Carbon-rich slow-release phosphorus fertilizer and preparation method thereof

Abstract

The present disclosure provides a kind of carbon-rich slow-release phosphorus fertilizer and its preparation method, which comprises: phosphorite powder is crushed, grinds and sieves;Straw and phosphorite powder are mixed with water to obtain a mixed reactant;The mixed reactant is subjected to co-hydrothermal reaction in a muffle furnace, and the suspension is obtained after cooling after reaction;The suspension is suction filtered, dried, to obtain a carbon-rich slow-release phosphorus fertilizer;Wherein, co-hydrothermal reaction makes the organic matter in straw and the inorganic components in phosphorite powder produce synergistic effect.The carbon fixation rate and carbon fixation potential of the carbon-rich slow-release phosphorus fertilizer prepared by the method provided by the present disclosure are improved, and it has a positive effect on soil and water conservation, fertilizer conservation, improvement of soil microstructure, improvement of organic carbon quality and promotion of carbon fixation.

Description

Technical Field

[0001] This disclosure relates to the fields of environmental technology and agricultural resource utilization, and more specifically, to the utilization of waste biomass and low-grade phosphate rock resources, and to the preparation of carbon-rich slow-release phosphate fertilizer by co-hydrothermal reaction of straw and phosphate rock powder. Background Technology

[0002] Straw is a type of waste biomass with a large output, but its utilization rate is relatively low. Straw has low energy density, high moisture content, and high manual processing costs. Large quantities of straw are discarded in the open or burned on-site, which not only wastes a lot of energy but also causes environmental pollution. Since crop residues are an unstable carbon source, directly returning straw to the field can cause soil acidification during biotransformation. Furthermore, once waste straw enters the soil as a carbon source, it is released into the atmosphere as greenhouse gases, damaging the ecological environment.

[0003] With the increasing severity of energy shortages and environmental pollution, agricultural environments are being polluted, hindering sustainable agricultural development and posing a threat to the ecological environment and human health. Therefore, the recycling and utilization of renewable waste biomass and the research and development of slow-release phosphate fertilizers are of great significance. Summary of the Invention

[0004] To address the aforementioned technical problems, this disclosure provides a carbon-rich slow-release phosphate fertilizer and its preparation method, aiming to at least partially solve the above-mentioned technical problems.

[0005] To solve the above-mentioned technical problems, the technical solution provided in this disclosure is as follows:

[0006] As one aspect of this disclosure, a method for preparing carbon-rich slow-release phosphate fertilizer is provided, comprising:

[0007] The phosphate rock powder is crushed, ground, and sieved.

[0008] Straw and phosphate rock powder are mixed with water to obtain a mixed reactant;

[0009] The mixed reactants were subjected to a co-hydrothermal reaction in a muffle furnace, and the suspension was obtained by cooling after the reaction.

[0010] The suspension was filtered and dried to obtain carbon-rich slow-release phosphate fertilizer.

[0011] Among them, the co-hydrothermal reaction enables the organic matter in the straw to have a synergistic effect with the inorganic components in the phosphate rock powder.

[0012] In one embodiment, this disclosure provides a method for preparing carbon-rich slow-release phosphate fertilizer, which further includes:

[0013] Before mixing straw and phosphate rock powder with water, wash, dry, crush, grind and sieve the straw.

[0014] The liquid obtained after filtration of the suspension is collected to obtain water-soluble phosphate fertilizer.

[0015] In one embodiment, the particle size of the straw and phosphate rock powder after grinding and sieving is less than 100 mesh.

[0016] In one embodiment, the mixing ratio of straw and phosphate rock powder is 1:5% to 1:10%; the solid-liquid ratio of straw and phosphate rock powder to water is 1:6 to 1:12.

[0017] In one embodiment, the co-hydrothermal reaction process includes: stirring the mixed reactants in a reaction vessel and agitating them until homogeneous;

[0018] The reactor was then locked and placed in a muffle furnace for a co-hydrothermal reaction.

[0019] In one embodiment, the duration of the co-hydrothermal reaction ranges from 4 to 16 hours.

