Seaweed-based composite water-soluble fertilizer and preparation method thereof
By encapsulating Bacillus subtilis gel microspheres and modified thiosalicylic acid metal complexes in a porous carrier of seaweed charcoal, the problem of heavy metal pollution in soil along the Yangtze River Plain was solved, achieving the resource utilization of seaweed and the effect of environmentally friendly slow-release fertilizer.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- 烟台绿云生物科技有限公司
- Filing Date
- 2026-01-30
- Publication Date
- 2026-04-14
AI Technical Summary
The soil in the plains along the Yangtze River is severely polluted with heavy metals. Existing chemical remediation agents are prone to residues, which affect the quality of rice and cause secondary pollution. There is a lack of green remediation technologies that utilize seaweed resources as a solution.
A porous carrier of seaweed charcoal is used to encapsulate Bacillus subtilis gel microspheres, which are then combined with castor oil polyether polyol and modified thiosalicylic acid metal complex to form an environmentally friendly composite water-soluble fertilizer that achieves slow release and heavy metal adsorption.
It enables the resource utilization of marine biomass resources, avoids chemical additive residues, protects microbial activity, reduces soil heavy metal content, and achieves precise nutrient release and heavy metal adsorption.
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Abstract
Description
Technical Field
[0001] This invention belongs to the field of functional fertilizer technology, specifically a seaweed-based compound water-soluble fertilizer and its preparation method. Background Technology
[0002] In the plains along the Yangtze River, under suitable climate and farming conditions, the soil has high fertility, rich in organic matter and various nutrients such as nitrogen, phosphorus, and potassium, providing ample nutrients for crop growth. The plains along the Yangtze River also have abundant water resources and excellent irrigation conditions, which are conducive to crop growth and agricultural production, providing a good soil environment for rice growth.
[0003] Soils in the plains along the Yangtze River are susceptible to pollution by various heavy metals. With the acceleration of industrialization and urbanization, industrial wastewater, domestic sewage, and agricultural non-point source pollution are constantly being discharged into the soil and water bodies, leading to increasingly serious soil pollution problems. The content and activity of heavy metals in the soil will affect the absorption and accumulation of them by rice. During the accumulation process, heavy metals will enter the root system of plants and then be transported to other parts, such as stems, leaves, and grains, thereby affecting the quality and yield of rice. Rice contaminated with heavy metals will promote the accumulation of harmful substances, and these harmful substances will cause harm to human health through the food chain.
[0004] To address soil heavy metal pollution, current technologies primarily employ chemical remediation agents for soil improvement. However, these chemically synthesized additives are prone to leaving residues in the soil, causing secondary pollution and disrupting the original ecological structure. Meanwhile, green technologies such as bioremediation and biomass-based remediation are gradually becoming research hotspots. Seaweed, as a widely available and inexpensive renewable marine biomass resource, possesses carbonization products with abundant porous structures and surface active sites, demonstrating promising potential for heavy metal adsorption.
[0005] Currently, there is no technology that can utilize marine biomass resources to construct a green remediation system that specifically addresses heavy metal pollution in the plains along the Yangtze River, thereby achieving both the resource utilization of marine biomass and avoiding the risk of soil residue from chemical additives. Summary of the Invention
[0006] The purpose of this invention is to provide a seaweed-based composite water-soluble fertilizer and its preparation method. By using a composite seaweed char porous carrier to adsorb and fix gel microspheres encapsulated with Bacillus subtilis, it can achieve good slow-release effect. Seaweed is a renewable marine biomass resource with wide availability and relatively low cost. Carbonizing seaweed to prepare seaweed char realizes the resource utilization of marine biomass. At the same time, the introduction of Bacillus subtilis functional components and castor oil polyether polyol are both environmentally friendly substances, avoiding the soil residue risks caused by chemically synthesized additives.
[0007] The objective of this invention can be achieved through the following technical solutions: A method for preparing a seaweed-based compound water-soluble fertilizer includes the following steps: Step 1: Dry and sieve the seaweed, then calcine it to prepare seaweed char. Using seaweed char as a carrier, castor oil polyether polyol and isocyanate as raw materials, polymerize them on the surface of the seaweed char and then calcine them to obtain a porous seaweed char carrier.
