Humic acid type compound fertilizer synergist and its preparation method

Abstract

The present application relates to the technical field of chemical synthesis, and discloses a humic acid type compound fertilizer synergist and a preparation method thereof, wherein the synergist comprises a mineral support layer, a humic acid complex layer and a microbial agent protection layer three-layer structure. The preparation method comprises the following steps: alkali activation of mineral humic acid, determination of the activation end point by synchronous monitoring of conductivity, viscosity and oxidation-reduction potential three parameters; introduction of potassium dihydrogen phosphate and biochemical potassium fulvic acid in sequence to form a humic acid polyphosphoric acid fulvic acid complex system; granulation and drying of the base particles by a functional granulation liquid; and finally, spraying of the compound microbial powder coated by a microbial agent protection liquid on the surface of the base particles and low-temperature drying and forming.

Description

Technical Field

[0001] This invention relates to the field of chemical synthesis technology, and more specifically, to a humic acid-based compound fertilizer synergist and its preparation method. Background Technology

[0002] Compound fertilizer synergists are important functional additives for improving fertilizer utilization. Mineral-derived humic acid, containing active functional groups such as carboxyl and phenolic hydroxyl groups, is often used as a synergist in compound fertilizers.

[0003] Existing technologies typically use alkaline solutions to adjust the pH value to dissolve and activate humic acid. Then, humic acid, fulvic acid, mineral carriers, and microbial agents are physically mixed and added to the compound fertilizer production system, where the entire mixture is formed during the high-temperature granulation stage.

[0004] The aforementioned existing technologies have the following technical problems: First, using only a fixed pH value as the activation endpoint cannot effectively reflect the actual depolymerization degree of different batches of humic acid raw materials, resulting in insufficient exposure of active functional groups and limited synergistic effects; Second, humic acid lacks a stable complexing protective structure for phosphate, and phosphate easily combines with... , , The following issues contribute to the low phosphorus utilization rate: First, a fixed reaction occurs, resulting in significant phosphorus utilization. Second, a large amount of microbial agents are deactivated during high-temperature granulation and drying, and the post-coating method easily detaches due to insufficient adhesion to the particle surface. Third, the functional components are merely physically mixed, failing to form a stable multilayered functional structure, leading to discontinuous fertilizer effect release and a short duration of synergistic effect. These problems make it difficult for existing humic acid-based compound fertilizer synergists to meet practical needs in terms of overall synergistic performance. Summary of the Invention

[0005] This invention provides a humic acid-based compound fertilizer synergist and its preparation method, solving the technical problems in related technologies such as the difficulty in accurately determining the activation endpoint of humic acid, the instability of the complex structure between active components, and the large loss of activity of functional microbial agents during granulation.

[0006] This invention discloses a method for preparing a humic acid-based compound fertilizer synergist, comprising the following steps: mixing mineral-derived humic acid powder with water to form a slurry; adding sodium hydroxide for alkali activation; simultaneously monitoring the change rate of conductivity, change rate of viscosity, and redox potential of the slurry; determining the activation endpoint when all three parameters simultaneously meet the stability conditions, thus obtaining an activated humic acid slurry; and sequentially adding wood ash, potassium dihydrogen phosphate, biochemical potassium fulvate, and a mineral carrier to the activated humic acid slurry, allowing the active carboxyl groups of the activated humic acid to react with the phosphate groups to form... The first layer is a complex structure. Fulvic acid molecules enter the complex gaps through hydrogen bonds to form a second network, resulting in a complex slurry. The complex slurry is fed into a granulator and sprayed with a functional granulation solution prepared from plant-derived amino acid powder, wood vinegar, and water for granulation. After segmented low-temperature drying and sieving, the basic granules of the synergist are obtained. The compound bacterial powder is dispersed in a bacterial agent protective solution prepared from biochemical potassium fulvate and sodium alginate, and sprayed onto the surface of the basic granules of the synergist. After low-temperature fluidized drying, a bacterial agent protective layer is formed, resulting in a humic acid-type compound fertilizer synergist.

[0007] Furthermore, the humic acid source is weathered lignite, with a humic acid content of not less than 50 wt%, and is pulverized to below 20 mesh; the mass ratio of the humic acid powder to water is 1:3 to 1:5; the mass ratio of sodium hydroxide to humic acid powder is 0.08:1 to 0.15:1, and the alkali activation is carried out by stirring at 40℃ to 60℃ for 1.5h to 3h.

[0008] Furthermore, the criteria for determining the activation endpoint are as follows: the rate of change of conductivity is less than 2% of the initial conductivity value for 10 consecutive minutes; the rate of change of viscosity is less than 3% of the initial viscosity value for 10 consecutive minutes; and the fluctuation range of the redox potential is less than [missing value] for 10 consecutive minutes. .

[0009] Furthermore, the plant ash is rice husk ash or straw ash. The content is not less than 5 wt%, and the particle size is not greater than 60 mesh; the mass ratio of the plant ash to humic acid powder is 0.05:1 to 0.15:1; the mass ratio of potassium dihydrogen phosphate to humic acid powder is 0.10:1 to 0.25:1.

[0010] Furthermore, the potassium dihydrogen phosphate is prepared into an aqueous solution with a mass fraction of 20wt% to 30wt% and then slowly added dropwise to the wood ash mixture slurry. The dropwise addition rate is 3% to 6% of the total amount of potassium dihydrogen phosphate added per minute, and the pH value of the slurry is controlled to be no lower than 5.0 during the dropwise addition process.

[0011] Furthermore, the mineral carrier is composed of attapulgite powder and sodium bentonite mixed in a mass ratio of 2:1 to 4:1, and the mass ratio of the total amount of mineral carrier to humic acid powder is 0.10:1 to 0.30:1; the mass ratio of the biochemical potassium fulvate to humic acid powder is 0.06:1 to 0.12:1; the order of addition is to first add the biochemical potassium fulvate and stir for 5 to 10 minutes, and then add the mineral carrier.

[0012] Furthermore, the mass ratio of plant-derived amino acid powder, wood vinegar, and water in the functional granulation solution is 1:0.5:8 to 1:1:12; the plant-derived amino acid powder is soybean protein hydrolysate with a free amino acid content of not less than 30 wt%; the wood vinegar has an organic acid content of 3 wt% to 8 wt% and a pH value of 2.5 to 3.5; the amount of functional granulation solution injected is 8% to 15% of the dry basis mass of the complexed slurry, and the granulation temperature is not higher than 50℃.

[0013] Furthermore, the segmented low-temperature drying includes a first stage of drying at 50°C to 60°C for 20 to 30 minutes, and a second stage of drying at 65°C to 75°C for 15 to 25 minutes. After drying, the moisture content of the particles is reduced to 8% to 12%. Particles with a particle size of 1 mm to 4 mm are sieved and used as the base particles for the synergist.

[0014] Furthermore, the composite bacterial powder is composed of Bacillus subtilis powder and Bacillus lentigines powder mixed in a mass ratio of 1:1 to 2:1; the mass ratio of biochemical potassium humate, sodium alginate and water in the bacterial agent protective solution is 1:0.3:20 to 1:0.8:30; the mass ratio of the composite bacterial powder to the bacterial agent protective solution is 1:5 to 1:10; the spraying amount of the coated bacterial agent suspension is 3% to 8% of the mass of the synergist base particles, the spraying temperature is not higher than 35°C, the fluidized bed drying temperature is 30°C to 35°C, and the drying time is 10 min to 15 min.

[0015] This invention discloses a humic acid-based compound fertilizer synergist, which is prepared by the above-described preparation method.