[0020] In one embodiment, the temperature of the co-hydrothermal reaction ranges from 180 to 240°C; the heating rate of the co-hydrothermal reaction is 2°C / min.

[0021] In one embodiment, the pressure of the co-hydrothermal reaction includes 5 to 10 MPa.

[0022] In one embodiment, the vacuum filtration uses a filter membrane with a pore size of less than 0.45 μm.

[0023] Another aspect of this disclosure provides a carbon-rich slow-release phosphate fertilizer prepared by the above method.

[0024] Based on the above technical solution, this disclosure provides a carbon-rich slow-release phosphate fertilizer and its preparation method, which includes at least one of the following beneficial effects:

[0025] (1) By using the preparation method in this embodiment, waste biomass straw and phosphate rock powder are subjected to a hydrothermal reaction. The organic matter in the straw and the inorganic components in the phosphate rock powder have a strong synergistic effect, and the hydrothermal polymerization and aromatization reaction can recover the carbon in the straw and the phosphorus in the phosphate rock powder, so that the carbon-rich slow-release phosphate fertilizer has higher aroma and phosphorus content.

[0026] (2) In the embodiments of this disclosure, the co-hydrothermal reaction used to prepare carbon-rich slow-release phosphate fertilizer can generate organic small molecules in biomass straw during the hydrothermal process in a short time, which activates the insoluble phosphorus in phosphate rock powder and obtains carbon-rich slow-release phosphate fertilizer, providing a solution for the resource utilization of agricultural solid waste straw and phosphate rock.

[0027] (3) In the embodiments of this disclosure, waste straw and phosphate rock powder are reacted by co-hydrothermal reaction to obtain carbon-rich slow-release phosphate fertilizer. By adjusting different reaction conditions (such as reaction temperature, reaction time, reaction pressure, ratio of straw to phosphate rock powder, etc.), carbon-rich slow-release phosphate fertilizer with different stability can be prepared. This method has low energy consumption, no secondary pollution, simple and effective operation, and has high application prospects. Attached Figure Description

[0028] Figure 1 A schematic diagram of a method for preparing carbon-rich slow-release phosphate fertilizer using the method provided in this disclosure;

[0029] Figure 2 This is a comparison chart of the carbon fixation rate and carbon fixation potential of straw hydrothermal char and carbon-rich slow-release phosphate fertilizer at different reaction temperatures in the embodiments of this disclosure.

[0030] Figure 3 Thermogravimetric analysis diagrams of carbon-rich slow-release phosphate fertilizer and straw prepared at different reaction temperatures in the embodiments of this disclosure;

[0031] Figure 4 Thermogravimetric analysis diagrams of carbon-rich slow-release phosphate fertilizer and straw prepared at different reaction times in the embodiments of this disclosure;

[0032] Figure 5 Fourier transform infrared spectra of straw, phosphate rock powder, and carbon-rich slow-release phosphate fertilizer at different reaction temperatures in the embodiments of this disclosure.

[0033] Figure 6 X-ray diffraction patterns of straw, phosphate rock powder, and carbon-rich slow-release phosphate fertilizers prepared at different reaction temperatures in the embodiments of this disclosure;

[0034] Figure 7 X-ray diffraction patterns of straw, phosphate rock powder, and carbon-rich slow-release phosphate fertilizers prepared at different reaction times in the embodiments of this disclosure;

[0035] Figure 8 This is a graph showing the phosphorus content of different components of straw, straw hydrothermal charcoal, and carbon-rich slow-release phosphate fertilizer in the embodiments of this disclosure;

[0036] Figure 9 The graph shows the sulfur, iron, aluminum, calcium, and potassium content of straw hydrothermal char and carbon-rich slow-release phosphate fertilizer at different reaction temperatures in the embodiments of this disclosure. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of this disclosure clearer, the following detailed description is provided in conjunction with specific embodiments and the accompanying drawings.

[0038] In the process of realizing this disclosure, it was discovered that hydrothermal carbonization technology can recover nutrients from waste biomass. This technology simulates the natural coalification process, converting biomass into hydrothermal carbon with high active carbon content, soluble organic components, and oxygen-containing functional groups in a relatively short time, thereby recovering nutrients from the waste biomass. However, the product obtained by directly hydrothermally processing waste straw has a low nutrient content and is not suitable for direct application as fertilizer.

