A biochar-based humic acid complex micro-fertilizer based on low-temperature alkali thermal modification of agricultural and forestry organic solid waste and a preparation method thereof

Abstract

The application provides a kind of biochar-based humic acid complex micro-fertilizer based on low-temperature alkali thermal modification of agricultural and forestry organic solid waste and a preparation method thereof, and belongs to the technical field of resource utilization of agricultural and forestry organic solid waste and preparation of new type of fertilizer.The preparation method is as follows: after being crushed, dried and impurity-removed, the obtained raw material powder is low-temperature baked, then mixed with an alkali solution, and constant-temperature reaction is carried out to obtain an alkali extraction liquid and an extraction residue;calcium oxide and superphosphate are added to the alkali extraction liquid to obtain a humic acid complex type medium and trace element fertilizer;superphosphate is added to the extraction residue, and constant-temperature pyrolysis is carried out in an inert atmosphere, and finally, cooling and crushing are carried out to obtain biochar;the humic acid complex type medium and trace element fertilizer and the biochar are mixed, dried and granulated to obtain a biochar-based humic acid complex micro-fertilizer.The method has simple process, low energy consumption and cost, is environmentally friendly and pollution-free, can realize efficient utilization of all components of agricultural and forestry organic solid waste, and has strong carbon sequestration capacity, excellent fertilizer efficiency and high added value.

Description

Technical Field

[0001] This invention belongs to the field of agricultural and forestry organic solid waste resource utilization and new fertilizer preparation technology, and particularly relates to a biochar-based humic acid complex micro-fertilizer based on low-temperature alkaline-thermal modification of agricultural and forestry organic solid waste and its preparation method. Background Technology

[0002] Agricultural and forestry organic solid waste includes various types such as straw, garden branches, fallen leaves, and sawdust, with an annual total output of billions of tons, making it one of the most widely sourced and largest-volume renewable biomass resources. However, the resource utilization rate of this type of organic solid waste is generally low, with most of it failing to be effectively disposed of. It is either randomly discarded in fields and woodlands or piled up on-site to form waste heaps. In some areas, to reduce disposal costs, it is even incinerated on-site. This inefficient disposal model not only causes enormous resource waste but also brings a series of problems such as environmental pollution and fire hazards. At the same time, the lack of micronutrients in agricultural production is becoming increasingly prominent. The excessive use of traditional chemical fertilizers further exacerbates soil degradation, leading to a continuous decline in soil fertility, low nutrient utilization, soil compaction, acidification, and other adverse phenomena, seriously affecting crop growth and the sustainable use of arable land. Against this backdrop, the advantages of humic acid fertilizers are becoming increasingly apparent. They can effectively improve soil structure, activate fixed nutrients in the soil, and promote crop growth and development. Biochar, on the other hand, possesses excellent carbon sequestration and soil improvement properties, and can stably store carbon elements for a long period of time, improving soil pore structure. The scientific combination of humic acid fertilizers, biochar, and trace elements to prepare novel compound fertilizers with high carbon sequestration and high efficiency has become an important technological path to solve the problem of organic solid waste disposal in agriculture and forestry and promote green agricultural development.

[0003] Soil, as the largest carbon sink in terrestrial ecosystems, accounts for over 60% of the total terrestrial carbon storage. Therefore, soil carbon replenishment and carbon sequestration for emission reduction have become core requirements for the green transformation of agriculture. Currently, farmland soils generally face the dilemma of declining carbon storage and low organic matter content, urgently requiring the development of technologies and related products that can synergistically promote soil carbon replenishment, carbon sequestration for emission reduction, and farmland quality improvement. Agricultural and forestry organic solid waste, as a high-quality biomass carbon source, is rich in convertible carbon elements and organic matter. Transforming it into functional soil carbon replenishment and sequestration products is a crucial pathway for achieving carbon sequestration and emission reduction in agriculture. This aligns perfectly with the practical needs of resource utilization of agricultural and forestry organic solid waste, addressing both the pain points of solid waste disposal and the development needs of the green transformation of agriculture, thus possessing significant industrial value and ecological significance.

[0004] Currently, the main process for preparing humic acid from agricultural and forestry organic solid waste is the traditional alkali dissolution and acid precipitation method. This process has many drawbacks: First, the liquid-to-solid ratio is high (usually 10:1 to 12:1), requiring a huge amount of water and generating a large amount of high-salt, high-COD wastewater, resulting in high environmental treatment costs. Second, the reaction temperature is high (90 to 110°C), resulting in high energy consumption and the need for a large amount of strong alkali, leading to high reagent costs. Third, strong acids need to be added for acid precipitation, further increasing costs and wastewater treatment pressure, and easily causing structural damage to humic acid and reducing its activity. Fourth, the utilization rate of agricultural and forestry organic solid waste is low, with most of the residue after humic acid extraction being discarded, failing to achieve full utilization of all components. Fifth, the prepared humic acid has poor stability, poor carbon fixation effect, and is not effectively combined with biochar and trace elements, resulting in low fertilizer added value.

