and 75° C. for 24 h. The biochar was then washed with ultrapure water and filtered to a pH of 7, and then placed in an oven at 75° C. to evaporate the solution to dryness, thereby obtaining magnetic biochar.

[0047] Example 4

[0048] 4 g humic acid, 2 g betaine, 1 g trehalose and 0.5 g melatonin were weighed and dissolved in 100 ml 1 mol / L sodium hydroxide solution, and dissolved and activated at room temperature with a magnetic stirrer at 100 rpm. After fully dissolved and stirred, 24 g magnetic biochar was added and continued to stir for 48 h. After stirring, the pH of the solution was adjusted to 7 with HCl, and the mixture was allowed to stand at room temperature for 24 h. Finally, the mixture was washed and filtered with water, and then placed in an oven at 60 ° C to evaporate the solution to dryness to obtain a humic acid magnetic biochar saline-alkali soil conditioner.

[0049] For convenience, the original biochar was named BC, the ferrous chloride biochar was named F2, the magnetic biochar was named F3, the humic acid magnetic biochar was named HAF, and the mixture of humic acid, betaine, trehalose, and melatonin was named HA.

[0050] Four biochar-based saline-alkali land conditioners were prepared according to the methods described in Examples 1-4, and material characterization of these four soil conditioners was performed.

[0051] In the first step, the microstructure and surface element distribution of BC, F2, F3 and HAF materials were observed using a scanning electron microscope and an energy spectrometer. Figure 3 a shows that the geometry of BC is irregular, mainly composed of micron-sized tissues, without obvious pore structures, and retains the physical form of the original rice straw biomass. Compared with the modified F3 and HAF biochar materials, the size is larger, and its elemental composition is mainly C and O elements, with very small amounts of Cl, Fe and S. This is because the biochar itself contains these elements. After the pyrolysis experiment, after loading iron crystals, Figure 3 The F2 material in b has a micron-level porous material structure. EDS further shows the elemental composition of F2, and it can be found that there are obvious Fe, O, C, and Cl elements, and Fe and Cl elements are mainly distributed in the bulk material, further proving that this bulk material is FeCl 2 , while C and O come from the biochar carrier. F3 ( Figure 3 c) Obvious spherical particles appear on the surface. The spherical particles are arranged in a disordered manner and have different diameters. The larger particles may be Fe 3 O 4 Agglomeration is formed. In addition, after oxidation, the particle size of F3 material drops to submicron level (100nm-1μm), so the specific surface area of ​​F3 is significantly improved. Further observation of the energy spectrum shows that compared with F2, the Cl content on the surface of F3 is significantly reduced, and the O content is increased, which is caused by oxidation reaction and cleaning. Figure 3 As for the HAF of d, the irregular spherical granular substances in the F3 material disappeared obviously, which should be caused by the introduction of humic acid, betaine, trehalose and melatonin covering the surface.

[0052] The second step is, Figure 4 As shown in Figure 1, the XRD detection of the original biochar (BC) obtained by pyrolysis of pure biomass shows that there are clear characteristic peaks at 2θ = 28.46°, 40.59°, 50.22°, 58.69°, 66.45° and 73.59°, which belong to KCl (PDF#75-0296), indicating that BC contains a high amount of KCl, which is due to the nature of biomass straw itself. On the other hand, by mixing thiourea and FeCl 3 6H2 O reacts at high temperature to make FeCl 3 Reduction to obtain FeCl 2 , and by adding FeCl 2 Oxidation under alkaline conditions can produce Fe 3 O 4 The rice straw powder, thiourea and ferric chloride were mixed and calcined at high temperature to obtain the intermediate material FeCl2 for loading iron onto biochar. 2 @BC.FeCl 2 The XRD detection of @BC shows that there are clear characteristic peaks at 2θ=16.11°, 20.82°, 32.52° and 37.59., which belong to FeCl 2 (PDF#25-1040), demonstrating the formation of this pure intermediate. 2 @BC was oxidized under alkaline conditions to obtain Fe 3 O 4 @BC. Then, Fe 3 O 4 @BC is used to adsorb the activated mixture of humic acid, betaine, trehalose and melatonin to obtain HA-Fe 3 O 4 @BC. For Fe 3 O 4 @BC and HA-Fe 3 O 4 @BC sample, XRD detection shows that there are five characteristic peaks at 2θ=30.7, 35.6, 43.4, 57.5, 62.5°, which belong to Fe 3 O 4 (PDF#89-3854), basically with Fe 3 O 4 These results show that Fe is indeed formed in the composite material F3 and HAF. 3 O 4 Crystal.

[0053] 3FeCl 2 +4NaOH+O 2 =Fe 3 O 4 +4NaCl+2H 2 O+2Cl - (1)

[0054] The third step is Figure 5As shown in the figure, the material was characterized by XPS spectrum detection, and the elemental composition of the surface of F2, F3, and HAF materials was observed. The two sub-bands formed at 711~eV and 713~eV on the 3 / 2 orbital of Fe2p in the high-resolution Fe2p XPS spectrum represent Fe 2+ and Fe 3+ , the two subbands formed at 724~eV and 725~eV on the 1 / 2 orbital of Fe2p represent Fe 2+ and Fe 3+ The two asymmetric peaks at 718~eV and 735~eV are satellite peaks, so there are Fe 2+ and Fe 3+ For materials F2 and F3, Fe 3+ The relative content has been significantly increased. 2+ Oxidized to Fe 3+ , FeCl 2 Oxidized to form Fe 3 O 4 This is consistent with the detection results in the XRD spectrum, further proving that FeCl 2 To Fe 3 O 4 The conversion of HAF relative to Fe in F3 3+ The decrease in relative content is due to the reducing properties of humic acid and melatonin.