[0008] Step 2: A hydroxymethyl intermediate is formed by the condensation of one end amino group of 2,5-diaminoterephthalic acid with formaldehyde. After protonation, an imine ion is generated. The imine ion attacks the carbon in the thiosalicylic acid structure to obtain modified thiosalicylic acid. The modified thiosalicylic acid undergoes a coordination reaction with the iron ions in ferric chloride to form a metal complex. Using a porous seaweed carbon carrier as a support, the metal complex is loaded into the pores to obtain a composite porous seaweed carbon carrier.
[0009] Step 3: Sodium alginate and calcium chloride undergo a cross-linking reaction to form a gel network, which encapsulates Bacillus subtilis to form sodium alginate microcapsules. Then, after the remaining amino groups in the composite seaweed char porous carrier react with the carboxyl groups in the sodium alginate microcapsules, seaweed-based composite microcapsules are obtained.
[0010] Step 4: Add seaweed-based composite microcapsules, humic acid, urea and potassium sulfate to a mixer and mix evenly to obtain seaweed-based composite water-soluble fertilizer.
[0011] Furthermore, the mass ratio of seaweed-based composite microcapsules, humic acid, urea, and potassium sulfate is 50-60:10-12:12-14:3-4.
[0012] Furthermore, the specific preparation steps for seaweed charcoal are as follows: Seaweed is dried to make seaweed powder, which is then sieved to a fineness of 100-120 mesh using a vibrating sieve. The powder is then dried in a forced-air drying oven at 100-110℃ for 24-26 hours to obtain pretreated seaweed powder. The pretreated seaweed powder is placed in a reaction vessel, and nitrogen gas is introduced at a flow rate of 150-160 cm / min for 30-40 minutes. The mixture is then heated to 500-550℃ and held at that temperature for 1-2 hours. After natural cooling, seaweed char is obtained.
[0013] Furthermore, the specific preparation steps of the seaweed char porous carrier are as follows: Castor oil polyether polyol, seaweed charcoal, and N,N-dimethylformamide were added to a reaction vessel and stirred for 40-50 minutes at 20-25°C and 500-600 rpm. Then, triethylenediamine, dibutyltin dilaurate, 1,4-butanediol, and isocyanate were added, and stirring was continued for another 40-50 minutes. The mixture was then poured into a mold, heated to 120-130°C, and stirred at 80-90 rpm for 10-12 minutes to mature. After demolding, the mixture was allowed to cool naturally to room temperature and then vacuum dried at 60-70°C for 1-2 hours. Finally, it was transferred to a muffle furnace and calcined at 500-550°C for 1-2 hours under a nitrogen atmosphere to obtain a porous seaweed charcoal carrier.
[0014] Furthermore, the ratio of castor oil polyether polyol, seaweed charcoal, N,N-dimethylformamide, triethylenediamine, dibutyltin dilaurate, 1,4-butanediol, and isocyanate is 200-300mL: 50-52g: 800-900mL: 0.5-0.8g: 1-1.2g: 0.4-0.5mL: 200-300mL.
[0015] Furthermore, the specific preparation steps for modified thiosalicylic acid are as follows: Thiosyl salicylic acid and deionized water were added to a reaction vessel and stirred for 40-50 min at 20-25℃ and 500-600 r / min. Then, 2,5-diaminoterephthalic acid was added and stirring was continued for 1-2 h. Then, 20-25% sulfuric acid solution was added to adjust the pH value to 3-4. The mixture was heated to 70-80℃, and 37% formaldehyde solution was added dropwise. The reaction was continued for 4 h. The mixture was then filtered under reduced pressure. The filter cake was washed 2-4 times with deionized water and anhydrous ethanol, respectively, and dried under vacuum at 60-70℃ for 1-2 h to obtain modified thiosalicylic acid.
[0016] Furthermore, the ratio of the amounts of thiosalicylic acid, deionized water, 2,5-diaminoterephthalic acid, sulfuric acid solution, and formaldehyde solution is 80-90g: 500-600mL: 40-50g: 15-17mL: 120-140mL.