[0005] Furthermore, existing processes for co-producing biochar and humic acid from agricultural and forestry organic solid waste mostly employ high-temperature pyrolysis, which not only consumes a lot of energy but also leads to a decrease in humic acid yield. Moreover, the combination of biochar and humic acid is simple, failing to form a stable complex structure, thus hindering the full realization of carbon sequestration capacity and fertilizer efficiency. Simultaneously, existing processes are mostly centralized production, requiring large equipment investments and incurring high storage and transportation costs for agricultural and forestry organic solid waste, making them unsuitable for the dispersed distribution of agricultural and forestry organic solid waste and hindering large-scale promotion. Compared with existing related technologies, there are still certain shortcomings, specifically: First, most technologies only focus on producing a single product, biochar or humic acid, from agricultural and forestry organic solid waste, failing to achieve co-production of both or synergistic integration with micronutrients, thus failing to address the dual core needs of soil carbon replenishment, carbon sequestration and emission reduction, and nutrient supply; second, some co-production technologies still use high-temperature pyrolysis or high-liquid-ratio alkali extraction processes, resulting in low carbon sequestration efficiency, high energy consumption, and a lack of complexation modification of humic acid, leading to a short carbon sequestration lifespan and difficulty in achieving long-term soil carbon replenishment; third, existing technologies... The technology has not truly solved the problem of full utilization of agricultural and forestry organic solid waste. The utilization rate of extracted residue is low, and it cannot maximize the value of biomass carbon source of agricultural and forestry organic solid waste. Moreover, it has not designed an energy consumption recycling system, resulting in insufficient economic efficiency and environmental protection. Fourth, a few carbon-fixing fertilizer technologies have a single carbon-fixing component (containing only biochar or humic acid), and have not formed a synergistic carbon-fixing system of biochar-humic acid-micronutrients. The carbon-fixing effect is limited, and the fertilizer function is singular, which cannot meet the actual needs of synergistic promotion of farmland quality improvement and carbon fixation and emission reduction.

[0006] Therefore, developing a low-temperature, low-consumption, environmentally friendly, and efficient method that can realize the full utilization of agricultural and forestry organic solid waste and co-produce high-carbon-fixing biochar and humic acid complex-type micronutrient fertilizer is of great practical significance and application value. This method can solve the problems of high energy consumption and cost, heavy environmental pressure, low resource utilization rate and fertilizer added value, and poor carbon fixation effect of existing processes. Summary of the Invention

[0007] To address the aforementioned problems in the prior art, this invention provides a biochar-based humic acid complex micro-fertilizer based on low-temperature alkaline-thermal modification of agricultural and forestry organic solid waste and its preparation method. This method employs a low-temperature semi-dry process and mixed alkaline-thermal co-production of high-carbon-fixing biochar-based humic acid complex micro-element fertilizer. The process is simple, energy-efficient, cost-effective, and environmentally friendly, enabling efficient utilization of all components of agricultural and forestry organic solid waste. The prepared compound fertilizer has strong carbon fixation capacity, excellent fertilizer efficiency, and high added value. Furthermore, it is suitable for skid-mounted mobile production mode, facilitating large-scale promotion.

[0008] To achieve the above objectives, the present invention provides the following technical solution: One of the technical solutions of the present invention: This invention provides a method for preparing biochar-based humic acid complex micro-fertilizer based on low-temperature alkaline-thermal modification of agricultural and forestry organic solid waste, comprising the following steps: (1) After crushing, drying and removing impurities from agricultural and forestry organic solid waste, the raw material powder is baked at low temperature; (2) The raw material powder baked at low temperature is mixed with an alkaline solution, and then the solid-liquid separation is carried out after constant temperature reaction to obtain alkaline extract and extraction residue; (3) Add calcium oxide and superphosphate to the alkaline extract, stir and react to form a mixed suspension of calcium humate and phosphoric acid humate, and obtain humic acid complex-type micronutrient fertilizer. (4) Add superphosphate to the extraction residue, then pyrolyze it at a constant temperature under an inert atmosphere, and finally obtain biochar after cooling and pulverizing. (5) The humic acid complex micronutrient fertilizer and biochar are mixed, dried and granulated to obtain the biochar-based humic acid complex micronutrient fertilizer.

[0009] Further, the material described in step (1) is pulverized to 20-40 mesh; The moisture content of the dried agricultural and forestry organic solid waste is ≤15%; The low-temperature baking process involves baking at 250–300 °C for 30–60 min, which causes the organic solid waste from agriculture and forestry to form an aromatic ring structure, thereby enhancing its carbon sequestration capacity.

[0010] Furthermore, the agricultural and forestry organic solid waste mentioned in step (1) is one or more of moldy, broken or damp straw, garden branches, dead branches and fallen leaves and sawdust. No additional deep drying is required before crushing. The crushing process is carried out directly, followed by drying, impurity removal and subsequent low-temperature baking.

[0011] Beneficial Effects: This invention, through pretreatment of agricultural and forestry organic solid waste by crushing, drying, impurity removal, and low-temperature baking, increases carbon fixation capacity by 30%–80% compared to direct alkali extraction. Specifically, crushing the agricultural and forestry organic solid waste to 20–40 mesh increases the contact area between the waste and the mixed alkaline solution, improving the efficiency of subsequent humic acid extraction. Drying to a moisture content ≤15% reduces the water-gas reaction between moisture and the carbon source during baking, preventing carbon source loss into the gas phase, reducing energy consumption, and avoiding wastewater generation. Impurity removal removes impurities such as soil and stones from the agricultural and forestry organic solid waste, improving product purity. Low-temperature baking (250–300 °C) degrades hemicellulose and cellulose in the waste, promoting lignin aromatization and forming stable aromatic structures. This not only improves the yield and stability of subsequent humic acid but also significantly enhances the carbon fixation capacity of the waste, laying the foundation for the preparation of high-carbon-fixing biochar. Moreover, the baking temperature of this invention is much lower than that of traditional high-temperature pyrolysis, resulting in a significant reduction in energy consumption. Agricultural and forestry organic solid waste can be selected from one or more mixtures of straw, garden branches, fallen leaves, and sawdust, offering a wide range of applications and effectively digesting various types of dispersed agricultural and forestry organic solid waste, thus solving the problem of pollution from the accumulation of different types of agricultural and forestry organic solid waste.

