Calcium-enriched rice straw biochar core-shell particle soil conditioner

Abstract

The invention discloses a calcium-enriched rice straw biochar core-shell particle soil conditioner, which belongs to the technical field of soil improvement and farmland water environment governance, and comprises the following components: a calcium-enriched rice straw biochar core, desulfurized gypsum, a binder and a functional auxiliary agent, the binder is selected from one or more of starch, lignosulfonate, sodium carboxymethyl cellulose and sodium alginate; the functional additive is selected from one or more of humic acid, trace element fertilizer and organic fertilizer; through the comprehensive design on the material structure, the Ca < 2 + > slow release mechanism and the application system, calcium and sodium replacement and soil salinity and alkalinity reduction, flocculation and sedimentation of soil colloid in an alkaline environment, blocking and weakening of a soil-water interface colloid pollution channel and continuous improvement of the soil structure and fertility are synergistically realized.

Description

Technical Field

[0001] This invention belongs to the field of soil improvement and farmland water environment management technology, specifically a calcium-enriched rice straw biochar core-shell granule soil conditioner. Background Technology

[0002] Soda-saline-alkali land is widely distributed in Northeast and Northwest my country. Its soil solution pH is generally between 8.5 and 10.5, with a high exchangeable sodium percentage (ESP), dense soil structure, and poor permeability. Under alkaline conditions, soil colloids carry a large number of negative charges on their surfaces, resulting in highly dispersed fine particles. During paddy field flooding and drainage, these fine colloids easily form long-term suspended fine colloids, leading not only to high turbidity in paddy field water and drainage ditches, but also, due to their large specific surface area and high surface activity, often adsorbing heavy metals, pesticide residues, antibiotics, and cationic salts, thus becoming an important colloidal-mediated non-point source pollution carrier.

[0003] In existing technologies, desulfurized gypsum is widely used as a calcium source for the improvement of saline-alkali soil, through Ca... 2+ Cation exchange with Na⁺ reduces ESP and improves soil structure; biochar, as a porous carbon material, is also used to increase soil organic carbon, improve pore structure, and adsorb pollutants. Some published literature utilizes materials such as straw, biochar, and gypsum to prepare mulch films or soil conditioners to achieve water retention, fertilization, or partial salt inhibition functions, but most of them have the following shortcomings: Simple in form and simple in structure: mostly in powder form or simple physical mixtures, lacking controllable Ca 2+ The release and spatial distribution design makes it difficult to form a stable functional layer at the soil-water interface; Insufficient functional targeting: It does not specifically address the problem of "long-term suspension of soil colloids and migration of pollutants under alkaline conditions" and lacks strategies to block colloidal channels at the soil-water interface. The application process lacks engineering adaptability: it is poorly integrated with conventional agronomic procedures such as tilling, flooding, and transplanting, making it difficult to achieve repeatable and controllable improvement effects on a large field scale. The synergy of resource utilization is not strong: farmland straw and industrial desulfurization gypsum are mostly used separately, and their synergistic effect in the saline-alkali land system is not fully utilized.

[0004] It is necessary to develop a multifunctional soil conditioner that combines calcium and sodium replacement, colloidal flocculation, water clarification, salt and pollutant adsorption, and soil structure improvement, and to endow it with a core-shell structure and Ca at the material structure level. 2+ The slow-release capability is coupled with the process of land preparation, paddy field soaking, irrigation and drainage in saline-alkali paddy fields at the application level, thereby achieving systematic regulation of soil colloids and colloid-mediated non-point source pollution. Summary of the Invention

[0005] This invention aims to solve the following problems existing in saline-alkali soil improvement materials: There is a lack of effective control measures for the long-term negatively charged suspension of soil colloids in alkaline environments, which prevents them from settling. The salts and pollutants carried by these colloids can easily enter downstream water bodies through field drainage. Calcium sources are mostly applied in powdered or gypsum-based forms. 2+ The short-term concentrated release of calcium and sodium replacement and colloidal flocculation are not coordinated in time and space, making it difficult to simultaneously improve the topsoil and control pollution at the soil-water interface. Existing technologies do not utilize core-shell structured calcium-enriched biochar particles to construct a "colloidal adsorption-flocculation-barrier layer" at the soil-water interface in paddy fields, thus lacking a systematic blockade of colloidal-mediated pollution channels.