[0039] In the process of developing this disclosure, it was discovered that phosphorus is an essential nutrient element for crop growth, and the application of phosphate fertilizers can ensure crop yields. However, most phosphate fertilizers on the market are derived from the mining of phosphate rock resources, but phosphate rock reserves are limited and non-renewable, making usable phosphate rock resources increasingly scarce. Currently, 80% of the phosphate fertilizers on the market are fast-acting water-soluble phosphate fertilizers. These fertilizers require high-grade phosphate rock powder as raw material, and after application, they are rapidly absorbed by minerals in the soil, resulting in large amounts of loss and easily leading to eutrophication and water pollution.

[0040] Therefore, in the process of realizing this disclosure, it was discovered that developing new technologies to recycle waste straw and conducting research and development on the preparation of slow-release phosphorus fertilizers using low-grade phosphate rock powder as raw material can alleviate environmental pollution and increase agricultural income, which has important economic and social significance.

[0041] The technical problem this disclosure aims to solve is to provide a simple, low-cost, and environmentally friendly method for preparing carbon-rich slow-release phosphate fertilizer, thereby improving the carbon fixation rate and yield of phosphate fertilizer and obtaining a carbon-rich slow-release phosphate fertilizer rich in organic activated carbon and inorganic nutrients. Specifically, this disclosure provides a method for preparing carbon-rich slow-release phosphate fertilizer using a co-hydrothermal reaction of waste straw and phosphate rock powder. The resulting phosphate fertilizer has a high content of activated carbon, abundant soluble organic components, rich oxygen-containing functional groups, and high phosphorus nutrient content, which can reduce greenhouse gas emissions while providing organic matter and inorganic nutrients to the soil. Furthermore, the carbon-rich slow-release phosphate fertilizer provided by this disclosure is slightly acidic, which can lower the pH of saline-alkali soils and increase salt precipitation, making it more advantageous in improving low-yield saline-alkali soils. This method is simple to operate, and the resulting phosphate fertilizer has high carbon fixation potential, showing promise for large-scale production.

[0042] According to embodiments of this disclosure, this disclosure provides a method for preparing carbon-rich slow-release phosphate fertilizer, comprising:

[0043] The phosphate rock powder is crushed, ground, and sieved.

[0044] Straw and phosphate rock powder are mixed with water to obtain a mixed reactant;

[0045] The mixed reactants were subjected to a co-hydrothermal reaction in a muffle furnace, and the suspension was obtained by cooling after the reaction.

[0046] The suspension was filtered and dried to obtain carbon-rich slow-release phosphate fertilizer.

[0047] Among them, the co-hydrothermal reaction enables the organic matter in the straw to have a synergistic effect with the inorganic components in the phosphate rock powder.

[0048] In this embodiment, the phosphate rock powder can be selected as low-grade phosphate rock powder, and the straw includes at least one of corn straw, rice straw, wheat straw, potato straw, and cotton straw, but is not limited to these categories. The preparation of carbon-rich slow-release phosphate fertilizer by co-hydrothermal reaction of waste straw with low-grade phosphate rock powder achieves the recycling of waste biomass and the resource utilization of low-grade phosphate rock powder.

[0049] In the embodiments of this disclosure, the method for preparing carbon-rich slow-release phosphate fertilizer provided by this disclosure can recover nutrients from waste biomass through a co-hydrothermal reaction and activate phosphate rock powder to generate a substance with a carbon apatite-like structure. This results in a carbon-rich slow-release phosphate fertilizer with low crystallinity, rich in organic active carbon and inorganic nutrient components, and higher bioavailability, thus avoiding the problems of insufficient mineral nutrient content and low carbon fixation rate of traditional straw hydrothermal carbon.

[0050] According to embodiments of this disclosure, before mixing straw and phosphate rock powder with water, the straw is washed, dried, crushed, ground, and sieved.

[0051] The liquid obtained after filtration of the suspension is collected to obtain water-soluble phosphate fertilizer.