[0012] Further, in step (2), the liquid-solid ratio of the raw material powder and the alkaline solution after low-temperature baking is (3:1) to (5:1). The isothermal reaction is carried out at a temperature of 85–95 °C for 2–4 h, and the mixture is stirred at a speed of 60–120 rpm during the reaction. The solid-liquid separation method is to use plate compression filtration or centrifugation. If centrifugation is used, the centrifugation speed is 3000-5000 rpm and the centrifugation time is 10-20 min.

[0013] Furthermore, the alkaline solution is prepared by dissolving calcium oxide and sodium hydroxide in water; The mass concentration of calcium oxide in the alkaline solution is 2% to 3%; The mass concentration of sodium hydroxide in the alkaline solution is 1% to 2%.

[0014] Beneficial effects: This invention employs a low-temperature semi-dry process and a mixed alkali system. Compared to traditional processes, the liquid-to-solid ratio is reduced from 10:1–12:1 to 3:1–5:1, water consumption is reduced by more than 50%, achieving semi-dry production with almost no wastewater generation, significantly reducing environmental pressure. It is suitable for treating various types of agricultural and forestry organic solid waste, eliminating the need to adjust the liquid-to-solid ratio for different components of agricultural and forestry organic solid waste. The reaction temperature is reduced from 90–110 ℃ to 85–95 ℃, energy consumption is reduced by more than 30%, and the reaction is mild, avoiding damage to the humic acid structure. This invention uses a mixed alkali of CaO and NaOH to replace a single strong alkali. The price of CaO is only 1 / 5 to 1 / 10 of that of NaOH, which can greatly reduce the cost of alkali reagents. At the same time, CaO can react with the acidic components in agricultural and forestry organic solid waste in advance, promoting the release of humic acid and improving the extraction rate. NaOH can enhance the alkalinity of the system and further promote the degradation of lignin into humic acid. The synergistic effect of the two ensures that the humic acid extraction rate of different types of agricultural and forestry organic solid waste is no less than that of traditional processes.

[0015] Furthermore, the amount of calcium oxide added in step (3) is 3% to 5% of the mass of the alkaline extract; The amount of superphosphate added is 2% to 4% of the mass of the alkaline extract.

[0016] Furthermore, the temperature of the stirring reaction in step (3) is 60-80 °C and the time is 30-60 min.

[0017] Beneficial effects: This invention eliminates the acid precipitation step in traditional processes, directly adding CaO and superphosphate to the alkaline extraction solution. On one hand, CaO reacts with humic acid in the alkaline extraction solution to form calcium humate (water-insoluble and extremely difficult to degrade), while superphosphate reacts with humic acid to form phosphorus humate (dense structure and antioxidant). The two form a stable complex cross-linked structure, which not only significantly improves the stability of humic acid and extends its carbon fixation lifespan several times, but also allows calcium and phosphorus elements to bind tightly with humic acid, preventing them from being fixed by the soil and improving the utilization rate of micronutrients. On the other hand, this invention eliminates the need to add strong acid, completely eliminating the costs of acid consumption and the pollution problems of acid precipitation wastewater. Furthermore, the product contains active humic acid and usable calcium and phosphorus nutrients, which can be directly used as a micronutrient fertilizer, meeting the resource utilization needs of agricultural and forestry organic solid waste conversion products and realizing "turning waste into treasure".

[0018] Furthermore, the amount of superphosphate added in step (4) is 5% to 20% of the mass of the extraction residue; The isothermal pyrolysis is performed by heating the temperature to 450–550 °C at a heating rate of 5–10 °C / min, followed by isothermal pyrolysis for 1–2 h. The cooling to room temperature; The inert atmosphere is nitrogen or carbon dioxide, and the gas introduction rate is 0.5 to 1.0 L / min.

[0019] Furthermore, the extraction residue is a mixture of lignin, undegraded cellulose and a small amount of residual humic acid, which is mixed evenly with superphosphate before pyrolysis and then pulverized to 40-60 mesh.

[0020] Beneficial Effects: This invention uses the extracted residue (mainly lignin, undegraded cellulose, and a small amount of residual humic acid) to prepare biochar through low-temperature pyrolysis. Compared to traditional high-temperature pyrolysis, the pyrolysis temperature of 450–550 °C reduces energy consumption while preserving the active groups and pore structure of the biochar, thus enhancing its carbon fixation capacity and adsorption performance. After the extracted residue is uniformly mixed with superphosphate, it can be further pulverized to 40–60 mesh to improve pyrolysis uniformity and biochar quality, adapting to the pyrolysis requirements of extract residues with different components. Adding superphosphate as a modifier can further promote the aromatization and pore development of the biochar, while simultaneously loading phosphorus onto the surface of the biochar. This not only enhances the carbon fixation effect of the biochar but also strengthens its fertilizer function, achieving a dual effect of carbon fixation and nutrient supply. An inert atmosphere can prevent the combustion of extraction residues, ensuring the yield and quality of biochar. The carbon dioxide atmosphere can also slightly activate the biochar, further increasing its specific surface area and carbon fixation capacity, truly realizing the full utilization of extraction residues from agricultural and forestry organic solid wastes, generating no waste, and maximizing the resource value of agricultural and forestry organic solid wastes.