[0017] Furthermore, the specific preparation steps of the composite seaweed carbon porous carrier are as follows: Modified thiosalicylic acid, methanol, and N,N-dimethylformamide were added to a reaction vessel and stirred for 30-40 minutes at 50-60℃ and 500-600 r / min. Then, a 10-12% (w / w) ammonia solution, ferric chloride hexahydrate, and seaweed carbon porous carrier were added, and the reaction was continued to be stirred for 20-22 hours. The mixture was filtered, and the filter cake was washed 2-4 times with deionized water and anhydrous ethanol, respectively. The mixture was then vacuum dried at 60-70℃ for 1-2 hours to obtain the composite seaweed carbon porous carrier.
[0018] Furthermore, the ratio of modified thiosalicylic acid, methanol, N,N-dimethylformamide, ammonia solution, ferric chloride hexahydrate, and seaweed carbon porous carrier is 70-72g: 200-220mL: 400-420mL: 120-140mL: 30-40g: 30-40g.
[0019] Furthermore, the specific preparation steps of the seaweed-based composite microcapsules are as follows: Sodium alginate and deionized water were added to a reaction vessel and stirred for 40-50 minutes at 20-25℃ and 500-600 rpm. Then, a live bacteria count of 1.0-1.2 × 10⁻⁶ was added. 8 Add CFU / mL of Bacillus subtilis culture and stir for 30-40 min to obtain a mixed solution. Add the mixed solution dropwise to a 3-4% calcium chloride solution, then add the composite seaweed carbon porous carrier and N,N'-dicyclohexylcarbodiimide. Continue stirring for 1-2 h, filter, wash the filter cake 2-4 times with deionized water and anhydrous ethanol respectively, and freeze-dry at -20℃ for 1-2 h to obtain seaweed-based composite microcapsules.
[0020] Furthermore, the ratio of sodium alginate, deionized water, and Bacillus subtilis bacterial solution is 60-62g: 800-900mL: 7-9mL.
[0021] Furthermore, the ratio of the mixed solution, calcium chloride solution, composite seaweed carbon porous carrier, and N,N'-dicyclohexylcarbodiimide is 70-80mL: 300-320mL: 50-52g: 2-4g.
[0022] The beneficial effects of this invention are as follows: 1. The seaweed-based composite water-soluble fertilizer prepared by this invention uses a composite seaweed char porous carrier to adsorb and fix gel microspheres containing Bacillus subtilis, giving it a good slow-release effect. Seaweed is a renewable marine biomass resource with wide availability and relatively low cost. Carbonizing it to prepare seaweed char realizes the resource utilization of marine biomass. At the same time, the introduction of Bacillus subtilis functional components and castor oil polyether polyol are both environmentally friendly substances, avoiding the soil residue risks caused by chemically synthesized additives.
[0023] 2. This invention forms a gel microsphere structure through the ionic cross-linking reaction of sodium alginate and calcium chloride, encapsulating Bacillus subtilis within it. Simultaneously, it is combined with a porous carrier of composite seaweed charcoal. This not only protects the live bacteria from damage caused by adverse factors in the soil and prolongs the survival time of the microorganisms, but also enables the slow release of nutrients through the porous structure, avoiding the problems of rapid nutrient loss and short fertilizer effect period of conventional water-soluble fertilizers.
[0024] 3. This invention uses the metal complex on the surface of the composite seaweed char porous carrier as a bridge to achieve effective bridging between the gel microspheres and the composite seaweed char porous carrier, thereby fixing the gel microspheres and preventing rapid loss. The porous structure of the composite seaweed char porous carrier and the metal complex loaded on its surface can reduce the heavy metal content in the soil.
[0025] 4. The seaweed-based compound water-soluble fertilizer of the present invention can achieve precise release. On the one hand, due to the water absorption and swelling effect of the gel microspheres, it can promote the release of Bacillus subtilis in the gel microspheres. On the other hand, the metal complex, which acts as a bridge, is pH responsive. In acidic soil, it can cooperate with the organic acids secreted by microorganisms in the soil to promote the collapse of the metal complex structure, so that the gel microspheres can be quickly detached and released. Detailed Implementation
[0026] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.
[0027] Example 1: A method for preparing a seaweed-based compound water-soluble fertilizer, comprising the following steps: S1: The seaweed is dried to make seaweed powder, which is then sieved to 100 mesh using a vibrating sieve and dried in a forced-air drying oven at 100℃ for 24 hours to obtain pretreated seaweed powder. The pretreated seaweed powder is placed in a reaction vessel, and nitrogen gas is introduced at a flow rate of 150 cm / min for 30 minutes. The mixture is then heated to 500℃ and kept at that temperature for 1 hour. After natural cooling, seaweed char is obtained.