[0016] This invention determines the endpoint of alkali activation by simultaneously monitoring three parameters: conductivity, viscosity, and redox potential. This solves the technical problem of inconsistent activation levels caused by batch variations in raw materials in traditional fixed-pH activation methods. It achieves the technical effect of observable depolymerization of humic acid molecules and assessable exposure of active functional groups. Furthermore, by constructing a humic acid-polyphosphate-fulvic acid complex system, this invention addresses the problem of phosphate fixation in soil, thereby reducing the concentration of phosphate in the soil. , , The invention achieves significant technical benefits through direct contact. The microbial agent coating step is placed after the basic granules are formed and dried. A microbial agent protective solution formed from humic acid and sodium alginate is used to pre-coat the microbial cells, solving the technical problems of significant microbial agent inactivation and easy detachment during high-temperature granulation. This results in the microbial cells not experiencing temperatures exceeding 35°C throughout the process, and enhanced adhesion between the microbial agent protective layer and the surface of the basic granules. Furthermore, the invention utilizes a three-layer structure formed by combining a multi-level porous mineral network with a humic acid complex layer. This solves the technical problem of discontinuous fertilizer release caused by the independent nature of each component, achieving a continuous fertilization effect through the interconnected release processes of the three levels. Attached Figure Description

[0017] Figure 1 This is a process flow diagram of the preparation process of the humic acid-based compound fertilizer synergist provided in the embodiments of the present invention; Figure 2 This is a schematic diagram comparing the consistency of humic acid activation provided in the embodiments of the present invention: three-parameter monitoring vs. fixed pH method; Figure 3 This is a schematic diagram comparing the phosphorus efficacy of different samples provided in the embodiments of the present invention; Figure 4 This is a schematic diagram of the bacterial agent post-coating process vs. the granulation stage mixing process provided in the embodiments of the present invention: bacterial cell survival rate and shedding rate; Figure 5 This is a schematic diagram showing a comprehensive comparison of the effective viable bacteria counts of the finished products in Examples 1-6 provided by the embodiments of the present invention; Figure 6 This is a schematic diagram of the SEM image of the finished granules of the humic acid-type compound fertilizer synergist provided in the embodiments of the present invention; Figure 7 This is a schematic diagram of the FTIR infrared spectrum of activated humic acid provided in an embodiment of the present invention; Figure 8 This is a schematic diagram of the microstructure of the bacterial agent coating layer provided in the embodiments of the present invention, obtained by TEM. Detailed Implementation

[0018] This invention discloses a humic acid-based compound fertilizer synergist and its preparation method, solving the following technical problems in the prior art: In the field of compound fertilizer synergists, mineral-derived humic acid, as a commonly used synergistic component, still faces several technical bottlenecks in its application. Firstly, traditional processes typically add humic acid directly to the compound fertilizer production system, relying solely on alkali solutions to adjust the pH for initial dissolution. This results in a large number of humic acid molecules remaining aggregated, with insufficient exposure of active sites such as carboxyl and phenolic hydroxyl groups that truly participate in nutrient adsorption and exchange, thus limiting the synergistic effect. Secondly, phosphates, once in the soil, easily react with… , , The formation of insoluble phosphorus through fixation reactions, while improving phosphate fertilizer utilization to some extent with humic acid, lacks stable complexation protection for phosphorus, resulting in still low phosphorus nutrient utilization. Thirdly, existing synergists involve adding microbial agents during the high-temperature granulation stage, leading to significant microbial inactivation during the drying process. Even with post-coating, these agents easily detach due to insufficient adsorption capacity on the granule surface. Fourthly, existing products often contain physically mixed components such as humic acid, fulvic acid, mineral carriers, and microbial agents, lacking a stable functional structure. This results in discontinuous fertilizer release and a short duration of synergistic effect.

[0019] This invention discloses a method for preparing a humic acid-based compound fertilizer synergist, comprising: Step 1: Targeted activation with humic acid The mineral humic acid is pulverized to below 20 mesh to obtain humic acid powder. The humic acid powder is mixed with water at a mass ratio of 1:3 to 1:5 and stirred to form a uniform slurry.

[0020] It should be noted that the above-mentioned mineral humic acid is mineral humic acid derived from weathered lignite, with a humic acid content of not less than 50 wt% and a moisture content of not more than 20 wt%. The preferred mass ratio of humic acid powder to water is 1:4. This ratio ensures that the slurry has suitable fluidity, facilitating the full dispersion of humic acid molecules during subsequent alkali activation.

[0021] Sodium hydroxide solid is slowly added to the slurry as an alkaline activator. The mass ratio of sodium hydroxide to humic acid powder is 0.08:1 to 0.15:1. The sodium hydroxide is added at a rate of 2% to 5% of the total amount per minute to avoid uneven degradation of humic acid molecules due to excessively high local alkali concentrations. After the sodium hydroxide is added, the mixture is stirred continuously at 40°C to 60°C for 1.5 to 3 hours.

[0022] It should be noted that the preferred mass ratio of sodium hydroxide to humic acid powder is 0.10:1 to 0.12:1. This ratio range allows for sufficient alkaline depolymerization of humic acid molecules while avoiding excessive chain breakage due to excessive sodium hydroxide. The preferred stirring reaction temperature is 50°C, and the preferred reaction time is 2 hours.

[0023] Furthermore, the stirring speed during the above-mentioned stirring reaction stage is 200 to 400 rpm to ensure that sodium hydroxide and humic acid slurry are in full contact, while avoiding excessive shear rate from damaging the molecular structure of humic acid.

[0024] Furthermore, the sodium hydroxide solid is added by slowly sprinkling it along the edge of the slurry surface while maintaining stirring, in order to prevent the sudden increase in heat generated when the sodium hydroxide solid locally accumulates and dissolves from causing local overheating of the humic acid slurry.

[0025] Furthermore, the aforementioned sodium hydroxide solid is a highly alkaline and corrosive substance. Operators must wear alkali-resistant gloves, goggles, and protective masks, and avoid dust and direct skin contact during the addition process.

[0026] Furthermore, the above-mentioned alkaline activation process must be carried out under closed or inert atmosphere protection conditions to avoid the humic acid slurry from coming into contact with oxygen in the air under alkaline high temperature conditions and undergoing oxidation side reactions, which would lead to the oxidation and consumption of active carboxyl groups and phenolic hydroxyl groups, affecting the effective number of active sites in the subsequent complexation steps.

[0027] During the alkaline activation process, the following three parameters are simultaneously monitored online to determine the activation endpoint: Step 1.1: Use a conductivity meter to detect the conductivity of the slurry in real time and record the conductivity change curve. When the conductivity change rate... When the conductivity value remains below 2% of the initial conductivity value for 10 consecutive minutes, the ion release is considered to be stable.

[0028] The rate of change of conductivity is defined as:

[0029] In the formula, The rate of change of conductivity, The conductivity value at the current moment. The conductivity value at the previous detection time. This is the initial conductivity value. This refers to the detection interval.

[0030] Step 1.2: The viscosity of the slurry was measured using an online rotational viscometer. When the viscosity change rate... When the viscosity remains below 3% of the initial viscosity for 10 consecutive minutes, the dispersion of humic acid molecules is considered to be stable.

[0031] The viscosity change rate is defined as:

[0032] In the formula, The viscosity change rate The viscosity value at the current moment. The viscosity value at the previous detection time. This is the initial viscosity value. This refers to the detection interval.

[0033] Step 1.3: Detect the oxidation-reduction potential of the slurry using an oxidation-reduction potential probe. When the fluctuation range of the oxidation-reduction potential value is lower than [value missing] for 10 consecutive minutes... When the activation reaction has entered the stable region, it is determined that the activation reaction has entered the stable region.

[0034] When all three parameters mentioned above simultaneously meet the stability conditions, the activation endpoint is considered reached, and activated humic acid slurry is obtained. At this point, the carboxyl and phenolic hydroxyl groups of the humic acid molecules are fully exposed, and the particle size of the humic acid dispersion in the activated humic acid slurry is stable. This method of determining the activation endpoint differs from the traditional method that only uses a fixed pH value as the activation endpoint, and it can ensure that the degree of depolymerization of humic acid molecules is controllable.

[0035] Furthermore, the alkaline humic acid-containing waste liquid generated after the alkaline activation reaction is completed must not be discharged directly, but must be collected and handed over to a professional waste liquid treatment agency for treatment.

[0036] Step 2: Preparation of the humic acid-polyphosphoric acid-fulvic acid complex system Add wood ash to the activated humic acid slurry obtained in step 1. The mass ratio of wood ash to humic acid powder is 0.05:1 to 0.15:1. Stir and mix at 30℃ to 45℃ for 15 min to 30 min to uniformly disperse the alkaline mineral components in the activated humic acid slurry, and obtain wood ash mixed slurry.

[0037] It should be noted that the aforementioned wood ash is rice husk ash or straw ash. The content is not less than 5 wt%, and the particle size is not greater than 60 mesh. The preferred mass ratio of wood ash to humic acid powder is 0.08:1 to 0.12:1. In this step, wood ash provides alkaline mineral cores, and its porous structure provides initial adsorption sites for subsequent nutrient complexation.

[0038] Furthermore, the stirring speed in the above-mentioned wood ash mixing step is 150 to 300 rpm to ensure that the wood ash particles are evenly dispersed in the activated humic acid slurry and to avoid sedimentation.

[0039] Potassium dihydrogen phosphate was added to the above-mentioned wood ash mixture slurry. The mass ratio of potassium dihydrogen phosphate to humic acid powder was 0.10:1 to 0.25:1. The mixture was reacted under stirring conditions for 20 to 40 minutes to activate the active carboxyl groups exposed in the humic acid slurry to adsorb phosphate ions and form the first complex structure, thus obtaining a phosphate complex slurry.