[0006] A calcium-enriched rice straw biochar core-shell granular soil conditioner comprises: a core composed of calcium-enriched rice straw biochar; and an outer shell composed of desulfurized gypsum covering the core.

[0007] Furthermore, based on the total mass of the soil conditioner, it includes the following components: 25-40 parts of calcium-enriched rice straw biochar, 55-70 parts of desulfurized gypsum, and 2-6 parts of binder.

[0008] Furthermore, it also includes 1-8 parts of functional additives.

[0009] Furthermore, the calcium mass fraction in the core of calcium-enriched rice straw biochar is ≥5%, and the BET specific surface area is 150-450 m². 2 / g, with an average pore size of 2-20nm.

[0010] Furthermore, the mass fraction of CaSO4·2H2O in the desulfurized gypsum is ≥75%, and the desulfurized gypsum is a powder that passes through an 80-200 mesh sieve.

[0011] Furthermore, the soil conditioner is in granular form with a particle size of 1-8 mm and a bulk density of 0.9-1.4 g / cm³. 3 .

[0012] Furthermore, the binder is selected from one or more of starch, lignin sulfonate, sodium carboxymethyl cellulose, and sodium alginate; the functional additive is selected from one or more of humic acid, trace element fertilizer, and organic fertilizer.

[0013] A method for preparing calcium-enriched rice straw biochar core-shell granular soil conditioner includes the following steps: impregnating rice straw with a calcium-containing solution, pyrolyzing it under oxygen-limited conditions to obtain calcium-enriched rice straw biochar, mixing the calcium-enriched rice straw biochar with desulfurized gypsum powder and a binder, and granulating it to form core-shell granules with a desulfurized gypsum shell covering a biochar core.

[0014] Furthermore, the calcium-containing solution is a CaSO4 suspension or saturated solution prepared from desulfurized gypsum, with a solid-liquid ratio of 1:5 to 1:12 during impregnation and an impregnation time of 3 to 24 hours; the pyrolysis conditions are: holding at 450-600℃ for 1 to 3 hours.

[0015] A method for applying a calcium-enriched rice straw biochar core-shell granule soil conditioner in the improvement of saline-alkali paddy fields includes the following steps: applying the soil conditioner to the surface layer of the saline-alkali paddy field, mixing the soil conditioner into the topsoil through tillage, and then irrigating the field.

[0016] Furthermore, the application rate of soil conditioner is 1-10 t / hm. 2 By incorporating a 0-20cm topsoil layer into the saline-alkali paddy field, the soil becomes soda saline-alkali soil.

[0017] The beneficial effects of this invention are as follows: Structural Innovation – Calcium-Enriched Biochar Core-Shell Particles This invention constructs a core-shell structure with a calcium-enriched biochar core and a desulfurized gypsum shell through a process of "calcium impregnation-pyrolysis-core-shell granulation," achieving a gradient distribution and slow release of Ca within and outside the particles. Compared to a simple biochar + gypsum mixture, this method exhibits more stable and controllable Ca content in soil and aquatic environments. 2+ Release curve and higher colloidal flocculation efficiency.

[0018] Mechanism Innovation—Construction of Colloidal Barrier Layer at the Soil-Water Interface This invention utilizes the precise design of particle size and density to enable partial migration and spontaneous deposition at the soil-water interface and bottom of drainage ditches during irrigation and drainage, forming a "colloidal adsorption-flocculation-barrier layer" with calcium-enriched biochar and desulfurized gypsum as the framework. This blocks the long-term suspension of soil colloids under alkaline conditions and the migration path of pollutants they carry, providing a new spatially targeted regulation approach for the control of non-point source pollution in saline-alkali paddy fields.