[0021] This invention selects superphosphate as a modifier to simultaneously achieve biochar activation and nutrient supply. Moreover, in an alkaline-thermal environment of 85-95 °C, superphosphate does not undergo violent side reactions with calcium oxide and sodium hydroxide, but only slowly releases PO4. 3- Superphosphate forms complexes with the carboxyl and hydroxyl groups of humic acid. Using a strong acidic phosphoric acid source (such as concentrated phosphoric acid) would neutralize the alkalinity of the system, disrupting the extraction environment for humic acid. Furthermore, superphosphate can fully decompose and exert its catalytic effect under pyrolysis conditions of 450-550 °C without additional heating, aligning with the core objective of low temperature and low energy consumption. Other phosphorus sources (such as phosphate rock powder) require temperatures above 800 °C for activation, resulting in double the energy consumption. This invention selects superphosphate as a modifier to reduce preparation costs while ensuring the dual functions of biochar activation and nutrient supply, thus reducing energy consumption.

[0022] Furthermore, the mass ratio of the humic acid complex-type micronutrient fertilizer and biochar in step (5) is 1:2 to 1:4; The drying process involves evaporating and drying at a temperature of 100–120 °C until the moisture content reaches 20%–30%, followed by granulation. After granulation, the product is dried further until the moisture content is ≤10%. The particle size of the granulated biochar-based humic acid complex micro-fertilizer is 2–4 mm. The granulation is performed by extrusion granulation or roller granulation.

[0023] Beneficial effects: In this invention, biochar and humic acid complexed micronutrient fertilizer are combined to form a synergistic system of biochar-humic acid-micronutrients. The high specific surface area and porous structure of biochar can adsorb humic acid and micronutrients, slowing down their release rate and achieving the effect of slow-release fertilizer. Humic acid can activate nutrients on the surface of biochar, promote crop absorption, and further enhance the carbon fixation stability of biochar. Micronutrients such as calcium and phosphorus can be directly supplied to crop growth. The synergistic effect of the three makes the prepared compound fertilizer have multiple functions such as carbon fixation, soil improvement, nutrient supply, and crop quality improvement, greatly increasing the added value. Granulation can make the product particles uniform (particle size 2-4 mm), which is convenient for storage, transportation and application, and ultimately realizes the efficient and full conversion of various agricultural and forestry organic solid wastes into high-value-added fertilizers.

[0024] Furthermore, the condensate generated during evaporation and drying in step (5) can be recycled for use in the drying of agricultural and forestry organic solid waste in step (1) or in the preparation of mixed alkaline solutions in step (2), thereby reducing water waste. The waste heat from the flue gas generated in step (4) can be used for drying of agricultural and forestry organic solid waste in step (1), reaction heating in step (2), or granulation and drying in step (5), reducing overall energy consumption by 30% to 40%, further improving the economic efficiency of the process, adapting to large-scale and multi-type agricultural and forestry organic solid waste resource utilization, and reducing the cost threshold for large-scale promotion.

[0025] The second technical solution of the present invention: The present invention also provides a biochar-based humic acid complex micro-fertilizer prepared by the preparation method of the biochar-based humic acid complex micro-fertilizer.

[0026] Furthermore, the biochar-based humic acid complex micro-fertilizer contains humic acid content ≥20%, calcium content ≥3%, phosphorus content ≥2%, biochar content ≥15%, carbon-hydrogen (H / C) ratio <0.7, and a mass residue rate ≥60% at 800℃. It has excellent carbon fixation capacity, which is 30% to 80% higher than that of traditional humic acid fertilizers. Moreover, it has a stable nutrient structure and long-lasting fertilizer effect. It can be widely used in the planting of field crops, cash crops, fruit trees, and vegetables. It is also suitable for the improvement of saline-alkali land, barren land, and compacted soil, ultimately achieving a win-win situation of carbon fixation and emission reduction, agricultural quality improvement, and resource utilization of agricultural and forestry organic solid waste.

[0027] The beneficial effects of this invention compared to the prior art are as follows: The preparation method of this invention is environmentally friendly, with low energy consumption and low cost. This invention employs a low-temperature semi-dry mixed alkali thermal extraction process, reducing the liquid-to-solid ratio to 3:1 to 5:1, generating almost no wastewater and achieving near-zero emissions. The reaction temperature is reduced to 85-95℃, and both baking and pyrolysis utilize low-temperature processes, resulting in an overall energy consumption reduction of 30%-40% compared to traditional processes. Furthermore, this invention uses a mixed alkali of CaO and NaOH instead of a single strong alkali, allowing for the recycling of the alkali extract and reducing alkali consumption by 40%-60%. This invention also eliminates the acid precipitation step, completely eliminating acid consumption costs. Simultaneously, this invention can use moldy, fragmented, and other low-quality agricultural and forestry organic solid waste as raw materials, requiring no additional deep drying before pulverization, further reducing raw material pretreatment costs. The overall process cost is 300-600 yuan / ton lower than traditional processes, reducing the difficulty of promotion.