[0052] In the embodiments of this disclosure, low-grade phosphate rock powder is "dissolved" into water-soluble phosphorus in the liquid phase by organic acid substances generated from straw during the hydrothermal reaction process, which can yield a liquid product, namely water-soluble phosphate fertilizer obtained after filtration. It can also be used in the soil to quickly provide phosphorus nutrients to the soil.

[0053] Figure 1 The following is a schematic diagram of the method for preparing carbon-rich slow-release phosphate fertilizer using the method provided in this disclosure. Figure 1 The method for preparing carbon-rich slow-release phosphate fertilizer disclosed herein is described in detail.

[0054] Specifically, such as Figure 1As shown, in preparing carbon-rich slow-release phosphate fertilizer, straw is washed, dried, crushed using a wall-breaking machine, and ground and sieved to obtain straw powder. Low-grade phosphate rock powder is then crushed, ground, and sieved. Subsequently, the ground and sieved straw and low-grade phosphate rock powder are mixed with a certain proportion of water to obtain a mixed reactant. The reaction temperature is adjusted to 180–240℃ for a co-hydrothermal reaction, which is carried out for 4–16 hours. After a period of reaction, the mixture is cooled to room temperature and vacuum filtered to obtain carbon-rich slow-release phosphate fertilizer. The filtered liquid can also yield water-soluble phosphate fertilizer. The method for preparing carbon-rich slow-release phosphate fertilizer provided in this disclosure can convert straw into hydrothermal carbon with high active carbon content, abundant soluble organic components, and rich oxygen-containing functional groups in a short time through a co-hydrothermal reaction. This allows for strong interaction between straw and phosphate rock powder under hydrothermal conditions, significantly increasing the yield of carbon-rich slow-release phosphate fertilizer. This method plays a positive role in soil and water conservation, fertilizer retention, improving soil microstructure, increasing soil organic carbon quality, and promoting soil carbon sequestration.

[0055] According to embodiments of this disclosure, the particle size of the straw and phosphate rock powder after grinding and sieving is less than 100 mesh, wherein the corn straw and phosphate rock powder are both passed through a 100-mesh sieve after being crushed and ground.

[0056] According to embodiments of this disclosure, the mixing ratio of straw and phosphate rock powder includes 1:5% to 1:10%, wherein 1:5%, 1:6%, 1:8%, 1:10%, etc. are optional.

[0057] According to embodiments of this disclosure, the solid-liquid ratio of straw and phosphate rock powder to water includes 1:6 to 1:12, and can be selected as 1:6, 1:8, 1:10, 1:12, etc. Specifically, when the solid-liquid ratio is lower than 1:6, the polymerization reaction will start earlier at a lower water / biomass ratio, inhibiting further thermal conversion of biochar; when the solid-liquid ratio is higher than 1:12, the yield of carbon-rich slow-release phosphate fertilizer obtained at a higher water / biomass ratio is lower. Therefore, in the embodiments of this disclosure, it is not advisable to add too much water during the preparation of carbon-rich slow-release phosphate fertilizer using the method provided in this disclosure. Preferably, the solid-liquid ratio of straw and phosphate rock powder to water is 1:10.

[0058] According to embodiments of this disclosure, the co-hydrothermal reaction process includes: stirring the mixed reactants in a reaction vessel and agitating them until homogeneous; then locking the reaction vessel and placing it in a muffle furnace for co-hydrothermal reaction.

[0059] In the embodiments of this disclosure, corn stalks and phosphate rock powder are mixed with water in a polytetrafluoroethylene liner, stirred and shaken to ensure uniformity (or uniform mixing can be performed without a liner), and then the liner containing the mixture is locked in a stainless steel reactor and placed in a muffle furnace for a co-hydrothermal reaction.

[0060] According to embodiments of this disclosure, the duration of the hydrothermal reaction ranges from 4 to 16 hours. Selective durations include 4 hours, 6 hours, 8 hours, 10 hours, 12 hours, 14 hours, and 16 hours. After 4 hours of hydrothermal reaction, hemicellulose and cellulose are essentially hydrolyzed. At 16 hours, the straw begins to form hydrothermal carbon microspheres, and amorphous cellulose and some soluble fragments of lignin are also uniformly hydrolyzed. The hydrolysis products subsequently re-aggregate to form microspheres. Therefore, selecting a reaction duration of 4 to 16 hours allows the straw and phosphate rock powder to fully react and generate carbon-rich slow-release phosphate fertilizer.