[0019] Synergistic Functions – Calcium and Sodium Replacement + Colloidal Sedimentation + Pollution Reduction The soil conditioner of this invention reduces ESP and pH in the topsoil through Ca–Na exchange, thereby improving soil structure; and improves soil structure in water bodies and at the soil-water interface through Ca… 2+ Compression of the colloidal double electric layer and bridging effect promote colloidal flocculation and sedimentation, and the high specific surface area and surface functional groups of biochar adsorb salt and pollutants, thereby achieving a synergistic effect of improving soil physicochemical properties, clarifying water bodies and reducing pollution.

[0020] It has good agronomic adaptability and is easy to promote. The particle morphology and particle size range of this invention are suitable for conventional spreading and tillage equipment, without the need to modify existing agricultural machinery systems; by adjusting the application rate and the number of repeated applications, phased restoration can be achieved according to the salinity intensity, and it has good adaptability to soda saline-alkali paddy fields in cold regions.

[0021] Significant resource utilization and environmental benefits This invention enables the synergistic high-value utilization of rice straw in farmland and industrial desulfurization gypsum, reducing the environmental risks caused by straw burning and gypsum stockpiling, while improving the ecological environment of saline-alkali land and the water quality of downstream water bodies, thus possessing good comprehensive ecological and economic benefits. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the core-shell structure of the core-shell granular soil conditioner of the present invention. Detailed Implementation

[0023] A calcium-enriched rice straw biochar core-shell granular soil conditioner comprises the following components in parts by weight: Calcium-enriched rice straw biochar cores (25-40 parts); 55-70 parts of desulfurized gypsum outer shell; 2-6 parts adhesive; Optional functional additives: 1-8 parts; in: The calcium-enriched rice straw biochar core is prepared by impregnating rice straw with a calcium-containing solution and then pyrolyzing it under limited oxygen conditions at 450-600℃. It contains ≥5% Ca by mass and has a specific surface area of ​​150-450 m². 2 / g; The desulfurized gypsum shell is obtained from the by-product of flue gas desulfurization in coal-fired power plants through drying, pulverizing, and passing through an 80-200 mesh sieve, with a CaSO4·2H2O mass fraction ≥75%; The soil conditioner has a core-shell particle structure, with a particle size of 1-8mm and a bulk density of 0.9-1.4 g / cm³. 3 .

[0024] The calcium-containing solution is a CaSO4 suspension or saturated solution prepared from desulfurized gypsum, with an impregnation time of 3-24 hours and a solid-liquid ratio of 1:5-1:15.

[0025] The BET specific surface area of ​​calcium-enriched rice straw biochar cores is 200-400 m². 2 / g, pH (1:5 water extraction) is 7.5-9.0, and the average pore size is 2-20nm.

[0026] The binder is selected from one or more of starch, lignin sulfonate, sodium carboxymethyl cellulose, and sodium alginate; Functional additives include one or more of humic acid, trace element fertilizers, and organic fertilizers; The mass loss rate of the obtained core-shell particles in deionized water at 25℃ for 24 h is ≤5%.

[0027] The Ca of core-shell particles after standing in 0.01 mol / L NaCl solution for 2 h 2+ The cumulative release is 80-200 mg / L, and the Ca2+ release rate over 24 hours is [missing information]. 2+ The cumulative release was 180-450 mg / L; in simulated soda-alkali soil extract (pH 9.5, Na... + (2000 mg / L) flocculation removal rate of suspended soil colloids ≥75%, and for Na + The overall removal rate is ≥35%.

[0028] To achieve at least two of the following functions in soda-saline-alkali paddy fields: (1) Reduce soil pH and exchangeable sodium percentage (ESP); (2) Promotes the flocculation and sedimentation of negatively charged soil colloids under alkaline conditions, and reduces the turbidity of field surface water and drainage ditch water; (3) Adsorb and retain salts and pollutants that migrate with the colloid, weakening the colloid-mediated non-point source pollution pathway.