[0040] It should be noted that the potassium dihydrogen phosphate mentioned above is industrial grade potassium dihydrogen phosphate with a purity of not less than 98 wt%. The preferred mass ratio of potassium dihydrogen phosphate to humic acid powder is 0.15:1 to 0.20:1. This ratio range allows for effective complexation between the active sites of humic acid and phosphate ions, while avoiding excessive phosphate ions that could lead to an excessively low pH value in the slurry system and affect the stability of the complexation.

[0041] Furthermore, the complexation reaction temperature of the above-mentioned potassium dihydrogen phosphate and activated humic acid slurry is 30°C to 45°C, and the stirring speed is 200 to 350 rpm.

[0042] Furthermore, the potassium dihydrogen phosphate is added by preparing it into an aqueous solution with a mass fraction of 20wt% to 30wt% and then slowly dripping it into the wood ash mixture slurry. The dripping rate is 3% to 6% of the total amount of potassium dihydrogen phosphate added per minute, so as to avoid a sudden increase in local phosphate concentration that would cause an excessive instantaneous drop in the pH value of the slurry and affect the uniformity of the complex structure.

[0043] Furthermore, the pH value of the slurry must be continuously monitored during the addition of potassium dihydrogen phosphate, and controlled to be no lower than 5.0. When the pH value approaches 5.0, the addition should be stopped and an appropriate amount of wood ash or activated humic acid should be added to the slurry to restore the pH value, preventing the system from becoming too acidic, which could lead to the disintegration of the humic acid complex structure and the uncontrolled dissolution of alkaline mineral components in the wood ash.

[0044] Add biochemical potassium fulvate and mineral carrier to the above-mentioned phosphoric acid complex slurry. The mass ratio of biochemical potassium fulvate to humic acid powder is 0.06:1 to 0.12:1, and the mass ratio of total mineral carrier to humic acid powder is 0.10:1 to 0.30:1. Continue stirring and reacting for 20 to 30 minutes. Fulvic acid molecules enter the gaps of the first layer of complex structure through hydrogen bonding, forming a second layer of hydrogen bond network, and finally forming a humic acid polyphosphoric acid fulvic acid complex system to obtain the complex slurry.

[0045] It should be noted that the aforementioned biochemical potassium humate is a potassium humate salt prepared by biochemical fermentation, and the humic acid content is not less than 50 wt%. The content is not less than 10 wt%, and the water solubility is not less than 95%. The preferred mass ratio of biochemical potassium humate to humic acid powder is 0.08:1 to 0.10:1.

[0046] The mineral carrier is composed of attapulgite powder and bentonite in a mass ratio of 2:1 to 4:1. The particle size of the attapulgite powder is no greater than 200 mesh, and the specific surface area is no less than [missing information]. The aforementioned bentonite is sodium-based bentonite, with a montmorillonite content of not less than 85 wt%, a particle size not greater than 200 mesh, and a cation exchange capacity not less than [missing information]. The preferred mass ratio of attapulgite powder to bentonite is 3:1. The preferred mass ratio of total mineral carrier to humic acid powder is 0.15:1 to 0.25:1.

[0047] The needle-like crystals of attapulgite powder form a supporting framework in the complexed slurry, while the layered structure of bentonite expands upon water absorption, creating a multi-level porous network within the complexed system. Specifically, the macropores (10 μm to 50 μm in diameter) formed between the needle-like crystals of attapulgite powder facilitate rapid water absorption, while the mesopores (0.1 μm to 10 μm in diameter) formed between the bentonite layers serve as nutrient diffusion channels. Humic acid fills the mineral micropores (less than 0.1 μm in diameter) to form anchoring sites. This multi-level porous structure enables the synergist particles to exhibit a gradient release characteristic from the outside in within the soil.

[0048] Furthermore, the stirring reaction temperature after adding biochemical potassium fulvicate and mineral carrier is 30℃ to 45℃, and the stirring speed is 200 to 350 rpm, to ensure that fulvic acid molecules and mineral carrier are uniformly dispersed in the complexed slurry.

[0049] Furthermore, the order of adding the above-mentioned biochemical potassium fulvate and mineral carrier is as follows: first add the biochemical potassium fulvate and stir for 5 to 10 minutes to ensure it is fully dissolved and dispersed, and then add the mineral carrier. This is to avoid the mineral carrier particles preferentially occupying complexation sites before the fulvate molecules are evenly distributed, thus affecting the uniformity of the second layer of hydrogen bond network.

[0050] Furthermore, mineral dust will be generated during the weighing and feeding of attapulgite powder and bentonite. Operators must wear dust masks, and local dust removal devices must be provided in the feeding area to avoid inhaling mineral dust.

[0051] Step 3: Functional granulation and drying Plant-derived amino acid powder, wood vinegar, and water are mixed in a mass ratio of 1:0.5:8 to 1:1:12 and stirred until dissolved to obtain a functional granulation solution.

[0052] It should be noted that the aforementioned plant-derived amino acid powder is a soybean protein hydrolysate with a free amino acid content of not less than 30 wt% and a moisture content of not more than 5 wt%. The aforementioned wood vinegar is obtained by refining hardwood pyrolysis byproducts through double distillation, with an organic acid content of 3 wt% to 8 wt%, a pH value of 2.5 to 3.5, and a methanol content of not more than 1 wt%. The preferred mass ratio of plant-derived amino acid powder, wood vinegar, and water is 1:0.8:10.

[0053] Furthermore, the preparation temperature of the above-mentioned functional granulation solution is 20°C to 30°C, the stirring speed is 100 to 200 rpm, and the stirring time is 10 min to 20 min, so as to ensure that the plant-derived amino acid powder is fully dissolved in the mixture of water and wood vinegar.

[0054] Furthermore, the preparation sequence of the above-mentioned functional granulation solution is as follows: first, mix the wood vinegar solution with water evenly, and then add the plant-derived amino acid powder. This is to utilize the weakly acidic environment of the wood vinegar solution to promote the dissolution and dispersion of the plant-derived amino acid powder, and to avoid clumping due to excessively high local concentrations when the plant-derived amino acid powder is directly added to pure water.

[0055] Furthermore, the aforementioned wood vinegar must be confirmed to have undergone double distillation and purification before use, and the content of methanol and other low-boiling-point harmful components must meet the aforementioned specifications before it can be used for preparation. Wood vinegar has a pungent odor and contains trace amounts of harmful volatile components. The preparation of functional granulation solutions must be carried out in a fume hood or an area with local exhaust ventilation. Operators must wear masks to prevent the inhalation of volatile organic components.

[0056] Furthermore, the distillate containing low-boiling-point organic compounds such as methanol produced during the secondary distillation and refining process of wood vinegar must be collected separately and must not be directly discharged into the sewer. It must be handed over to a professional waste liquid treatment agency for treatment.

[0057] The complexed slurry obtained in step 2 is fed into a disc granulator or a rotary drum granulator, and a functional granulation liquid is sprayed in at the same time. The amount of functional granulation liquid sprayed in is 8% to 15% of the dry basis mass of the complexed slurry. Granulation is carried out under the condition that the granulation temperature is not higher than 50°C to obtain wet granules.

[0058] It should be noted that the amount of functional granulation solution injected is preferably 10% to 12% of the dry basis mass of the complexed slurry. The granulation temperature is preferably 35℃ to 45℃. The plant-derived amino acid powder in the functional granulation solution provides a binding effect and supplements the organic nitrogen source. The organic acid components in the wood vinegar solution form a weak acid bond with the humic acid complex layer during the granulation process, enhancing the granule forming strength.

[0059] The wet granules are fed into a low-temperature drying device and dried in stages: the first stage is dried at 50℃ to 60℃ for 20 to 30 minutes, and the second stage is dried at 65℃ to 75℃ for 15 to 25 minutes. After drying, the moisture content of the granules is reduced to 8% to 12%. The dried granules are then cooled to room temperature and sieved to obtain granules with a particle size of 1 mm to 4 mm, thus obtaining the base granules of the synergist.

[0060] It should be noted that the preferred temperature for the first stage of the segmented drying process is 55℃, and the preferred time is 25 minutes; the preferred temperature for the second stage is 70℃, and the preferred time is 20 minutes. This segmented drying method first removes surface moisture from the particles at a lower temperature, and then removes internal moisture at a slightly higher temperature. This avoids rapid crusting on the particle surface caused by a single high-temperature drying process, which would prevent effective removal of internal moisture. The total drying temperature should not exceed 75℃ to avoid damaging the humic acid complex structure and mineral pore network inside the particles due to high temperatures.