[0055] Four biochar-based saline-alkali land conditioners were prepared according to the methods described in Examples 1-4, and the performance of these four soil conditioners and pure humic acid was evaluated.

[0056] In the first step, 200 g of fresh soil sample was placed in a plastic box (3 cm in height, 10 cm in length and width) and mixed evenly with biochar. 3% w / w BC, F2, F3, HAF and HA (0.43%) were evenly mixed in the soil at the application amount for use, where the HA application amount was consistent with the loading amount.

[0057] The second step is to disinfect the rice seeds (Qingliangyou 326) with 5% sodium hypochlorite and soak them in clean water for 24 hours. Then, wrap the seeds with a wet towel and place them in a constant temperature box at 38°C for 24 hours of germination. Sow the germinated rice seeds in the soil with different treatments, 100 seeds per box. Cultivate in a constant temperature room at 24-28°C. After the rice grows to two leaves and one heart (about 20 days), add 0.8g NaCl into the box and continue to cultivate for 15 days under 0.4% salt conditions.

[0058] The third step is to wash the collected rice plants with distilled water after cultivation, separate them into the above-ground and underground parts, and measure the plant height, root length, and stem thickness. The experiment was repeated three times and the data were averaged. Figure 5 As shown in Table 1. HAF has the best effect on promoting rice growth in terms of germination rate, total root length, longest root length, stem diameter and dry matter content, and has the best improvement effect in reducing soil electrical conductivity (EC) and increasing soil total nitrogen (TN) content.

[0059] Table 1 Agronomic characteristics of rice and soil EC

[0060]

[0061]

[0062] Note: Values ​​with the same letters in the same column are not significantly different (p>0.05).

[0063] The above implementation cases describe the basic raw materials and main features of the present invention and the advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above implementation cases. The above implementation cases and the description only illustrate the specific working principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which all fall within the scope of the present invention. The scope of protection required by the present invention is defined by the attached claims and their equivalents.

Claims

1. A method for preparing a magnetic biochar-based saline-alkali soil conditioner, characterized in that: The following steps are involved: (1) mixing biomass, trivalent iron salt and thiourea in a certain proportion and then firing to obtain ferrous biochar; (2) Oxidizing the ferrous biochar under appropriate alkaline conditions and temperature conditions to obtain magnetic biochar.

2. The method for preparing the magnetic biochar-based saline-alkali soil conditioner according to claim 1, characterized in that: The ferric iron salt described in step (1) comprises: at least one of ferric chloride, ferric sulfate, and ferric nitrate; the biomass comprises at least one of rice straw, cotton straw, tobacco straw, and reed straw; and the biomass is crushed and passed through a 60-100 mesh sieve.

3. The method for preparing the magnetic biochar-based saline-alkali soil conditioner according to claim 1 or 2, characterized in that: In step (1), the raw material ratio of biomass, trivalent iron salt and thiourea is 3-5:8-10:1-3, and the mixed firing temperature is 300-500° C. and the time is 60-120 min.

4. The method for preparing the magnetic biochar-based saline-alkali soil conditioner according to claim 1, characterized in that: The alkaline conditions of step (2) are pH 8-12, temperature 60-90° C., and time 12-24 h.

5. The method for preparing the magnetic biochar-based saline-alkali soil conditioner according to claim 1 or 4, characterized in that: In step (2), the pH is adjusted by using at least one of sodium hydroxide, potassium hydroxide and sodium carbonate, and preferably the concentration of at least one of sodium hydroxide, potassium hydroxide and sodium carbonate is 0.8 to 1.0 mol / L.

6. The method for preparing the magnetic biochar-based saline-alkali soil conditioner according to any one of claims 1 to 5, characterized in that: The magnetic biochar is combined with activated humic acid, trehalose, betaine and melatonin to obtain a humic acid magnetic biochar-based saline-alkali soil conditioner.

7. The method for preparing the magnetic biochar-based saline-alkali soil conditioner according to claim 6, characterized in that: The process is to dissolve and activate humic acid, betaine, trehalose and melatonin in an alkaline solution, allow the magnetic biochar to fully combine with the solution, adjust the mixture to neutrality, and finally filter and wash it to reduce the salt content in the biochar.

8. The method for preparing the magnetic biochar-based saline-alkali soil conditioner according to claim 7, characterized in that: Magnetic biochar, humic acid, trehalose, betaine and melatonin are weighed in a mass ratio of 20-24:4-6:2-3:1-2:0.5-1, and 100-120 ml of 1-1.5 mol / L alkaline solution is added to the mixture of humic acid, trehalose, betaine and melatonin, with a solid-liquid ratio of 7.5-12 g / 100-120 ml to the solution. The mixture is dissolved and activated at room temperature, and after being fully dissolved and stirred, the magnetic biochar is added and stirred for 40-48 hours. After stirring, the pH value of the solution is adjusted to 6-8 with at least one of hydrochloric acid, sulfuric acid and nitric acid, and the mixture is allowed to stand at room temperature for at least 24 hours. Finally, the mixture is washed and filtered with water, and then dried to obtain a humic acid magnetic biochar saline-alkali soil conditioner.

9. A magnetic biochar-based saline-alkali soil conditioner prepared by the method according to any one of claims 1 to 8.

10. Use of the magnetic biochar-based saline-alkali soil conditioner according to claim 9 in improving saline-alkali soil and planting crops.

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