[0029] The application method of soil conditioner in saline-alkali paddy fields includes the following steps: During the land preparation period before rice planting, apply the soil conditioner at a rate of 1-10 t / hm. 2 The soil conditioner is evenly spread on the surface of saline-alkali paddy fields; rotary tillage or plowing machinery is used to mix the soil conditioner into the 0-20 cm topsoil layer; then, paddy field irrigation and rice transplanting are carried out. During multiple rounds of irrigation and drainage, some particles are rearranged and deposited at the soil-water interface and the bottom of the drainage ditch, forming a calcium-rich porous particle layer, which flocculates, adsorbs and blocks suspended soil colloids and salts.

[0030] The saline-alkali paddy fields are composed of soda-alkali soil with an original soil solution pH of 8.5-10.5 and ESP ≥ 15%. After 2-3 consecutive planting seasons at a rate of 1-5 t / hm² 2 After repeated application of the soil conditioner, the pH of the topsoil decreased by 0.3-0.8 units, the ESP decreased by 4-10 percentage points, and the content of water-stable aggregates >0.25 mm increased by 10-25%.

[0031] During a typical irrigation and drainage cycle, the turbidity of the field surface water decreased by ≥60% within 24 hours, the concentration of suspended colloids at the drainage ditch outlet decreased by ≥50%, and compared with the control field without the application of the soil conditioner, the COD and total suspended solids (TSS) of the downstream drainage water decreased by 20-40%.

[0032] A method for preparing calcium-enriched rice straw biochar core-shell granular soil conditioner includes the following steps: Calcium-containing impregnation: Cut dry rice straw into 1-3cm sections and immerse them in a calcium-containing solution prepared from desulfurized gypsum at a solid-liquid ratio of 1:5-1:12 for 3-24 hours. Pyrolysis and carbonization: The soaked rice straw is pyrolyzed at 450-600℃ under oxygen-limited conditions for 1-3 hours to obtain calcium-enriched rice straw biochar. Core-shell granulation: The calcium-enriched biochar is mixed evenly with desulfurized gypsum powder, binder and optional functional additives, and then granulated and dried to obtain core-shell particles with a desulfurized gypsum outer shell. The particle size is controlled between 1-8 mm.

[0033] Soil amendment structure and composition The calcium-enriched rice straw biochar core-shell granular soil conditioner of this invention has no limited thickness, is grayish-black porous granules, has a particle size of 1-8 mm, and a bulk density of 0.9-1.4 g / cm³. 3 .

[0034] Soil conditioner consists of the following components by weight: Calcium-enriched rice straw biochar cores (25-40 parts); 55-70 parts of desulfurized gypsum outer shell; 2-6 parts adhesive; Optional functional additives: 1-8 parts.

[0035] in: Calcium-enriched rice straw biochar core: The raw material is rice straw (preferably straw from the main varieties grown locally in rice-growing areas), which is used after removing leaves and retaining stems, and cutting into sections; it is impregnated with a calcium-containing solution prepared by desulfurization gypsum, so that Ca... 2+ Pre-adsorbed in straw tissue; after oxygen-limited pyrolysis at 450-600℃, Ca is enriched in the biochar framework and pore surface, forming a calcium-enriched biochar core; the core Ca mass fraction is ≥5%, and the BET specific surface area is 150-450 m². 2 / g, average pore size 2-20nm.

[0036] Desulfurized gypsum outer shell: The outer shell is mainly composed of desulfurized gypsum as both structural and functional component. The raw material is a byproduct of flue gas desulfurization in coal-fired power plants, which is dried, pulverized, and passed through an 80-200 mesh sieve to obtain powder, with a CaSO4·2H2O mass fraction ≥75%. During granulation, this desulfurized gypsum powder is mixed with a small amount of binder and functional additives to form a continuous or semi-continuous outer shell layer coating the calcium-rich biochar core. Furthermore, this shell acts as a Ca... 2+ The first response layer of slow-release and colloidal flocculation can rapidly provide Ca upon contact with soil or water. 2+ Immediately initiate the colloidal flocculation and sodium ion replacement process.

[0037] It should be noted that the role of binders and functional additives here is to assist in granulation, enhance the stability of the shell structure, and impart additional functions, while desulfurized gypsum is the matrix and core functional material that constitutes this shell, accounting for more than 85% of the dry basis mass of the shell.