[0061] Furthermore, the moisture content of the dried particles was determined by a halogen moisture analyzer, with dry weight as the calculation basis.

[0062] Furthermore, the above cooling steps employ natural cooling or forced ventilation cooling, with the cooling endpoint being when the particle temperature drops to 25°C to 35°C. Screening can only be carried out after cooling to avoid particle breakage due to thermal stress during screening at higher temperatures.

[0063] Furthermore, the fine particles with a diameter less than 1 mm and the coarse particles with a diameter greater than 4 mm obtained from the above screening must be collected separately. The fine particles can be returned to the granulator as seed crystals for recycling. The coarse particles are crushed and then screened. The portion that meets the particle size requirements is included in the finished product, while the portion that does not meet the particle size requirements is returned to the granulator to reduce material loss.

[0064] Furthermore, the exhaust gas emitted during the drying process contains vapors of residual volatile organic components from the wood vinegar solution, which must be treated by condensation recovery or activated carbon adsorption before being discharged.

[0065] Step 4: Preparation of bacterial agent protection solution and bacterial agent coating Potassium humate, sodium alginate, and water are mixed in a mass ratio of 1:0.3:20 to 1:0.8:30 and stirred at 40°C to 50°C for 30 to 45 minutes to obtain a bacterial agent protective solution.

[0066] It should be noted that the sodium alginate mentioned above is food-grade sodium alginate, with a viscosity (1wt% aqueous solution, 25℃) of 200 mPa·s to 600 mPa·s and a molecular weight of [missing information]. to The preferred mass ratio of potassium humate, sodium alginate, and water is 1:0.5:25. Sodium alginate, as a natural polysaccharide film-forming component, forms a colloid with a flexible network structure in the bacterial agent protective solution, and together with humic acid, forms a protective film on the surface of the bacteria.

[0067] Furthermore, the stirring speed during the preparation of the above-mentioned bacterial agent protective solution is 100 to 200 rpm to ensure that the sodium alginate is fully swollen and dissolved, and to avoid the destruction of the colloidal network structure caused by high-speed stirring.

[0068] Furthermore, after the above-mentioned bacterial agent protective solution is prepared, it must be cooled to 25°C to 30°C before the compound bacterial powder is added, in order to avoid damage to the bacterial activity caused by the preparation temperature of 40°C to 50°C.

[0069] Bacillus subtilis powder and Bacillus thuringiensis powder were mixed at a mass ratio of 1:1 to 2:1 to obtain a compound bacterial powder. The compound bacterial powder was added to the above-mentioned bacterial agent protective solution at a mass ratio of 1:5 to 1:10. The mixture was gently stirred at a speed not exceeding 100 rpm for 15 to 20 minutes at a temperature of 25°C to 30°C to ensure that the bacteria were evenly dispersed and coated by the bacterial agent protective solution, thus obtaining a coated bacterial agent suspension.

[0070] It should be noted that the effective viable count of the above-mentioned Bacillus subtilis powder is not less than CFU / g. The effective viable count of the above-mentioned gelatinous Bacillus powder is not less than [amount missing]. CFU / g. The preferred mass ratio of Bacillus subtilis powder to gelatinous Bacillus powder is 1.5:1. The preferred mass ratio of compound bacterial powder to bacterial agent protective solution is 1:8. The stirring temperature should not exceed 30℃, and the stirring speed should not exceed 100rpm to avoid damage to the bacterial cells caused by high temperature and violent shearing.

[0071] The coated microbial agent suspension is evenly sprayed onto the surface of the synergist base particles obtained in step 3, with a spraying amount of 3% to 8% of the mass of the synergist base particles, and the spraying temperature not exceeding 35℃. After spraying, the mixture is fluidized and dried at 30℃ to 35℃ for 10 to 15 minutes to form a microbial agent protective layer on the surface of the synergist base particles, thus obtaining the finished humic acid-based compound fertilizer synergist.

[0072] It should be noted that the spraying amount is preferably 5% to 6% of the mass of the synergist base particles. The fluidized bed drying temperature is preferably 30°C, and the drying time is preferably 12 minutes. These low-temperature coating and drying conditions ensure that the bacteria do not experience high-temperature stress during the entire coating process.

[0073] Furthermore, the effective viable counts of Bacillus subtilis and Bacillus spp. in the above-mentioned humic acid-based compound fertilizer synergist were determined by plate counting method, and the determination method was carried out in accordance with the "General Technical Guidelines for Biosafety of Microbial Fertilizers" (NY / T1109).

[0074] Furthermore, the spraying rate of the above-mentioned coated microbial agent suspension is 0.5% to 1.5% of the mass of the synergist base particles per minute, so as to ensure that the coated microbial agent suspension is evenly spread on the surface of the synergist base particles and avoid local accumulation that leads to uneven thickness of the microbial agent protective layer.

[0075] Furthermore, during the above-mentioned spraying operation, the inlet air temperature of the fluidized bed shall not exceed 30°C and the relative humidity of the inlet air shall not exceed 40%, so as to avoid the protective layer of the bacterial agent from swelling and falling off prematurely due to local heating or moisture absorption on the surface of the synergist base particles.

[0076] Furthermore, the finished product of the above-mentioned humic acid-type compound fertilizer synergist must be characterized by infrared spectroscopy analysis to identify the complexation characteristic peaks of carboxyl groups, phenolic hydroxyl groups and phosphate groups in the humic acid complex layer, and the content of carbon, hydrogen, nitrogen, phosphorus and potassium in the finished product of the humic acid-type compound fertilizer synergist must be confirmed by elemental analysis to meet the target values ​​of the formula.

[0077] The final humic acid-based compound fertilizer synergist granules have a three-layer structure: the first layer is a mineral support layer, composed of a wood ash alkaline mineral core, an attapulgite needle-like skeleton, and a sodium-based bentonite layered matrix, providing the granules with physical strength and a multi-level pore network; the second layer is a humic acid complexing layer, composed of a network structure formed by activated humic acid, phosphate ions, and fulvic acid through complexation and hydrogen bonding, undertaking the functions of nutrient complexation and slow release; the third layer is a microbial agent protective layer, composed of Bacillus subtilis and gelatinous Bacillus subtilis coated with a flexible protective film formed by fulvic acid and sodium alginate, undertaking the function of microbial slow release and colonization.

[0078] Furthermore, the defective particles and screening residues generated during the preparation process of this invention are recycled back to the granulation process, resulting in high raw material utilization and low solid waste emissions. No toxic organic solvents are used in the preparation process, and the amount of alkali activator is optimized and controlled at a low level. The overall process generates relatively little waste liquid and waste gas, demonstrating good environmental adaptability.

[0079] Technical effects of the present invention To address the issue of low activation levels in humic acid, this invention does not use a fixed pH value as the activation endpoint during alkaline activation. Instead, it simultaneously monitors the rate of change of three parameters: conductivity, viscosity, and redox potential. Activation is considered complete when the rate of change of all three parameters simultaneously falls below their respective thresholds. This method makes the degree of depolymerization of humic acid molecules and the degree of exposure of active functional groups observable and measurable during alkaline activation, avoiding the inconsistency in activation levels caused by batch differences in humic acid raw materials in traditional fixed-pH activation methods.

[0080] To address the problem of low phosphorus utilization, this invention introduces potassium dihydrogen phosphate and biochemical potassium fulvate sequentially after fully activating humic acid. The exposed carboxyl groups of the activated humic acid form a first-layer complex with phosphate ions. Then, fulvate molecules enter the complexation gaps through hydrogen bonds to form a second-layer network, creating a humic acid-polyphosphate-fulvate complex system. Phosphate ions are encapsulated within this complex network and, after entering the soil, are gradually released through ion exchange, thereby reducing the interaction between phosphate ions and the soil's overall phosphorus content. , , The probability of a fixed reaction occurring upon direct contact.

[0081] To address the issue of microbial agent inactivation during granulation, this invention arranges the microbial agent coating step after the synergist base granules are formed and dried, ensuring that the microbial agent does not experience a temperature environment exceeding 35°C throughout the process. Simultaneously, a microbial agent protective solution formed from fulvic acid and sodium alginate is used to pre-coat the microbial cells, creating a flexible protective film on the surface of the synergist base granules. This physically isolates and protects the microbial cells during drying and storage, and the adhesion between the microbial agent protective layer and the humic acid complex layer on the surface of the synergist base granules reduces the risk of microbial agent detachment.