[0028] S2: Add 200 mL of castor oil polyether polyol, 50 g of seaweed charcoal and 800 mL of N,N-dimethylformamide to a reaction vessel, and stir for 40 min at 20 °C and 500 r / min. Then add 0.5 g of triethylenediamine, 1 g of dibutyltin dilaurate, 0.4 mL of 1,4-butanediol and 200 mL of isocyanate, and continue stirring for 40 min. Pour into a mold, heat to 120 °C and stir at 80 r / min for 10 min, ripen, demold, cool naturally to room temperature, vacuum dry at 60 °C for 1 h, transfer to a muffle furnace, and calcine at 500 °C for 1 h under a nitrogen atmosphere to obtain a porous seaweed charcoal carrier.
[0029] S3: Add 80g of thiosalicylic acid and 500mL of deionized water to a reaction vessel and stir for 40min at 20℃ and 500r / min. Then add 40g of 2,5-diaminoterephthalic acid and continue stirring for 1h. Then add 15mL of 20% sulfuric acid solution to adjust the pH to 3, heat to 70℃, add 120mL of 37% formaldehyde solution dropwise, and continue the reaction for 4h. Filter under reduced pressure, wash the filter cake twice with deionized water and anhydrous ethanol, and dry it under vacuum at 60℃ for 1h to obtain modified thiosalicylic acid.
[0030] S4: Add 70g of modified thiosalicylic acid, 200mL of methanol and 400mL of N,N-dimethylformamide to a reaction vessel and stir for 30min at 50℃ and 500r / min. Then add 120mL of 10% ammonia solution, 30g of ferric chloride hexahydrate and 30g of seaweed carbon porous carrier. Continue stirring and react for 20h. Filter and wash the filter cake twice with deionized water and anhydrous ethanol, respectively. Dry under vacuum at 60℃ for 1h to obtain the composite seaweed carbon porous carrier.
[0031] S5: Add 60g sodium alginate and 800mL deionized water to the reactor and stir for 40min at 20℃ and 500r / min. Then add 7mL of Bacillus subtilis bacterial solution with a viable count of 1.0×10^8 CFU / mL and continue stirring for 30min to obtain a mixed solution. Add 70mL of the mixed solution dropwise to 300mL of 3% calcium chloride solution, then add 50g of composite seaweed carbon porous carrier and 2g of N,N'-dicyclohexylcarbodiimide and continue stirring for 1h. Filter and wash the filter cake twice with deionized water and anhydrous ethanol, respectively. Freeze-dry at -20℃ for 1h to obtain seaweed-based composite microcapsules.
[0032] S6: Add 50g of seaweed-based compound microcapsules, 10g of humic acid, 12g of urea and 3g of potassium sulfate to a mixer and mix evenly to obtain seaweed-based compound water-soluble fertilizer.
[0033] Example 2: A method for preparing a seaweed-based compound water-soluble fertilizer, comprising the following steps: S1: The seaweed is dried to make seaweed powder, which is then sieved to 110 mesh using a vibrating sieve and dried in a forced-air drying oven at 105℃ for 25 hours to obtain pretreated seaweed powder. The pretreated seaweed powder is placed in a reaction vessel, and nitrogen gas is introduced at a flow rate of 155 cm / min for 35 minutes. The mixture is then heated to 525℃ and kept at that temperature for 1.5 hours. After natural cooling, seaweed char is obtained.
[0034] S2: Add 250 mL of castor oil polyether polyol, 51 g of seaweed charcoal, and 850 mL of N,N-dimethylformamide to a reaction vessel and stir for 45 min at 22.5 °C and 550 r / min. Then add 0.65 g of triethylenediamine, 1.1 g of dibutyltin dilaurate, 0.45 mL of 1,4-butanediol, and 250 mL of isocyanate. Continue stirring for 45 min, pour into a mold, heat to 125 °C and stir at 85 r / min for 11 min, ripen, demold, cool naturally to room temperature, vacuum dry at 65 °C for 1.5 h, transfer to a muffle furnace, and calcine at 525 °C for 1.5 h under a nitrogen atmosphere to obtain a porous seaweed charcoal carrier.