[0038] The binder is selected from one or more of starch, lignin sulfonate, sodium carboxymethyl cellulose, and sodium alginate, and is used to enhance the stability of the core-shell structure and regulate the particle density; Functional additives include one or more of humic acid, trace element fertilizers, and organic fertilizers, used to further improve soil fertility, promote aggregate formation, and enhance the long-term improvement effect of granules.

[0039] Compared with existing technologies To demonstrate the outstanding advantages of this invention, a key performance comparison was conducted with some existing patents, and the results are shown in the table below: Table 1. Comparison of key performance characteristics of the present invention and existing technologies.

[0040] Comparative analysis: Ca 2+ Release characteristics: Patent 2017100946657 uses highly soluble calcium chloride and involves simple mixing, resulting in excessively rapid initial release. Although the release amount over 24 hours is high, it lacks sustainability and can easily lead to calcium loss. 2+ Loss. This invention achieves a smoother and more sustainable Ca loss through a core-shell structure design. 2+ Released, it is conducive to long-term improvement.

[0041] Colloids and Na + Removal efficiency: This invention achieves a colloidal removal rate (78%) and Na... + The overall removal rate (36%) was significantly better than other comparative documents, which was directly attributed to the sustained effect of the "calcium-enriched core" and the targeted barrier layer formed by the "core-shell structure" at the soil-water interface.

[0042] Structural advantages: Existing patents do not involve a clearly defined core-shell structure, and the functional components of the material are distributed singly in space, making it impossible to achieve the hierarchical response and space-targeting functions described in this invention. The core-shell structure of this invention is the key design for achieving superior performance.

[0043] Preparation method Step 1: Calcium Impregnation: Cut dried rice straw into 1-3cm sections and immerse them in a calcium-containing solution prepared with desulfurized gypsum at a solid-liquid ratio of 1:5-1:12 for 3-24 hours to allow the calcium content to increase. 2+ It enters the cell cavity and cell wall of the straw.

[0044] Step 2: Pyrolysis and carbonization: The impregnated straw is heated to 450-600℃ at 5-15℃ / min in an inert or oxygen-limited atmosphere and kept at that temperature for 1-3 hours to obtain calcium-enriched rice straw biochar with Ca element uniformly distributed in the skeleton and pores.

[0045] Step 3 Core-shell granulation: The calcium-enriched biochar obtained in Step 2 is mixed with desulfurized gypsum powder, binder and optional functional additives according to the formula ratio, granulated at an appropriate moisture content, and the particle size is controlled to be 1-8 mm. The mixture is then dried to a moisture content of ≤5% to obtain core-shell structured soil conditioner granules.

[0046] Application methods of soil conditioners in saline-alkali paddy fields Step 1: During the land preparation period before rice planting, apply the soil conditioner of this invention at a rate of 1-10 t / hm². 2 The dosage is applied to the surface layer of saline-alkali paddy fields; Step 2: Use tillage or rotary tillage machinery to plow into a 0-20cm tillage layer; Step 3 involves conventional irrigation and rice transplanting. During multiple rounds of irrigation and drainage, some of the core-shell particles remain in the topsoil, while others are rearranged and deposited at the soil-water interface and at the bottom of the drainage ditches, forming a calcium-rich porous particle layer. This achieves the following: Ca 2+ Replacement of Na + It lowers ESP and pH, promoting aggregate formation; At the soil-water interface via Ca 2+ Slow-release and porous surface adsorption flocculate and settle negatively charged soil colloids under alkaline conditions, and trap salts and pollutants carried by the colloids, thereby reducing the turbidity and pollution load of field water and drainage ditch water.

[0047] Example 1: Preparation of calcium-enriched rice straw biochar Select a common rice variety from a soda-alkali saline-alkali rice region. After harvesting, remove the leaves but keep the stems, air dry naturally until the moisture content is ≤12%, and cut into 2-3 cm sections for later use.

[0048] Weigh 10 kg of air-dried straw and add it to 100 L of a calcium-containing solution (solid-liquid ratio 1:10) prepared from desulfurized gypsum. The solution contains Ca... 2+ The concentration was 1.0 g / L, and the mixture was soaked at room temperature for 12 hours with intermittent stirring three times. After soaking, the mixture was drained until there was no obvious free water on the surface.