[0082] To address the issue of independent component release and discontinuous fertilizer effect, this invention combines a multi-level porous mineral network with a humic acid complexing layer. This enables the humic acid-based compound fertilizer synergist granules to exhibit a gradient release characteristic from the outside to the inside in the soil: the outer protective layer of microbial agents releases microorganisms and initiates colonization after absorbing water; the middle humic acid complexing layer gradually releases nutrients such as phosphorus and potassium under soil ion exchange; and the humic acid fixed in the inner mineral support layer continuously releases organic active substances into the rhizosphere. The release processes of these three levels are sequential in time, forming a continuous fertilization effect.

[0083] [Examples and Comparative Examples] [Example 1] 100g of humic acid powder was obtained by pulverizing mineral-derived humic acid (from weathered lignite, with a humic acid content ≥50wt% and moisture content ≤20wt%) to below 20 mesh. The humic acid powder was mixed with water at a mass ratio of 1:3, and 300g of water was added, stirring to form a uniform slurry. 8g of solid sodium hydroxide (NaOH to humic acid powder mass ratio 0.08:1) was slowly sprinkled along the edge of the slurry surface while stirring at 200rpm. The addition rate was 2% of the total amount added per minute. The reaction was continued at 40℃ with stirring for 1.5h. The rate of change in conductivity was monitored simultaneously. viscosity change rate The activation endpoint is determined when all three parameters (oxidation-reduction potential, etc.) simultaneously meet the stability conditions, thus obtaining activated humic acid slurry.

[0084] Add wood ash (rice husk ash) to the activated humic acid slurry. 5g of wood ash (content ≥ 5wt%, particle size ≤ 60 mesh) (wood ash to humic acid powder mass ratio 0.05:1) was mixed at 150 rpm for 15 min at 30℃ to obtain a wood ash slurry. 10g of potassium dihydrogen phosphate (with humic acid powder mass ratio 0.10:1) was prepared into a 20wt% aqueous solution, which was then added dropwise to the wood ash slurry at a rate of 3% of the total amount per minute. The mixture underwent a complexation reaction at 30℃ and 200 rpm for 20 min, with the pH of the slurry continuously monitored to ensure it did not fall below 5.0, thus obtaining a phosphate complexed slurry. First, add 6g of biochemical potassium humate (mass ratio of 0.06:1 to humic acid powder) to the phosphoric acid complex slurry, and stir at 200rpm for 5min to fully dissolve and disperse it. Then, add 10g of mineral carrier (mass ratio of 0.10:1 to humic acid powder, and mass ratio of attapulgite powder to bentonite 2:1), and continue stirring and reacting at 30℃ and 200rpm for 20min to obtain the complex slurry.

[0085] Plant-derived amino acid powder (soybean protein hydrolysate, free amino acid content ≥30wt%), wood vinegar (organic acid content 3wt% to 8wt%, pH 2.5 to 3.5, methanol content ≤1wt%), and water were mixed at a mass ratio of 1:0.5:8 and stirred at 100 rpm for 10 min at 20℃ to obtain a functional granulation solution. The complexed slurry was fed into a disc granulator, and the functional granulation solution (sprayed in at 8% of the dry basis mass of the complexed slurry) was injected. Granulation was carried out at 35℃ to obtain wet granules. The wet granules were dried in stages: the first stage was dried at 50℃ for 20 min, and the second stage was dried at 65℃ for 15 min. After drying, the moisture content of the granules was reduced to 8%. After cooling to 25℃, the granules were sieved, and granules with a particle size of 1 mm to 4 mm were collected to obtain the basic granules of the synergist.

[0086] Potassium humate, sodium alginate (food grade, viscosity 200 mPa·s to 600 mPa·s), and water were mixed at a mass ratio of 1:0.3:20 and dissolved by stirring at 100 rpm for 30 min at 40°C. The solution was then cooled to 25°C to obtain a preservative solution for the bacterial agent. Bacillus subtilis powder (effective viable count ≥ 100 mPa·s) was then added. CFU / g) and gelatinous Bacillus powder (effective viable count ≥ The compound bacterial powder (CFU / g) was mixed at a mass ratio of 1:1 to obtain a compound bacterial powder. The compound bacterial powder and the bacterial agent protective solution were mixed at a mass ratio of 1:5 and gently stirred at a speed not exceeding 100 rpm for 15 minutes at 25℃ to obtain a coated bacterial agent suspension. The coated bacterial agent suspension was sprayed onto the surface of the synergist base particles at a spraying amount of 3% of the base particle mass, a spraying rate of 0.5% of the base particle mass per minute, and a spraying temperature not exceeding 35℃. After spraying, the mixture was fluidized and dried at 30℃ for 10 minutes to obtain the humic acid-based compound fertilizer synergist, designated as Sample 1.

[0087] [Example 2] Take 100g of humic acid powder and mix it with water at a mass ratio of 1:5. Add 500g of water and stir to form a slurry. Stir at 400rpm and slowly sprinkle in 15g of sodium hydroxide solid (NaOH to humic acid powder mass ratio 0.15:1) at a rate of 5% of the total amount added per minute. Continue stirring and reacting at 60℃ for 3 hours. Simultaneously monitor three parameters until the stability conditions are met to determine the activation endpoint, thus obtaining the activated humic acid slurry.

[0088] Add 15g of wood ash (mass ratio 0.15:1) to the activated humic acid slurry, and mix at 300rpm for 30min at 45℃ to obtain a wood ash mixed slurry. Prepare a 30wt% aqueous solution of 25g of potassium dihydrogen phosphate (mass ratio 0.25:1), and add it dropwise at a rate of 6% of the total amount per minute. Perform a complexation reaction at 45℃ and 350rpm for 40min, continuously monitoring the pH value to ensure it does not fall below 5.0, to obtain a phosphate complexed slurry. Add 12g of biochemical potassium fulvate (mass ratio 0.12:1) to the phosphate complexed slurry, and stir at 350rpm for 10min. Then add 30g of mineral carrier (mass ratio 0.30:1, attapulgite powder to bentonite mass ratio 4:1), and continue stirring at 45℃ and 350rpm for 30min to obtain a complexed slurry.

[0089] Plant-derived amino acid powder, wood vinegar, and water were mixed at a mass ratio of 1:1:12 and stirred at 200 rpm for 20 minutes at 30°C to obtain a functional granulation solution. The complexed slurry was fed into a rotary drum granulator, and the functional granulation solution (15% of the dry weight of the complexed slurry) was sprayed in. Granulation was carried out at 50°C to obtain wet granules. The wet granules were then dried in stages: the first stage was dried at 60°C for 30 minutes, and the second stage was dried at 75°C for 25 minutes. After drying, the moisture content of the granules was reduced to 12%. After cooling to 35°C, the granules were sieved, and particles with a diameter of 1 mm to 4 mm were collected to obtain the basic granules of the synergist.

[0090] Potassium humate, sodium alginate, and water were mixed at a mass ratio of 1:0.8:30 and stirred at 200 rpm for 45 minutes at 50℃ to dissolve. The mixture was then cooled to 30℃ to obtain a preservative solution for the microbial agent. Bacillus subtilis powder and Bacillus thuringiensis powder were mixed at a mass ratio of 2:1 to obtain a compound microbial powder. The compound microbial powder was mixed with the preservative solution at a mass ratio of 1:10 and gently stirred at no more than 100 rpm for 20 minutes at 30℃ to obtain a coated microbial agent suspension. The coated microbial agent suspension was sprayed onto the surface of the synergist base granules at a spraying amount of 8% of the base granule mass, a spraying rate of 1.5% of the base granule mass per minute, and a spraying temperature not exceeding 35℃. After spraying, the mixture was fluidized and dried at 35℃ for 15 minutes to obtain the finished humic acid-based compound fertilizer synergist, designated as Sample 2.

[0091] [Example 3] Take 100g of humic acid powder and mix it with water at a mass ratio of 1:4. Add 400g of water and stir to form a slurry. Stir at 300rpm and slowly sprinkle in 11g of sodium hydroxide solid (NaOH to humic acid powder mass ratio 0.11:1) at a rate of 3.5% of the total amount per minute. Continue stirring and reacting at 50℃ for 2 hours. Simultaneously monitor three parameters until the stability conditions are met to determine the activation endpoint, thus obtaining the activated humic acid slurry.