[0035] S3: Add 85g of thiosalicylic acid and 550mL of deionized water to a reaction vessel and stir for 45min at 22.5℃ and 550r / min. Then add 45g of 2,5-diaminoterephthalic acid and continue stirring for 1.5h. Then add 16mL of 22.5% sulfuric acid solution to adjust the pH to 3.5, heat to 75℃, add 130mL of 37% formaldehyde solution dropwise, and continue the reaction for 4h. Filter under reduced pressure, wash the filter cake three times with deionized water and anhydrous ethanol respectively, and dry under vacuum at 65℃ for 1.5h to obtain modified thiosalicylic acid.
[0036] S4: 71g of modified thiosalicylic acid, 210mL of methanol and 410mL of N,N-dimethylformamide were added to a reaction vessel and stirred at 55℃ and 550r / min for 35min. Then, 130mL of 11% ammonia solution, 35g of ferric chloride hexahydrate and 35g of seaweed carbon porous support were added and the reaction was continued to be stirred for 21h. After filtration, the filter cake was washed three times with deionized water and anhydrous ethanol, respectively, and dried under vacuum at 65℃ for 1.5h to obtain the composite seaweed carbon porous support.
[0037] S5: Add 61g of sodium alginate and 850mL of deionized water to the reactor and stir for 45min at 22.5℃ and 550r / min. Then add 8mL of Bacillus subtilis bacterial solution with a viable count of 1.1×10^8 CFU / mL and continue stirring for 35min to obtain a mixed solution. Add 75mL of the mixed solution dropwise to 310mL of 3.5% calcium chloride solution, then add 51g of composite seaweed carbon porous carrier and 3g of N,N'-dicyclohexylcarbodiimide and continue stirring for 1.5h. Filter and wash the filter cake three times with deionized water and anhydrous ethanol, respectively. Freeze-dry at -20℃ for 1.5h to obtain seaweed-based composite microcapsules.
[0038] S6: Add 55g of seaweed-based compound microcapsules, 11g of humic acid, 13g of urea and 3.5g of potassium sulfate to a mixer and mix evenly to obtain seaweed-based compound water-soluble fertilizer.
[0039] Example 3: A method for preparing a seaweed-based compound water-soluble fertilizer, comprising the following steps: S1: The seaweed is dried to make seaweed powder, which is then sieved to 120 mesh using a vibrating sieve and dried in a forced-air drying oven at 110℃ for 26 hours to obtain pretreated seaweed powder. The pretreated seaweed powder is placed in a reaction vessel, and nitrogen gas is introduced at a flow rate of 160 cm / min for 40 minutes. The mixture is then heated to 550℃ and kept at that temperature for 2 hours. After natural cooling, seaweed char is obtained.
[0040] S2: Add 300 mL of castor oil polyether polyol, 52 g of seaweed charcoal and 900 mL of N,N-dimethylformamide to a reaction vessel, and stir for 50 min at 25 °C and 600 r / min. Then add 0.8 g of triethylenediamine, 1.2 g of dibutyltin dilaurate, 0.5 mL of 1,4-butanediol and 300 mL of isocyanate, and continue stirring for 50 min. Pour into a mold, heat to 130 °C and stir at 90 r / min for 12 min, ripen, demold, cool naturally to room temperature, vacuum dry at 70 °C for 2 h, transfer to a muffle furnace, and calcine at 550 °C for 2 h under a nitrogen atmosphere to obtain a porous seaweed charcoal carrier.
[0041] S3: Add 90g of thiosalicylic acid and 600mL of deionized water to a reaction vessel and stir for 50min at 25℃ and 600r / min. Then add 50g of 2,5-diaminoterephthalic acid and continue stirring for 2h. Then add 17mL of 25% sulfuric acid solution to adjust the pH to 4, heat to 80℃, add 140mL of 37% formaldehyde solution dropwise, and continue the reaction for 4h. Filter under reduced pressure, wash the filter cake four times with deionized water and anhydrous ethanol respectively, and dry under vacuum at 70℃ for 2h to obtain modified thiosalicylic acid.