[0049] The impregnated straw was loaded into a tubular furnace and heated to 550℃ at 10℃ / min under nitrogen protection (50mL / min), held for 2 hours, cooled to room temperature, and the carbonized product was removed. After crushing and passing through a 40-mesh sieve, calcium-enriched rice straw biochar was obtained.

[0050] Performance testing (sample data) The specific surface area of ​​BET was determined to be 320 m² according to GB / T 19587-2017. 2 / g; The mass fraction of Ca determined by XRF was 6.8%. The pH (1:5 water extraction) was determined to be 8.3 according to GB / T 21144-2007. The average pore size is 6.5 nm (N2 adsorption-desorption method).

[0051] Example 2: Preparation of calcium-enriched biochar core-shell particles The desulfurization gypsum from a coal-fired power plant was dried at 105℃ for 12 hours, pulverized, and passed through a 120-mesh sieve. The mass fraction of CaSO4·2H2O was determined to be 78%.

[0052] Table 2 Granulation Formulation (Oven-dry weight)

[0053] Add the above components to the mixer, spray an appropriate amount of deionized water to make the moisture content reach 18-22%, and mix for 20 minutes; feed the wet material into the disc granulator, control the speed and water spray volume to make the particle size concentrated at 2-6 mm; place the particles in a 60℃ forced-air drying oven to dry for 6 hours until the moisture content is ≤5%.

[0054] Table 3. Particle properties (example data)

[0055] Table 4 Comparison of data from the experimental groups

[0056] Comparative analysis shows that using sodium lignosulfonate and starch as a binder, supplemented with sodium humate as a functional additive (i.e., the preferred formulation of this invention), achieves the best balance in terms of pellet formation rate, pellet strength, and water stability. The introduction of the functional additive (1-8 parts) has proven necessary, as it not only improves the pellet forming and processing performance but, more importantly, enhances the overall soil improvement effect of the product through its own fertilizer efficacy and agglomeration-promoting effect, synergistically with the core and shell.

[0057] Example 3: Ca 2+ Sustained-release and colloidal flocculation performance testing (laboratory simulation) Ca 2+ Slow-release test: 10g of the granules obtained in Example 2 was added to 1L of 0.01mol / L NaCl solution. Under magnetic stirring at 100rpm at 25℃, water samples were taken at different time points to determine the Ca content. 2+ concentration: Table 5 Ca 2+ Ion release concentration over time

[0058] This indicates that the granules have obvious sustained-release characteristics, providing sufficient calcium in the early stages. 2+ Supply will continue in the future.

[0059] Colloidal flocculation performance: Preparation of simulated soda saline-alkali soil extract (pH 9.5, Na...) + 2000 mg / L (suspended soil colloid 500 mg / L), take 1L and add 10g of particles from Example 2, stir gently for 30 min, let stand for 2 h, and then measure the turbidity, colloid concentration and Na+ of the supernatant. + content: Table 6 Colloidal Flocculation Performance

[0060] The colloid removal rate is approximately 78%, Na + The overall removal rate is approximately 36%, indicating that the particles of this invention have a significant flocculation and sedimentation effect on suspended colloids under alkaline conditions, and also on Na+. + It has a certain adsorption / exchange capacity.

[0061] Example 4: Field Experiment in Saline-Alkali Rice Paddies Overview of the experimental area: The experimental site is located in a soda saline-alkali rice area in western Jilin Province. The initial soil pH is 9.1, ESP is 18.5%, the content of water-stable aggregates >0.25mm is 23%, and the average turbidity of the field surface water is 180-260 NTU.

[0062] Experimental Design Treatment group: 5 t / hm of the soil conditioner of this invention was applied. 2 After spreading the fertilizer during land preparation, it should be incorporated into the 0-20cm topsoil layer. Control group: No soil conditioner was applied, and other agronomic practices were the same; Each treatment was repeated three times, with each plot having an area of ​​0.2 hm². 2 .