[0092] 10g of wood ash (mass ratio 0.10:1) was added to the activated humic acid slurry and stirred at 225 rpm for 22 min at 37.5℃ to obtain a wood ash mixed slurry. 17.5g of potassium dihydrogen phosphate (mass ratio 0.175:1) was prepared into a 25wt% aqueous solution and added dropwise at a rate of 4.5% of the total amount per minute. The complexation reaction was carried out at 37.5℃ and 275 rpm for 30 min, with the pH continuously monitored to ensure it did not fall below 5.0, resulting in a phosphate complexed slurry. 9g of biochemical potassium fulvate (mass ratio 0.09:1) was first added to the phosphate complexed slurry and stirred at 275 rpm for 7.5 min. Then, 20g of mineral carrier (mass ratio 0.20:1, attapulgite powder to bentonite mass ratio 3:1) was added, and the reaction was continued at 37.5℃ and 275 rpm for 25 min to obtain the complexed slurry.

[0093] Plant-derived amino acid powder, wood vinegar, and water were mixed at a mass ratio of 1:0.8:10 and stirred at 150 rpm for 15 minutes at 25°C to obtain a functional granulation solution. The complexed slurry was fed into a disc granulator, and the functional granulation solution (11% of the dry weight of the complexed slurry) was sprayed in. Granulation was carried out at 40°C to obtain wet granules. The wet granules were dried in stages: the first stage was dried at 55°C for 25 minutes, and the second stage was dried at 70°C for 20 minutes. After drying, the moisture content of the granules was reduced to 10%. After cooling to 30°C, the granules were sieved, and particles with a diameter of 1 mm to 4 mm were collected to obtain the basic granules of the synergist.

[0094] Potassium humate, sodium alginate, and water were mixed at a mass ratio of 1:0.5:25 and stirred at 150 rpm for 37.5 min at 45℃ to dissolve. The mixture was then cooled to 27.5℃ to obtain a preservative solution for the microbial agent. Bacillus subtilis powder and Bacillus thuringiensis powder were mixed at a mass ratio of 1.5:1 to obtain a compound microbial powder. The compound microbial powder and the preservative solution were mixed at a mass ratio of 1:8 and gently stirred at no more than 100 rpm for 17.5 min at 27.5℃ to obtain a coated microbial agent suspension. The coated microbial agent suspension was sprayed onto the surface of the synergist base granules at a spraying amount of 5.5% of the base granule mass, a spraying rate of 1.0% of the base granule mass per minute, and a spraying temperature not exceeding 35℃. After spraying, the mixture was fluidized and dried at 32.5℃ for 12 min to obtain the finished humic acid-based compound fertilizer synergist, designated as Sample 3.

[0095] [Example 4] In step 1, 100g of humic acid powder was mixed with water at a mass ratio of 1:4, and 400g of water was added. While stirring at 300rpm, 10g of solid sodium hydroxide (NaOH to humic acid powder mass ratio 0.10:1) was slowly sprinkled in at a rate of 3.5% of the total amount per minute. The mixture was stirred continuously at 50℃ for 2 hours. The activation endpoint was determined after all three parameters met the stability conditions, yielding activated humic acid slurry.

[0096] In step 2, 8g of wood ash (mass ratio 0.08:1) was added to the activated humic acid slurry, and the mixture was stirred at 225 rpm for 22 min at 37.5℃ to obtain a wood ash mixed slurry. 15g of potassium dihydrogen phosphate (mass ratio 0.15:1) was prepared into a 25wt% aqueous solution and added dropwise at a rate of 4.5% of the total amount per minute. The complexation reaction was carried out at 37.5℃ and 275 rpm for 30 min, with the pH value continuously monitored to ensure it did not fall below 5.0, resulting in a phosphate complexed slurry. 8g of biochemical potassium humate (mass ratio 0.08:1) was first added to the phosphate complexed slurry, and the mixture was stirred at 275 rpm for 7.5 min. Then, 15g of mineral carrier (mass ratio 0.15:1, attapulgite powder to bentonite mass ratio 3:1) was added, and the mixture was stirred and reacted again at 37.5℃ and 275 rpm for 25 min to obtain the complexed slurry.

[0097] In step 3, plant-derived amino acid powder, wood vinegar, and water are mixed at a mass ratio of 1:0.8:10 and stirred at 150 rpm for 15 minutes at 25°C to obtain a functional granulation solution. The complexed slurry is fed into a disc granulator, and the functional granulation solution is sprayed in (the spraying amount is 10% of the dry basis mass of the complexed slurry). Granulation is carried out at 40°C to obtain wet granules. The wet granules are dried in stages: the first stage is dried at 55°C for 25 minutes, and the second stage is dried at 70°C for 20 minutes. After drying, the moisture content of the granules is reduced to 10%. After cooling to 30°C, the granules are sieved, and particles with a particle size of 1 mm to 4 mm are collected to obtain the basic granules of the synergist.

[0098] In step 4, the preparation parameters of the microbial agent protective solution are the same as in Example 3. The mass ratio of compound microbial powder to microbial agent protective solution is 1:8. The solution is gently stirred at 27.5℃ for 17.5 min to obtain a coated microbial agent suspension. The spraying amount is 5% of the mass of the base particles, the spraying rate is 1.0% of the mass of the base particles per minute, and the spraying temperature does not exceed 35℃. After spraying, the solution is fluidized and dried at 30℃ for 12 min to obtain the humic acid-based compound fertilizer synergist, designated as Sample 4.

[0099] [Example 5] In step 1, 100g of humic acid powder was mixed with water at a mass ratio of 1:4, and 400g of water was added. While stirring at 300rpm, 12g of solid sodium hydroxide (NaOH to humic acid powder mass ratio 0.12:1) was slowly sprinkled in at a rate of 3.5% of the total amount per minute. The mixture was stirred continuously at 50℃ for 2 hours. The activation endpoint was determined after all three parameters met the stability conditions, yielding activated humic acid slurry.

[0100] In step 2, 12g of wood ash (mass ratio 0.12:1) was added to the activated humic acid slurry, and the mixture was stirred at 225 rpm for 22 min at 37.5℃ to obtain a wood ash mixed slurry. 20g of potassium dihydrogen phosphate (mass ratio 0.20:1) was prepared into a 25wt% aqueous solution and added dropwise at a rate of 4.5% of the total amount per minute. The complexation reaction was carried out at 37.5℃ and 275 rpm for 30 min, with the pH value continuously monitored to ensure it did not fall below 5.0, resulting in a phosphate complexed slurry. 10g of biochemical potassium humate (mass ratio 0.10:1) was first added to the phosphate complexed slurry, and the mixture was stirred at 275 rpm for 7.5 min. Then, 25g of mineral carrier (mass ratio 0.25:1, attapulgite powder to bentonite mass ratio 3:1) was added, and the mixture was stirred and reacted again at 37.5℃ and 275 rpm for 25 min to obtain the complexed slurry.

[0101] In step 3, the preparation parameters of the functional granulation solution are the same as in Example 4. The complexed slurry is fed into a disc granulator, and the functional granulation solution (12% of the dry basis mass of the complexed slurry) is sprayed in. Granulation is carried out at 40°C to obtain wet granules. The segmented drying parameters are the same as in Example 4. After drying, the moisture content of the granules is reduced to 10%. After cooling to 30°C, the granules are sieved, and granules with a particle size of 1 mm to 4 mm are taken to obtain the basic granules of the synergist.

[0102] In step 4, the preparation parameters of the microbial agent protective solution are the same as in Example 3. The mass ratio of compound microbial powder to microbial agent protective solution is 1:8. The solution is gently stirred at 27.5℃ for 17.5 min to obtain a coated microbial agent suspension. The spraying amount is 6% of the base particle mass, the spraying rate is 1.0% of the base particle mass per minute, and the spraying temperature does not exceed 35℃. After spraying, the solution is fluidized and dried at 35℃ for 12 min to obtain the humic acid-based compound fertilizer synergist, designated as Sample 5.

[0103] [Example 6] The parameters for steps 1 to 3 are the same as in Example 3, and the basic granules of the synergist are obtained.

[0104] In step 4, potassium humate, sodium alginate, and water were mixed at a mass ratio of 1:0.5:25 and stirred at 150 rpm for 37.5 min at 45℃ to dissolve. The mixture was then cooled to 27.5℃ to obtain a protective solution for the microbial agent. Bacillus subtilis powder and Bacillus thuringiensis powder were mixed at a mass ratio of 1.5:1 to obtain a composite microbial powder. The composite microbial powder was mixed with the protective solution at a mass ratio of 1:8 and gently stirred at no more than 100 rpm for 17.5 min at 27.5℃ to obtain a coated microbial agent suspension. The spraying amount was 5.5% of the base particle mass, the spraying rate was 1.0% of the base particle mass per minute, and the spraying temperature did not exceed 35℃. After spraying, the mixture was fluidized and dried at 32.5℃ for 12 min to obtain the finished humic acid-based compound fertilizer synergist, designated as sample 6.