[0042] S4: 72g of modified thiosalicylic acid, 220mL of methanol and 420mL of N,N-dimethylformamide were added to a reaction vessel and stirred at 60℃ and 600r / min for 40min. Then, 140mL of 12% ammonia solution, 40g of ferric chloride hexahydrate and 40g of seaweed carbon porous carrier were added and the reaction was continued to be stirred for 22h. After filtration, the filter cake was washed 4 times with deionized water and anhydrous ethanol, respectively, and dried under vacuum at 70℃ for 2h to obtain the composite seaweed carbon porous carrier.
[0043] S5: Add 62g of sodium alginate and 900mL of deionized water to the reactor and stir for 50min at 25℃ and 600r / min. Then add 9mL of Bacillus subtilis bacterial solution with a viable count of 1.2×10^8 CFU / mL and continue stirring for 40min to obtain a mixed solution. Add 80mL of the mixed solution dropwise to 320mL of 4% calcium chloride solution, then add 52g of composite seaweed carbon porous carrier and 4g of N,N'-dicyclohexylcarbodiimide and continue stirring for 2h. Filter and wash the filter cake four times with deionized water and anhydrous ethanol, respectively. Freeze-dry at -20℃ for 2h to obtain seaweed-based composite microcapsules.
[0044] S6: Add 60g of seaweed-based compound microcapsules, 12g of humic acid, 14g of urea and 4g of potassium sulfate to a mixer and mix evenly to obtain seaweed-based compound water-soluble fertilizer.
[0045] Comparative Example 1: Compared with Example 3, the porous alginate carbon carrier in step S4 was replaced with the porous alginate carbon carrier prepared in step S2.
[0046] Comparative Example 2: Compared with Example 3, the modified thiosalicylic acid in step S4 was omitted.
[0047] Comparative Example 3: Compared with Example 3, 2,5-diaminoterephthalic acid in step S3 was omitted.
[0048] In the examples and comparative examples: The Bacillus subtilis species in the Bacillus subtilis culture was Bacillus subtilis Y2, with accession number CGMCCNO.18752.
[0049] Thiosylsalicylic acid was purchased from Shanghai Maclean Biochemical Technology Co., Ltd., CAS No.: 147-93-3, molecular weight: 154.19.
[0050] Performance tests were conducted on the seaweed-based compound water-soluble fertilizers prepared in Examples 1-3 and Comparative Examples 1-3. The relevant performance tests were performed according to the national standard for slow-release fertilizers (GB / T23348-2009). The seaweed-based compound water-soluble fertilizers were soaked in still water at 25℃, and the nutrient release rates after 24 hours, 7 days, and 28 days were measured. Referring to the test methods in the "Soil Environmental Quality Standard," the fluoride content of different test soil samples was measured initially and after 3 months of application of different seaweed-based compound water-soluble fertilizers to evaluate the fertilizer's fluoride adsorption capacity. Referring to the test methods in the "Soil Environmental Quality Standard" (GB15618-2018), the arsenic content of different test soil samples was measured initially and after 6 months of application of different seaweed-based compound water-soluble fertilizers to evaluate the fertilizer's arsenic adsorption capacity. Referring to the test methods in "Soil Testing Part 4: Determination of Soil Bulk Density" (NY / T1121.4-2006), the bulk density of different test soil samples was tested.
[0051] Table 1 Performance Test Data of Seaweed-Based Compound Water-Soluble Fertilizer
[0052] As shown in Table 1, in Comparative Example 1, the gel microspheres failed to hold their fixation, and the slow-release nutrient properties were completely destroyed. The composite seaweed charcoal porous carrier, with its surface iron ions forming a metal complex with modified thiosalicylic acid, is the key fixation bridge for the gel microspheres. Without this bridge, the gel microspheres cannot stably bind to the porous carrier and are rapidly lost due to soil moisture erosion and microbial activity. The heavy metal adsorption capacity also decreased sharply. The metal complex is the core site for adsorbing fluorine and arsenic in the soil. Through coordination, heavy metal ions are chelated. Pure seaweed charcoal relies solely on porous physical adsorption, and its adsorption capacity and stability are far lower than chemical coordination adsorption. The gel microspheres absorb water and swell to fill the pores; the porous carrier provides skeletal support, which is crucial for reducing soil bulk density. In Comparative Example 1, the loss of gel microspheres indicates that pure seaweed charcoal alone cannot effectively improve the soil pore structure. The gel microspheres act as a barrier protecting Bacillus subtilis from damage by acids, alkalis, and enzymes in the soil. The rapid loss of gel microspheres exposes the live bacteria to an unfavorable environment, leading to the failure of functional microorganisms and further reducing fertilizer efficiency.