[0063] Key performance indicator test results (example data) Table 7 Soil physicochemical properties (0-20cm topsoil after harvest)

[0064] During a typical irrigation and drainage cycle after rice transplanting, water samples were collected from the field surface and drainage ditch outlets. The results are shown in the table below: Table 8. Water Quality of Field Surface Water and Drainage

[0065] The results show that the particles of this invention significantly reduce the turbidity of field surface water and the TSS / COD of drainage, and reduce the proportion of colloidal Fe, indicating that they have a significant weakening effect on colloidal-mediated pollution.

[0066] Table 9 Rice growth and yield (example)

[0067] The treatment group produced approximately 15.6% more yield than the control group.

[0068] Example 5: Comparison of effects of different application rates and repeated applications (two-year trial) In the same experimental area, at rates of 2, 5, and 8 t / hm respectively 2 Apply the soil conditioner of this invention according to the prescribed dosage and continue to apply it for 2 years, recording the data.

[0069] Table 10 Changes in topsoil parameters after the second year's harvest (example data):

[0070] This indicates that, under reasonable application rates, continuous application is beneficial for gradually and stably constructing a composite improvement system for the topsoil-soil-water interface.

[0071] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications, equivalent substitutions, and improvements made by those skilled in the art within the scope of the technology disclosed in the present invention, and within the spirit and principles of the present invention, should be included within the scope of protection of the present invention. Furthermore, all content not described in detail in this specification is prior art known to those skilled in the art.

Claims

1. A calcium-enriched rice straw biochar core-shell granular soil conditioner, characterized in that, include: The core is composed of calcium-rich rice straw biochar, the outer shell is composed of desulfurized gypsum, and a binder.

2. The soil conditioner according to claim 1, characterized in that, Based on the total mass of the soil conditioner, it includes the following components: 25-40 parts of calcium-enriched rice straw biochar, 55-70 parts of desulfurized gypsum, 2-6 parts of binder, and 1-8 parts of functional additives.

3. The soil conditioner according to claim 2, characterized in that, Calcium-enriched rice straw biochar contains ≥5% calcium by mass and has a BET specific surface area of ​​150-450 m². 2 / g, with an average pore size of 2-20nm.

4. The soil conditioner according to claim 3, characterized in that, The desulfurized gypsum contains ≥75% CaSO4·2H2O by mass, and the desulfurized gypsum is a powder that passes through an 80-200 mesh sieve.

5. The soil conditioner according to claim 4, characterized in that, The soil conditioner is in granular form, with a particle size of 1-8 mm and a bulk density of 0.9-1.4 g / cm³. 3 .

6. The soil conditioner according to claim 2, characterized in that, The binder is selected from one or more of starch, lignin sulfonate, sodium carboxymethyl cellulose, and sodium alginate; the functional additive is selected from one or more of humic acid, trace element fertilizer, and organic fertilizer.

7. A method for preparing a soil conditioner as described in any one of claims 1-6, characterized in that, Includes the following steps: Rice straw is impregnated with a calcium-containing solution and then pyrolyzed under limited oxygen conditions to obtain calcium-enriched rice straw biochar. The calcium-enriched rice straw biochar is then mixed with desulfurized gypsum powder and a binder and granulated to form core-shell particles with a desulfurized gypsum shell covering a biochar core.

8. The method according to claim 7, characterized in that, The calcium-containing solution is a CaSO4 suspension or saturated solution prepared from desulfurized gypsum. The solid-liquid ratio during impregnation is 1:5-1:12, and the impregnation time is 3-24 hours. The pyrolysis conditions are: heat treatment at 450-600℃ for 1-3 hours.

9. A method for applying the soil conditioner as described in any one of claims 1-6 in the improvement of saline-alkali paddy fields, characterized in that, Includes the following steps: Soil conditioner is applied to the surface layer of saline-alkali paddy fields, and then mixed into the topsoil through tillage and irrigation.

10. The application method according to claim 9, characterized in that, The application rate of soil conditioner is 1-10 t / hm. 2 By incorporating a 0-20cm topsoil layer into the saline-alkali paddy field, the soil becomes soda saline-alkali soil.

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