[0061] According to embodiments of this disclosure, the temperature of the co-hydrothermal reaction ranges from 180 to 240°C; the heating rate of the co-hydrothermal reaction is 2°C / min. The reaction temperature can be selected from 180°C, 200°C, 220°C, 240°C, etc. Since straw is a lignocellulose biomass, the hemicellulose and cellulose components can decompose at a hydrothermal temperature of 180°C, while the decomposition temperature of the lignin component is higher than 240°C. Therefore, within this hydrothermal temperature range, the straw and phosphate rock powder can fully react to generate a carbon-rich slow-release phosphate fertilizer with abundant oxygen-containing functional groups and a high phosphorus content.

[0062] In the embodiments disclosed herein, reaction temperature and reaction time are key factors affecting the recovery of carbon from straw and phosphorus from phosphate rock powder. The reaction temperature and reaction time of the mixture can not only affect the hydrothermal dehydration and decarboxylation process of the reactants in the co-hydrothermal reaction to improve the aromaticity of hydrothermal carbon, but also affect the distribution and characteristics of gas-liquid-solid products. Therefore, the parameter adjustment operation of the hydrothermal reaction needs to be strictly controlled.

[0063] According to embodiments of this disclosure, the pressure of the co-hydrothermal reaction includes 5 to 10 MPa. The reaction pressure can be selected from 5 MPa, 6 MPa, 8 MPa, 10 MPa, etc. The preferred pressure for the co-hydrothermal reaction is 8 MPa. When the reaction pressure is less than 5 MPa, the reaction will be incomplete, while when the reaction pressure is greater than 10 MPa, the excessive pressure will result in a low yield of carbon-rich slow-release phosphate fertilizer.

[0064] According to embodiments of this disclosure, the vacuum filtration uses a filter membrane with a pore size of 0.45 μm or less.

[0065] According to embodiments of this disclosure, a carbon-rich slow-release phosphate fertilizer prepared by the above method is provided. Further, the obtained carbon-rich slow-release phosphate fertilizer is subjected to thermogravimetric analysis, X-ray diffraction, Fourier transform infrared spectroscopy, and other tests and analyses. The ash content is analyzed by determining the C, H, N, and S elemental contents using an elemental analyzer, and the Ca, Al, Fe, K, and P elements in the carbon-rich slow-release phosphate fertilizer are determined by inductively coupled plasma optical emission spectroscopy (ICP-OES).

[0066] In the embodiments of this disclosure, corn stalks are washed and dried at 60°C. The corn stalks and phosphate rock powder are then crushed separately using a high-speed blender and ground through a 100-mesh sieve. The corn stalks and phosphate rock powder (in a ratio of 1:5%) are mixed with water at an optimal solid-liquid ratio of 1:10 in a polytetrafluoroethylene liner and stirred and shaken until homogeneous. The liner containing the mixture is then locked in a stainless steel reactor and placed in a muffle furnace. The temperature is increased to 220°C at a rate of 2°C / min, and the pressure is set to 8MPa. After reacting in the muffle furnace for 16 hours, the mixture is cooled to room temperature and removed to obtain a suspension. The suspension is then vacuum filtered through a 0.45μm filter membrane and dried in a vacuum freeze dryer for 24 hours to obtain the final product, carbon-rich slow-release phosphate fertilizer. The filtered liquid is collected to obtain water-soluble phosphate fertilizer. The prepared carbon-rich slow-release phosphate fertilizer has a carbon fixation rate of up to 69.6% and a carbon fixation potential of 43.1%; the total phosphorus content is 8.0 g / kg, the inorganic phosphorus content of apatite is 5.4 g / kg, and the inorganic phosphorus content of non-apatite is 0.6 g / kg.