[0028] The preparation method of this invention is highly safe and compliant. The process does not involve the excessive use of strong acids or alkalis, nor does it involve the emission of toxic or harmful gases or wastewater. The product contains no heavy metals or toxic or harmful substances, meets national fertilizer registration standards, and can be directly used in agricultural production without any harm to crops or soil. It is highly safe and compliant, and at the same time solves the environmental pollution problems caused by the incineration and accumulation of organic solid waste in agriculture and forestry, thus meeting the requirements of ecological environmental protection.

[0029] This invention achieves efficient utilization of all components of agricultural and forestry organic solid waste. Through pretreatment, alkali extraction, pyrolysis and other steps, agricultural and forestry organic solid waste achieves the co-production of humic acid, biochar and micronutrient fertilizer. The extraction residue is completely converted into high carbon-fixing biochar, and the pyrolysis gas is converted into a heat source. No waste is generated. The utilization rate of agricultural and forestry organic solid waste reaches 100%, which completely solves the problems of low resource utilization rate and environmental pollution caused by accumulation of agricultural and forestry organic solid waste. It realizes the full value utilization of resources and can digest various types of agricultural and forestry organic solid waste such as straw, garden branches, dead branches and fallen leaves on a large scale.

[0030] This invention has excellent carbon sequestration capabilities. It promotes the aromatization of agricultural and forestry organic solid waste through low-temperature baking, modifies it by adding superphosphate during biochar preparation, and forms a stable complex structure between humic acid and calcium and phosphorus, which greatly enhances the carbon sequestration capabilities of the final product and extends its carbon sequestration life to the hundred-year level. Compared with traditional humic acid fertilizers, the carbon sequestration effect is improved by 30% to 80%, which can effectively reduce agricultural carbon emissions and realize the carbon sequestration and utilization of various agricultural and forestry organic solid wastes, thus promoting the green and low-carbon transformation of agriculture.

[0031] This invention produces a fertilizer with excellent functions and high added value. The high-carbon-fixing biochar-based humic acid complexed micronutrient fertilizer combines the carbon fixation and soil improvement functions of biochar, the nutrient activation and crop growth promotion functions of humic acid, and the nutrient supply functions of micronutrients such as calcium and phosphorus, forming a synergistic effect. It can improve crop yield and quality, improve soil fertility, and increase nutrient utilization rate by 30% to 50% compared with traditional chemical fertilizers. Moreover, the product can be registered and sold as a soil conditioner containing humic acid, significantly increasing added value, realizing the high-value transformation of agricultural and forestry organic solid waste, and improving the economic benefits of the industry.

[0032] This invention features a simple and highly adaptable process. The entire process eliminates the need for autoclaves and complex purification equipment. It integrates simple equipment such as spiral propulsion continuous reactors into skid-mounted mobile equipment, enabling on-site collection, on-site conversion, and on-site sales of agricultural and forestry organic solid waste. This significantly reduces the storage and transportation costs of agricultural and forestry organic solid waste. It is well-suited to the dispersed distribution and diverse types of agricultural and forestry organic solid waste, facilitating large-scale promotion and application. It can be widely used in various scenarios where agricultural and forestry organic solid waste is generated, such as agricultural and forestry production areas, garden scenic areas, and forest farms. Detailed Implementation

[0033] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0034] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0035] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0036] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be obvious to those skilled in the art. This specification and embodiments are merely exemplary.

[0037] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0038] In the following embodiments of the present invention, the room temperature is 23±2℃. Example

[0039] A method for preparing biochar-based humic acid complex micro-fertilizer based on low-temperature alkaline-thermal modification of agricultural and forestry organic solid waste includes the following steps: (1) Raw material pretreatment: After crushing the corn stalks to 20 mesh, dry them to a moisture content of 12% and remove impurities to obtain raw material powder. Then bake them at a low temperature of 250 ℃ for 60 min to fully aromatize the corn stalks and enhance their carbon fixation capacity.

[0040] (2) Low-temperature semi-dry method for extracting humic acid by mixed alkaline thermal oxidation: The raw material powder that has been calcined at low temperature is mixed with an alkaline solution (the alkaline solution is prepared by mixing calcium oxide and sodium hydroxide with water, wherein the mass concentration of calcium oxide in the alkaline solution is 2% and the mass concentration of sodium hydroxide in the alkaline solution is 1%) at a liquid-solid ratio of 3:1, and then reacted at a constant temperature of 85 °C for 4 h. During the reaction, the mixture is stirred at a speed of 60 rpm. After the reaction is completed, a plate filter press is used to separate the solid and liquid components to obtain the alkaline extract and the extraction residue.

[0041] (3) Preparation of humic acid complexed micronutrient fertilizer by alkaline extract: Add calcium oxide and superphosphate to the above alkaline extract (the amount of calcium oxide added is 3% of the mass of the alkaline extract, and the amount of superphosphate added is 2% of the mass of the alkaline extract), and then stir and react at 60 °C for 60 min to form a mixed suspension of calcium humate and phosphoric acid humate, and obtain humic acid complexed micronutrient fertilizer.