[0105] [Comparative Example 1] In step 1, 100g of humic acid powder was mixed with water at a mass ratio of 1:4, and 400g of water was added, stirring to form a slurry. While stirring at 300rpm, 11g of solid sodium hydroxide (mass ratio 0.11:1) was slowly added at a rate of 3.5% of the total amount per minute. The reaction was carried out at 50℃ for 2 hours. The activation endpoint was determined by measuring the pH of the slurry to reach 9.0 using a pH meter, without initiating the conductivity change rate. viscosity change rate Online monitoring of three parameters—redox potential, slurry, and oxidation-reduction potential—resulted in activated humic acid slurry.

[0106] The parameters for steps 2 to 4 are the same as in Example 3, and the humic acid-type compound fertilizer synergist is obtained, which is designated as control sample C1.

[0107] [Comparative Example 2] The parameters for step 1 are the same as in Example 3, resulting in activated humic acid slurry.

[0108] In step 2, 10g of wood ash (mass ratio 0.10:1) was added to the activated humic acid slurry, and the mixture was stirred at 225 rpm for 22 minutes at 37.5℃ to obtain a wood ash mixed slurry. The potassium dihydrogen phosphate complexation step was omitted; instead, 9g of biochemical potassium humate (mass ratio 0.09:1) was directly added to the wood ash mixed slurry, and the mixture was stirred at 275 rpm for 7.5 minutes. Then, 20g of mineral carrier (attapulgite powder to bentonite mass ratio 3:1) was added, and the mixture was stirred and reacted for another 25 minutes at 37.5℃ and 275 rpm to obtain a complexed slurry.

[0109] The parameters for steps 3 to 4 are the same as in Example 3, and the humic acid-type compound fertilizer synergist is obtained, which is designated as control sample C2.

[0110] [Comparative Example 3] The parameters for steps 1 and 2 are the same as in Example 3, resulting in a complexed slurry.

[0111] In step 3, the compound bacterial powder (Bacillus subtilis powder and Bacillus thuringiensis powder in a mass ratio of 1.5:1) is directly added to the functional granulation solution, with the same preparation parameters as in Example 3. The functional granulation solution containing the compound bacterial powder is sprayed into the complexing slurry at a rate of 11% of the dry basis mass of the complexing slurry. Granulation is carried out at 40°C to obtain wet granules. The wet granules are then dried in stages: the first stage is dried at 55°C for 25 min, and the second stage is dried at 70°C for 20 min. After drying, the moisture content of the granules is reduced to 10%. After cooling to 30°C, the granules are sieved, and particles with a diameter of 1 mm to 4 mm are collected to obtain bacterial-containing granules.

[0112] In step 4, the bacterial agent coating step is omitted, and the bacterial-containing granules are directly used as the finished product, which is recorded as control sample C3.

[0113] Experimental Objective The following three technical effects were verified: First, whether the three-parameter online monitoring method for determining the activation endpoint is superior to the traditional fixed pH method, as reflected in the consistency of humic acid activation degree and the number of exposed active functional groups; Second, whether the humic acid-phosphate complexation system can effectively reduce phosphorus fixation in the soil and improve phosphorus utilization; Third, whether the low-temperature coating process after the inoculant can significantly improve the survival rate of bacteria in the finished product and reduce the rate of inoculant shedding.

[0114] Experimental sample preparation Samples 1 to 6 and control samples C1, C2, and C3 were prepared according to the parameters of Examples 1 to 6 and Comparative Examples 1 to 3, for a total of 9 groups of samples. The amount of each group was based on 100g of humic acid powder. The complexation characteristic peaks of each batch of samples were characterized by infrared spectroscopy analysis, and the content of carbon, hydrogen, nitrogen, phosphorus, and potassium was confirmed by elemental analysis.

[0115] Experimental conditions Characterization of humic acid activation level: Fourier transform infrared spectroscopy (FTIR) was used to determine the activation level of humic acid. The area of ​​the stretching vibration peak of the nearby carboxyl group and The ratio of the peak areas of the stretching vibration of the phenolic hydroxyl group in the vicinity (denoted as peak area ratio) This ratio reflects the relative exposure of active functional groups. The same batch of humic acid feedstock was prepared five times, and the batch-to-batch coefficient of variation (CV) of the peak area ratio was calculated to evaluate activation consistency.

[0116] Phosphorus efficacy determination: 1g of each synergist sample was used to treat 100g of test soil (pH 7.2). Content 8.3 mmol / kg Content 1.2 mmol / kg Mix the soil thoroughly with water to 60% of the soil moisture content (0.9 mmol / kg), incubate at 25°C for 14 days, extract the soil solution, and determine the available phosphorus content in the solution (Olsen method). Using blank soil without added synergists as a benchmark, calculate the phosphorus availability.

[0117] Determination of cell viability and shedding rate: The number of viable bacteria in the finished granules was determined by plate counting (refer to NY / T1109), and recorded as follows: (CFU / g). The theoretical viable count in the finished granules is calculated by converting the viable count of the bacterial suspension coated with the synergist before adding the base granules. Calculate the cell survival rate ,in:

[0118] In the formula, The actual number of viable bacteria (CFU / g) in the finished product granules. This represents the theoretical viable count (CFU / g).

[0119] Determination of bacterial agent shedding rate: Take 5g of finished product granules and place them in a 50mL centrifuge tube. Add 30mL of deionized water, shake at 50rpm for 30min, and then centrifuge (3000rpm, 5min). Collect the supernatant, determine the number of viable bacteria in the supernatant, and calculate the proportion of shed bacteria to the total bacteria. This proportion is recorded as the shedding rate. :

[0120] In the formula, The number of viable bacteria in the supernatant (CFU / mL) The volume of the supernatant is (mL). The actual number of viable bacteria (CFU / g) in the finished product granules. The sample mass is in grams (g).

[0121] Experimental steps Step 1: Verification of Humic Acid Activation Consistency. Take humic acid raw materials from the same batch and prepare them five times each according to Example 3 (sample 3, online monitoring of three parameters) and Comparative Example 1 (control sample C1, fixed pH=9). Immediately sample the activated humic acid slurry obtained from each preparation, dry it to constant weight in a 60℃ forced-air drying oven, grind it, and perform FTIR analysis. Record the results. Peak area ratio, calculate the mean and CV of 5 replicates.

[0122] Step 2: Determination of phosphorus efficacy. Sample 3 (Example 3) and control sample C2 (Comparative Example 2, without phosphate complexation) were mixed with the tested soil, and a blank control group (without added synergist) was set up. Each group was repeated in 3 replicates. After incubation at 25°C for 14 days, the available phosphorus content in the soil was measured, and the phosphorus efficacy was calculated.

[0123] Step 3: Determination of cell viability and shedding rate. Take three batches of finished products from each of Sample 3 (Example 3, post-coating process) and Control Sample C3 (Comparative Example 3, bacterial powder mixed in during granulation). Use the plate count method to determine the number of viable bacteria and calculate the cell viability. and shedding rate .

[0124] Step 4: Performance Verification Across the Entire Parameter Range. A comprehensive determination of the peak area ratio of humic acid active functional groups, phosphorus efficiency, particle strength, and cell survival rate was performed on samples 1 to 6 to verify the stability of product performance within each parameter range. Particle strength was measured using a particle strength tester (compression method), and the particle breaking force (N) was recorded.

[0125] Experimental or test results Table 1 Summary of core preparation parameters for Examples 1 to 6 and Comparative Examples 1 to 3

[0126] As shown in Table 1, samples 1 to 6 cover the minimum endpoint value, maximum endpoint value and median value of each parameter. The three sets of comparative examples correspond to the single-factor control of three key variables: activation endpoint determination method, phosphate complexation step and timing of bacterial agent addition.

[0127] Table 2. Results of humic acid activation consistency and characterization of active functional groups.

[0128] As shown in Table 2, sample 3, for which the activation endpoint was determined using three-parameter online monitoring, exhibited the highest activated humic acid content. The mean was 1.42, and the coefficient of variation (CV) between batches was 3.1%; while the control sample C1, which used a fixed pH of 9 to determine the activation endpoint, The mean value was 1.18, and the batch-to-batch CV was as high as 12.7%. Compared with the fixed pH method, the three-parameter monitoring method increased the peak area ratio of active functional groups by about 20.3% and reduced the batch-to-batch consistency CV by about 75.6%. This indicates that the three-parameter online monitoring method can make the degree of depolymerization of humic acid molecules observable and measurable, effectively solving the problem of inconsistent activation degree caused by batch differences in humic acid raw materials in the traditional fixed pH method.