[0053] In Comparative Example 2, the metal complexes exhibited weak coordination ability and insufficient bridging effect, resulting in decreased heavy metal adsorption capacity and stability. The metal complexes formed by unmodified thiosalicylic acid had a loose structure, making them prone to dissociation after adsorbing heavy metals. Furthermore, the limited number of coordination sites led to low adsorption capacity, loss of pH responsiveness, and loss of precise release function. In acidic soils, the coordination structure was disrupted, causing the gel microspheres to detach and release nutrients. The removal of modified thiosalicylic acid resulted in nutrient release that could not adapt to the soil environment.
[0054] In Comparative Example 3, the modified thiosalicylic acid had functional group defects, resulting in a decrease in heavy metal adsorption capacity. The insufficient number of coordination sites led to a decrease in heavy metal adsorption capacity, but it still retained some coordination ability. The bridging effect disappeared, and it could not achieve precise response to soil acidity release.
[0055] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the invention.
Claims
1. A method for preparing a seaweed-based compound water-soluble fertilizer, characterized in that, Includes the following steps: Step 1: Dry and sieve the seaweed and then calcine it to prepare seaweed char; use seaweed char as a carrier, castor oil polyether polyol and isocyanate as raw materials, polymerize on the surface of seaweed char and then calcine to obtain a porous seaweed char carrier. Step 2: A hydroxymethyl intermediate is formed by the condensation of one end amino group of 2,5-diaminoterephthalic acid with formaldehyde. After protonation, an imine ion is generated. The imine ion attacks the carbon in the thiosalicylic acid structure to obtain modified thiosalicylic acid. The modified thiosalicylic acid undergoes a coordination reaction with the iron ions in ferric chloride to form a metal complex. Using a porous seaweed carbon carrier as a support, the metal complex is loaded into the pores to obtain a composite porous seaweed carbon carrier. Step 3: Sodium alginate and calcium chloride undergo a cross-linking reaction to form a gel network, which encapsulates Bacillus subtilis to form sodium alginate microcapsules. Then, after the remaining amino groups in the composite seaweed char porous carrier react with the carboxyl groups in the sodium alginate microcapsules, seaweed-based composite microcapsules are obtained. Step 4: Add seaweed-based composite microcapsules, humic acid, urea and potassium sulfate to a mixer and mix evenly to obtain seaweed-based composite water-soluble fertilizer; The mass ratio of the seaweed-based composite microcapsules, humic acid, urea, and potassium sulfate is 50-60:10-12:12-14:3-4.
2. The method for preparing a seaweed-based compound water-soluble fertilizer according to claim 1, characterized in that, The specific preparation steps for the seaweed charcoal are as follows: Seaweed is dried to make seaweed powder, which is then sieved to a fineness of 100-120 mesh using a vibrating sieve. The powder is then dried in a forced-air drying oven at 100-110℃ for 24-26 hours to obtain pretreated seaweed powder. The pretreated seaweed powder is placed in a reaction vessel, and nitrogen gas is introduced at a flow rate of 150-160 cm / min for 30-40 minutes. The mixture is then heated to 500-550℃ and held at that temperature for 1-2 hours. After natural cooling, seaweed char is obtained.
3. The method for preparing a seaweed-based compound water-soluble fertilizer according to claim 1, characterized in that, The specific preparation steps of the seaweed carbon porous carrier are as follows: Castor oil polyether polyol, seaweed charcoal, and N,N-dimethylformamide were added to a reaction vessel and stirred for 40-50 minutes at 20-25°C and 500-600 rpm. Then, triethylenediamine, dibutyltin dilaurate, 1,4-butanediol, and isocyanate were added, and stirring was continued for another 40-50 minutes. The mixture was then poured into a mold, heated to 120-130°C, and stirred at 80-90 rpm for 10-12 minutes to mature. After demolding, the mixture was allowed to cool naturally to room temperature and then vacuum dried at 60-70°C for 1-2 hours. Finally, it was transferred to a muffle furnace and calcined at 500-550°C for 1-2 hours under a nitrogen atmosphere to obtain a porous seaweed charcoal carrier.