[0042] (4) Conversion of extraction residue into high carbon-fixing biochar: Add superphosphate (the amount of superphosphate added is 5% of the extraction residue) to the above extraction residue, mix evenly and then crush to 40 mesh, introduce nitrogen gas at a gas introduction rate of 0.5 L / min, then heat to 450 ℃ at a heating rate of 5 ℃ / min, and then pyrolyze at a constant temperature for 2 h. After the pyrolysis is completed, cool to room temperature and crush again to obtain high carbon-fixing biochar, thus realizing the full utilization of corn straw extraction residue.

[0043] (5) Compound granulation: The above-mentioned humic acid complex-type micronutrient fertilizer and high carbon-fixing biochar are mixed evenly at a mass ratio of 1:2, dried at 100 ℃ to a moisture content of 20%, and then extruded and granulated to a particle size of 2 mm. After granulation, the mixture is dried at 100 ℃ to a moisture content of 8% to obtain high carbon-fixing biochar-based humic acid complex-type micronutrient fertilizer.

[0044] Example 1 shows a product prepared from corn stalks. Testing revealed the following parameters: humic acid content 22% (≥20%), calcium content 3.2% (≥3%), phosphorus content 2.1% (≥2%), biochar content 16% (≥15%), H / C ratio 0.65 (<0.7), and a residual rate of 62% (≥60%) at 800℃. The carbon fixation capacity is 30% higher than traditional humic acid fertilizers, and the nutrient utilization rate is 30% higher than traditional chemical fertilizers. The product has uniform granules, a moisture content of 8%, and no clumping, making it suitable for use as a base fertilizer for field crops. Example

[0045] A method for preparing biochar-based humic acid complex micro-fertilizer based on low-temperature alkaline-thermal modification of agricultural and forestry organic solid waste includes the following steps: (1) Raw material pretreatment: After the forestry branches are crushed to 30 mesh, they are dried to a moisture content of 10% and impurities are removed to obtain raw material powder. The raw material powder is then baked at a low temperature of 280 ℃ for 45 min to fully aromatize the forestry branches and enhance their carbon fixation capacity.

[0046] (2) Low-temperature semi-dry method for extracting humic acid by mixed alkaline thermal oxidation: The raw material powder after low-temperature calcination was mixed with an alkaline solution (the alkaline solution was prepared by mixing calcium oxide and sodium hydroxide with water, wherein the mass concentration of calcium oxide in the alkaline solution was 2.5% and the mass concentration of sodium hydroxide in the alkaline solution was 1.5%) at a liquid-solid ratio of 3.5:1, and then reacted at a constant temperature of 90 °C for 3 h. During the reaction, the mixture was stirred at a speed of 90 rpm. After the reaction, the solid and liquid were separated by centrifugation at a speed of 3000 rpm for 20 min to obtain the alkaline extract and the extraction residue.

[0047] (3) Preparation of humic acid complexed micronutrient fertilizer by alkaline extract: Add calcium oxide and superphosphate to the above alkaline extract (the amount of calcium oxide added is 4% of the mass of the alkaline extract, and the amount of superphosphate added is 3% of the mass of the alkaline extract), and then stir and react at 70 °C for 45 min to form a mixed suspension of calcium humate and phosphoric acid humate, and obtain humic acid complexed micronutrient fertilizer.

[0048] (4) Extraction residue conversion into high carbon fixation biochar: Add superphosphate (the amount of superphosphate added is 12% of the extraction residue) to the above extraction residue, mix evenly and then crush to 50 mesh, introduce carbon dioxide at a gas introduction rate of 0.8 L / min, then heat to 500 ℃ at a heating rate of 8 ℃ / min, and then pyrolyze at a constant temperature for 1.5 h. After the pyrolysis is completed, cool to room temperature and crush again to obtain high carbon fixation biochar. The flue gas generated by pyrolysis is recovered and burned for reaction heating to realize energy consumption recycling.

[0049] (5) Compound granulation: The above-mentioned humic acid complex-type micronutrient fertilizer and high carbon-fixing biochar are mixed evenly at a mass ratio of 1:3, dried at 110 ℃ to a moisture content of 25%, and then extruded and granulated to a particle size of 3 mm. After granulation, the mixture is dried at 110 ℃ to a moisture content of 7% to obtain high carbon-fixing biochar-based humic acid complex-type micronutrient fertilizer.

[0050] Example 2 shows a product prepared from forestry branches. Testing revealed the following indicators: humic acid content 25% (≥20%), calcium content 3.8% (≥3%), phosphorus content 2.8% (≥2%), biochar content 18% (≥15%), H / C ratio 0.60 (<0.7), mass residue rate at 800℃ 68% (≥60%), carbon sequestration capacity increased by 55% compared to traditional humic acid fertilizers, nutrient utilization rate increased by 40% compared to traditional chemical fertilizers; condensate and flue gas waste heat recovery utilization rate reached 80%, making it suitable for topdressing of cash crops. Example

[0051] A method for preparing biochar-based humic acid complex micro-fertilizer based on low-temperature alkaline-thermal modification of agricultural and forestry organic solid waste includes the following steps: (1) Raw material pretreatment: The tomato straw was crushed to 40 mesh and dried to a moisture content of 8%. After removing impurities, the raw material powder was obtained and baked at 300 ℃ for 30 min to fully aromatize the tomato straw and enhance its carbon fixation capacity.