[0129] Table 3 Results of phosphorus efficacy determination

[0130] As shown in Table 3, the available phosphorus content in soil sample 3, containing the humic acid-phosphate complex system, was 16.4 mg / kg, with a phosphorus efficiency 97.6% higher than the control. In contrast, the available phosphorus content in control sample C2, which omitted the potassium dihydrogen phosphate complexation step, was 11.6 mg / kg, with a phosphorus efficiency 39.8% higher than the control. The phosphorus efficiency of sample 3 was approximately 41.4% higher than that of control sample C2, indicating that the complex system formed by the first layer of the humic acid-phosphate complex and the second layer of the fulvic acid hydrogen bond network can effectively reduce the phosphorus content in the soil. , , Direct contact increases the probability of a fixation reaction, significantly improving phosphorus utilization. Results from samples 4 and 5 indicate that... With a mass ratio of 0.15:1 to 0.20:1 with humic acid, the phosphorus efficacy remained between 183% and 198%, demonstrating stable performance.

[0131] Table 4 Results of bacterial cell survival rate and inoculant shedding rate

[0132] As shown in Table 4, samples 3 to 6, which were coated with microbial agents using a low-temperature process, had an effective viable bacteria count in the finished product. to Between CFU / g, the bacterial cell survival rate was 80.4% to 84.8%, and the bacterial agent shedding rate was 4.0% to 4.5%; while the control sample C3, which used a process of mixing bacterial powder into the granulation stage, had a finished product with only a few effective viable bacteria. With a CFU / g concentration, the cell survival rate was 11.1%, while the bacterial agent detachment rate was as high as 18.7%. The post-coating process improved the cell survival rate by approximately 64.4 to 73.7 percentage points compared to the granulation stage mixing process, and reduced the bacterial agent detachment rate by approximately 14.2 to 14.7 percentage points. This indicates that placing the bacterial agent coating step after the synergist base granules have been formed and dried, combined with the flexible protective film formed by fulvic acid and sodium alginate, can effectively prevent significant cell inactivation during the high-temperature drying stage, and reduce the risk of bacterial agent detachment through the adhesion between the bacterial agent protective layer and the humic acid complex layer.

[0133] Based on the above experimental results, the samples from Examples 1 to 6 were superior to the control samples of the three comparative examples in terms of humic acid activation consistency, phosphorus efficiency, cell survival rate, and particle functional integrity. The three comparative experiments respectively demonstrated that: the three-parameter online monitoring activation endpoint determination method is a necessary condition to ensure the consistency of humic acid activation and the full exposure of active functional groups; the humic acid-phosphate complexation system is a key step in improving phosphorus efficiency; and the low-temperature coating process after inoculum treatment is the core process arrangement to ensure the survival rate of the finished cell and reduce the inoculum shedding rate. Examples 1 to 6 covered the minimum, maximum, and intermediate values ​​of each process parameter, and the performance of each group of samples was within a reasonable range, verifying the effectiveness and stability of the process parameter range of the present invention.

[0134] The embodiments of the present invention have been described above. However, the embodiments are not limited to the specific implementation methods described above. The specific implementation methods described above are merely illustrative and not restrictive. Those skilled in the art can make more equivalent embodiments under the guidance of the present embodiments, and all of them are within the protection scope of the present embodiments.

Claims

1. A method for preparing a humic acid-based compound fertilizer synergist, characterized in that, Includes the following steps: Mineral humic acid powder is mixed with water to form a slurry. Sodium hydroxide is added for alkaline activation. The change rate of conductivity, the change rate of viscosity, and the redox potential of the slurry are monitored simultaneously. When the three parameters meet the stability conditions at the same time, the activation endpoint is determined, and activated humic acid slurry is obtained. Wood ash, potassium dihydrogen phosphate, biochemical potassium fulvate and mineral carrier are added sequentially to activated humic acid slurry, so that the active carboxyl groups of activated humic acid and phosphate groups form the first layer of complex structure, and fulvic acid molecules enter the complex gap through hydrogen bonds to form the second layer of network, thus obtaining complex slurry. The complexed slurry is fed into a granulator, and a functional granulation liquid prepared from plant-derived amino acid powder, wood vinegar and water is sprayed in for granulation. After segmented low-temperature drying and sieving, the basic granules of the synergist are obtained. The compound microbial powder is dispersed in a microbial agent protective solution prepared from biochemical potassium humate and sodium alginate, sprayed onto the surface of the synergist base particles, and dried at low temperature to form a microbial agent protective layer, thus obtaining a humic acid-type compound fertilizer synergist.

2. The preparation method of a humic acid-based compound fertilizer synergist according to claim 1, characterized in that, The humic acid source is weathered lignite, with a humic acid content of not less than 50 wt%, and is pulverized to below 20 mesh; the mass ratio of the humic acid powder to water is 1:3 to 1:5; the mass ratio of sodium hydroxide to humic acid powder is 0.08:1 to 0.15:1, and the alkali activation is carried out by stirring at 40℃ to 60℃ for 1.5h to 3h.

3. The preparation method of a humic acid-based compound fertilizer synergist according to claim 1, characterized in that, The activation endpoint is determined as follows: the rate of change of conductivity is less than 2% of the initial conductivity value for 10 consecutive minutes; the rate of change of viscosity is less than 3% of the initial viscosity value for 10 consecutive minutes; and the fluctuation range of the redox potential is less than [missing value] for 10 consecutive minutes. .

4. The preparation method of a humic acid-based compound fertilizer synergist according to claim 1, characterized in that, The plant ash is rice husk ash or straw ash. The content is not less than 5 wt%, and the particle size is not greater than 60 mesh; the mass ratio of the plant ash to humic acid powder is 0.05:1 to 0.15:1; the mass ratio of potassium dihydrogen phosphate to humic acid powder is 0.10:1 to 0.25:

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5. The preparation method of a humic acid-based compound fertilizer synergist according to claim 1, characterized in that, The potassium dihydrogen phosphate is prepared into an aqueous solution with a mass fraction of 20wt% to 30wt% and then slowly added dropwise to the wood ash mixture. The dropwise addition rate is 3% to 6% of the total amount of potassium dihydrogen phosphate added per minute, and the pH value of the mixture is controlled to be no lower than 5.0 during the dropwise addition process.

6. The method for preparing a humic acid-based compound fertilizer synergist according to claim 1, characterized in that, The mineral carrier is composed of attapulgite powder and sodium bentonite mixed in a mass ratio of 2:1 to 4:1, and the total mass ratio of the mineral carrier to the humic acid powder is 0.10:1 to 0.30:1; the mass ratio of the biochemical potassium fulvate to the humic acid powder is 0.06:1 to 0.12:1; the order of addition is to first add the biochemical potassium fulvate and stir for 5 to 10 minutes, and then add the mineral carrier.

7. The preparation method of a humic acid-based compound fertilizer synergist according to claim 1, characterized in that, The mass ratio of plant-derived amino acid powder, wood vinegar, and water in the functional granulation solution is 1:0.5:8 to 1:1:12; the plant-derived amino acid powder is soybean protein hydrolysate with a free amino acid content of not less than 30 wt%; the wood vinegar has an organic acid content of 3 wt% to 8 wt% and a pH value of 2.5 to 3.5; the amount of functional granulation solution injected is 8% to 15% of the dry basis mass of the complexed slurry, and the granulation temperature is not higher than 50℃.

8. The preparation method of a humic acid-based compound fertilizer synergist according to claim 1, characterized in that, The segmented low-temperature drying includes a first stage of drying at 50°C to 60°C for 20 to 30 minutes, and a second stage of drying at 65°C to 75°C for 15 to 25 minutes. After drying, the moisture content of the particles is reduced to 8% to 12%. Particles with a particle size of 1 mm to 4 mm are screened and used as the base particles for the synergist.

9. The preparation method of a humic acid-based compound fertilizer synergist according to claim 1, characterized in that, The compound bacterial powder is composed of Bacillus subtilis powder and Bacillus lentigines powder mixed in a mass ratio of 1:1 to 2:1; the mass ratio of potassium humate, sodium alginate and water in the bacterial agent protective solution is 1:0.3:20 to 1:0.8:30; the mass ratio of the compound bacterial powder to the bacterial agent protective solution is 1:5 to 1:10; the spraying amount of the coated bacterial agent suspension is 3% to 8% of the mass of the synergist base particles, the spraying temperature is not higher than 35℃, the fluidized bed drying temperature is 30℃ to 35℃, and the drying time is 10 min to 15 min.

10. A humic acid-based compound fertilizer synergist prepared by the preparation method of a humic acid-based compound fertilizer synergist according to any one of claims 1 to 9.

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