4. The method for preparing a seaweed-based compound water-soluble fertilizer according to claim 3, characterized in that, The ratio of castor oil polyether polyol, seaweed charcoal, N,N-dimethylformamide, triethylenediamine, dibutyltin dilaurate, 1,4-butanediol, and isocyanate is 200-300mL: 50-52g: 800-900mL: 0.5-0.8g: 1-1.2g: 0.4-0.5mL: 200-300mL.
5. The method for preparing a seaweed-based compound water-soluble fertilizer according to claim 1, characterized in that, The specific preparation steps for the modified thiosalicylic acid are as follows: Thiosyl salicylic acid and deionized water were added to a reaction vessel and stirred for 40-50 min at 20-25℃ and 500-600 r / min. Then, 2,5-diaminoterephthalic acid was added and stirring was continued for 1-2 h. Then, 20-25% sulfuric acid solution was added to adjust the pH value to 3-4. The mixture was heated to 70-80℃, and 37% formaldehyde solution was added dropwise. The reaction was continued for 4 h. The mixture was then filtered under reduced pressure. The filter cake was washed 2-4 times with deionized water and anhydrous ethanol, respectively, and dried under vacuum at 60-70℃ for 1-2 h to obtain modified thiosalicylic acid.
6. The method for preparing a seaweed-based compound water-soluble fertilizer according to claim 5, characterized in that, The ratio of the amounts of thiosalicylic acid, deionized water, 2,5-diaminoterephthalic acid, sulfuric acid solution, and formaldehyde solution is 80-90g: 500-600mL: 40-50g: 15-17mL: 120-140mL.
7. The method for preparing a seaweed-based compound water-soluble fertilizer according to claim 1, characterized in that, The specific preparation steps of the composite seaweed carbon porous carrier are as follows: Modified thiosalicylic acid, methanol, and N,N-dimethylformamide were added to a reaction vessel and stirred for 30-40 minutes at 50-60℃ and 500-600 r / min. Then, a 10-12% (w / w) ammonia solution, ferric chloride hexahydrate, and seaweed carbon porous carrier were added, and the reaction was continued to be stirred for 20-22 hours. The mixture was filtered, and the filter cake was washed 2-4 times with deionized water and anhydrous ethanol, respectively. The mixture was then vacuum dried at 60-70℃ for 1-2 hours to obtain the composite seaweed carbon porous carrier.
8. The method for preparing a seaweed-based compound water-soluble fertilizer according to claim 7, characterized in that, The ratio of the modified thiosalicylic acid, methanol, N,N-dimethylformamide, ammonia solution, ferric chloride hexahydrate, and seaweed carbon porous carrier is 70-72g: 200-220mL: 400-420mL: 120-140mL: 30-40g: 30-40g.
9. The method for preparing a seaweed-based compound water-soluble fertilizer according to claim 1, characterized in that, The specific preparation steps of the seaweed-based composite microcapsules are as follows: Sodium alginate and deionized water were added to a reaction vessel and stirred for 40-50 minutes at 20-25℃ and 500-600 rpm. Then, a live bacteria count of 1.0-1.2 × 10⁻⁶ was added. 8 CFU / mL of Bacillus subtilis bacterial culture was stirred for 30-40 min to obtain a mixed solution. The mixed solution was added dropwise to a 3-4% calcium chloride solution, and then the composite seaweed carbon porous carrier and N,N'-dicyclohexylcarbodiimide were added. The mixture was stirred for 1-2 h, filtered, and the filter cake was washed 2-4 times with deionized water and anhydrous ethanol, respectively. The mixture was then freeze-dried at -20℃ for 1-2 h to obtain seaweed-based composite microcapsules. The ratio of sodium alginate, deionized water, and Bacillus subtilis culture is 60-62g: 800-900mL: 7-9mL; the ratio of mixed solution, calcium chloride solution, composite seaweed char porous carrier, and N,N'-dicyclohexylcarbodiimide is 70-80mL: 300-320mL: 50-52g: 2-4g.
10. A seaweed-based compound water-soluble fertilizer, characterized in that, It is prepared by the preparation method described in any one of claims 1-9.