[0052] (2) Low-temperature semi-dry method for extracting humic acid by mixed alkaline thermal oxidation: The raw material powder after low-temperature calcination was mixed with an alkaline solution (the alkaline solution was prepared by mixing calcium oxide and sodium hydroxide with water, wherein the mass concentration of calcium oxide in the alkaline solution was 3% and the mass concentration of sodium hydroxide in the alkaline solution was 2%) at a liquid-solid ratio of 3:1. The mixture was then reacted at a constant temperature of 95 °C for 2 h. During the reaction, the mixture was stirred at a speed of 120 rpm. After the reaction, the solid and liquid were separated by centrifugation at a speed of 5000 rpm for 10 min to obtain the alkaline extract and the extraction residue.

[0053] (3) Preparation of humic acid complexed micronutrient fertilizer by alkaline extract: Add calcium oxide and superphosphate to the above alkaline extract (the amount of calcium oxide added is 5% of the mass of the alkaline extract, and the amount of superphosphate added is 4% of the mass of the alkaline extract), and then stir and react at 80 °C for 30 min to form a mixed suspension of calcium humate and phosphoric acid humate, and obtain humic acid complexed micronutrient fertilizer.

[0054] (4) Extraction residue conversion into high carbon fixation biochar: Add superphosphate (the amount of superphosphate added is 20% of the extraction residue) to the above extraction residue, mix evenly and then crush to 60 mesh, introduce nitrogen gas at a gas introduction rate of 1.0 L / min, then heat to 450 ℃ at a heating rate of 10 ℃ / min, and then pyrolyze at a constant temperature for 1.0 h. After pyrolysis, cool to room temperature and crush again to obtain high carbon fixation biochar. The flue gas generated by pyrolysis is burned to generate heat for evaporation and drying, further reducing the overall energy consumption.

[0055] (5) Compound granulation: The above-mentioned humic acid complex-type micronutrient fertilizer and high carbon-fixing biochar are mixed evenly at a mass ratio of 1:4, dried at 120 ℃ to a moisture content of 20%, and then extruded and granulated to a particle size of 4 mm. After granulation, the mixture is dried at 120 ℃ to a moisture content of 6% to obtain the high carbon-fixing biochar-based humic acid complex-type micronutrient fertilizer.

[0056] Example 3 describes a product prepared using tomato straw as an agricultural and forestry organic solid waste raw material. Testing revealed the following indicators: humic acid content 28% (≥20%), calcium content 4.5% (≥3%), phosphorus content 3.5% (≥2%), biochar content 20% (≥15%), H / C ratio 0.55 (<0.7), and a mass residue rate of 72% (≥60%) at 800℃. The carbon sequestration capacity is 80% higher than traditional humic acid fertilizers, and the nutrient utilization rate is 50% higher than traditional chemical fertilizers. The product is suitable for improving saline-alkali land, compacted soil, and for planting various crops.

[0057] Comparative Example 1 A method for preparing a biochar-based humic acid complex micro-fertilizer based on low-temperature alkaline-thermal modification of agricultural and forestry organic solid waste differs from Example 3 in that: low-temperature baking is not performed in step (1); The remaining preparation methods are the same as in Example 3.

[0058] Testing revealed that the product prepared in Comparative Example 1 had the following specifications: humic acid content 17.2%, calcium content 3.1%, phosphorus content 2.3%, biochar content 13.8%, H / C ratio 0.82, mass residue rate at 800℃ 48%, carbon fixation capacity 35% higher than traditional humic acid fertilizer, and nutrient utilization rate 28% higher than traditional chemical fertilizer. For saline-alkali soil with an original pH of 8.6, the pH was adjusted to 8.1, resulting in a 3.5% increase in soil porosity. The product had a moisture content of 6%, a particle size of 4mm, and no obvious clumping.

[0059] Comparative Example 2 A method for preparing a biochar-based humic acid complex micro-fertilizer based on low-temperature alkaline-thermal modification of agricultural and forestry organic solid waste, differs from Example 3 in that the low-temperature baking temperature in step (1) is 350℃. The remaining preparation methods are the same as in Example 3.

[0060] Testing revealed that the product prepared in Comparative Example 2 had the following specifications: humic acid content 21.5%, calcium content 3.6%, phosphorus content 2.7%, biochar content 16.2%, H / C ratio 0.68, mass residue rate at 800℃ 56%, carbon fixation capacity 50% higher than traditional humic acid fertilizer, and nutrient utilization rate 36% higher than traditional chemical fertilizer. For saline-alkali soil with an original pH of 8.6, the pH was adjusted to 7.8, resulting in a 5.1% increase in soil porosity. The product had a moisture content of 6%, a particle size of 4mm, and no obvious clumping.

[0061] Comparative Example 3 A method for preparing a biochar-based humic acid complex micro-fertilizer based on low-temperature alkaline-thermal modification of agricultural and forestry organic solid waste, differs from Example 3 in that: the alkaline solution in step (2) is a calcium oxide solution with a mass concentration of 5%; The remaining preparation methods are the same as in Example 3.

[0062] Testing revealed that the product prepared in Comparative Example 3 had the following specifications: humic acid content 19.8%, calcium content 4.2%, phosphorus content 2.5%, biochar content 15.3%, H / C ratio 0.75, mass residue rate at 800℃ 53%, carbon fixation capacity 42% higher than traditional humic acid fertilizer, and nutrient utilization rate 32% higher than traditional chemical fertilizer. For saline-alkali soil with an original pH of 8.6, the pH was adjusted to 7.9, resulting in a 4.3% increase in soil porosity. The product had a moisture content of 6%, a particle size of 4mm, and slight localized clumping.

[0063] Comparative Example 4 A method for preparing a biochar-based humic acid complex micro-fertilizer based on low-temperature alkaline-thermal modification of agricultural and forestry organic solid waste differs from Example 3 in that: the amount of superphosphate added in step (4) is 25% of the extraction residue; The remaining preparation methods are the same as in Example 3.

[0064] The product prepared in Comparative Example 4 had an 18% increase in raw material costs due to an excess of superphosphate.

[0065] Comparative Example 5 A method for preparing a biochar-based humic acid complex micro-fertilizer based on low-temperature alkaline-thermal modification of agricultural and forestry organic solid waste, differs from Example 3 in that the mass ratio of humic acid complex micro-element fertilizer and high carbon-fixing biochar in step (5) is 1:5. The remaining preparation methods are the same as in Example 3.

[0066] Testing revealed that the product prepared in Comparative Example 5 had the following specifications: humic acid content 19.5%, calcium content 3.3%, phosphorus content 2.4%, biochar content 26.7%, H / C ratio 0.53, mass residue rate at 800℃ 75%, carbon fixation capacity increased by 68% compared to traditional humic acid fertilizers, and nutrient utilization rate increased by 34% compared to traditional chemical fertilizers. For saline-alkali soil with an original pH of 8.6, the pH was adjusted to 7.4, resulting in a 7.1% increase in soil porosity. The product had a moisture content of 6% and a particle size of 4mm. While the carbon fixation effect was slightly improved, nutrient supply was insufficient, and the crop growth-promoting effect was weakened.

[0067] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing biochar-based humic acid complex micro-fertilizer based on low-temperature alkaline-thermal modification of agricultural and forestry organic solid waste, characterized in that, Includes the following steps: (1) After crushing, drying and removing impurities from agricultural and forestry organic solid waste, the raw material powder is baked at low temperature; (2) The raw material powder baked at low temperature is mixed with an alkaline solution, and then the solid-liquid separation is carried out after constant temperature reaction to obtain alkaline extract and extraction residue; (3) Add calcium oxide and superphosphate to the alkaline extract, stir and react to form a mixed suspension of calcium humate and phosphorus humate, and obtain humic acid complex-type micronutrient fertilizer. (4) Add superphosphate to the extraction residue, then pyrolyze it at a constant temperature under an inert atmosphere, and finally obtain biochar after cooling and pulverizing. (5) The humic acid complex micronutrient fertilizer and biochar are mixed, dried and granulated to obtain the biochar-based humic acid complex micronutrient fertilizer.

2. The method for preparing biochar-based humic acid complexed micro-fertilizer according to claim 1, characterized in that, The step (1) involves pulverizing the material to 20-40 mesh. The moisture content of the dried agricultural and forestry organic solid waste is ≤15%; The low-temperature baking temperature is 250–300 °C, and the time is 30–60 min.

3. The method for preparing biochar-based humic acid complexed micro-fertilizer according to claim 1, characterized in that, The liquid-solid ratio of the raw material powder and alkaline solution after low-temperature baking in step (2) is (3:1) to (5:1). The isothermal reaction is carried out at a temperature of 85–95 °C for 2–4 h, and is stirred at a speed of 60–120 rpm during the reaction.

4. The method for preparing biochar-based humic acid complexed micro-fertilizer according to claim 3, characterized in that, The alkaline solution is prepared by dissolving calcium oxide and sodium hydroxide in water; The mass concentration of calcium oxide in the alkaline solution is 2% to 3%; The mass concentration of sodium hydroxide in the alkaline solution is 1% to 2%.

5. The method for preparing biochar-based humic acid complexed micro-fertilizer according to claim 1, characterized in that, The amount of calcium oxide added in step (3) is 3% to 5% of the mass of the alkaline extract; The amount of superphosphate added is 2% to 4% of the mass of the alkaline extract.

6. The method for preparing biochar-based humic acid complexed micro-fertilizer according to claim 1, characterized in that, The stirring reaction in step (3) is carried out at a temperature of 60–80 °C for 30–60 min.

7. The method for preparing biochar-based humic acid complexed micro-fertilizer according to claim 1, characterized in that, The amount of superphosphate added in step (4) is 5% to 20% of the mass of the extraction residue; The isothermal pyrolysis is performed by heating the temperature to 450–550 °C at a heating rate of 5–10 °C / min, followed by isothermal pyrolysis for 1–2 h. The inert atmosphere is nitrogen or carbon dioxide, and the gas introduction rate is 0.5 to 1.0 L / min.

8. The method for preparing biochar-based humic acid complexed micro-fertilizer according to claim 1, characterized in that, The mass ratio of humic acid complex-type micronutrient fertilizer to biochar in step (5) is 1:2 to 1:4; The drying process involves drying at a temperature of 100–120 °C to a moisture content of 20%–30%, followed by granulation and further drying until the product moisture content is ≤10%. The particle size of the granulated biochar-based humic acid complex micro-fertilizer is 2–4 mm.

9. A biochar-based humic acid complex micro-fertilizer prepared by the method described in any one of claims 1 to 8.

10. The biochar-based humic acid complex micro-fertilizer according to claim 9, characterized in that, The biochar-based humic acid complex micro-fertilizer contains humic acid content ≥20%, calcium content ≥3%, phosphorus content ≥2%, and biochar content ≥15%.