[0067] To make the objectives, technical solutions, and advantages of this disclosure clearer, the technical solutions and principles of this disclosure are further illustrated below with reference to specific embodiments and accompanying drawings. It should be noted that the specific embodiments described below are merely illustrative examples, and the scope of protection of this disclosure is not limited thereto.

[0068] Unless otherwise specified, all test materials and reagents used in the following examples are commercially available.

[0069] Unless otherwise specified in the embodiments, all methods are conventional and can be performed in accordance with the techniques or conditions described in the literature in this field or in accordance with the product manual.

[0070] Example 1

[0071] Corn stalks were washed with deionized water and dried at 60℃ for 48 hours. They were then ground and sieved through a 100-mesh sieve. 2g of corn stalks were weighed and placed in a 50mL PTFE liner, along with 20mL of deionized water. The liner was then sealed and placed in a stainless steel autoclave. The autoclave was placed in a muffle furnace, and the programmed heating rate was set to 2℃ / min, the reaction temperature to 180℃, the reaction pressure to 8MPa, and the residence time to 16 hours for a co-hydrothermal reaction. After the reaction, the autoclave was allowed to cool to room temperature naturally with air. The resulting solid-liquid mixture was then vacuum filtered through a 0.45μm filter membrane and subsequently freeze-dried in a vacuum freeze dryer for 24 hours to obtain hydrothermal charcoal from the corn stalks.

[0072] In Example 1 of this disclosure, while keeping other reaction conditions unchanged, experiments were conducted by changing the reaction temperature to 200°C, 220°C, and 240°C.

[0073] Figure 2 This is a comparison chart of the carbon fixation rate and carbon fixation potential of straw hydrothermal char and carbon-rich slow-release phosphate fertilizer at different reaction temperatures in the embodiments of this disclosure. The carbon fixation rate refers to the ability of the carbon-rich slow-release phosphate fertilizer to fix carbon in the raw materials during the hydrothermal process, while the carbon fixation potential refers to the significant long-term sequestration potential of the carbon-rich slow-release phosphate fertilizer in the soil due to its stability.

[0074] Depend on Figure 2 It can be seen that the hydrothermal reaction of straw at different temperatures, with the straw hydrothermal char obtained at 220℃ and 240℃ having higher carbon fixation potential and relatively higher carbon fixation rate.

[0075] Example 2

[0076] Corn stalks were washed with water, dried at 60℃ for 48 hours, and then pulverized using a grinder. Low-grade phosphate rock powder was ground and sieved. Both corn stalks and phosphate rock powder were ground and sieved through a 100-mesh sieve. With a mixing ratio of 1:5% for stalks and 1:10 for water, 2g of sieved corn stalks and 0.1g of phosphate rock powder were weighed and placed into a 50mL polytetrafluoroethylene (PTFE) liner of a reactor. 20mL of water was added and the mixture was stirred and vibrated until homogeneous. The lid was then closed, and the liner containing the reaction mixture was secured with a stainless steel reactor. The high-pressure reactor was placed in a muffle furnace, and the temperature was increased at a rate of 2℃ / min until the reaction temperature reached 180℃. The reaction pressure was set to 8MPa, and the reactor was held in a hydrothermal environment for 16 hours. After the reaction, the high-pressure reactor was allowed to cool to room temperature naturally with air. The suspension after reaction was filtered under vacuum through a 0.45 μm filter membrane to obtain a solid product, which was then freeze-dried in a vacuum freeze dryer for 24 h to obtain a carbon-rich slow-release phosphate fertilizer.

[0077] In Example 2 of this disclosure, while keeping other reaction conditions unchanged, experiments were conducted by changing the reaction temperature to 200°C, 220°C, and 240°C.

[0078] Depend on Figure 2 It can be seen that, at the same temperature, the carbon-rich slow-release phosphate fertilizer prepared by the method provided in this disclosure has a higher carbon fixation rate and carbon fixation potential than straw hydrothermal char. The carbon-rich slow-release phosphate fertilizer prepared under the conditions of reaction temperature of 220℃ and residence time of 16h can achieve a carbon fixation rate of 69.6% and a carbon fixation potential of 43.1%.

[0079] Example 3

[0080] The same preparation method as in Example 2 was used, the only difference being that the reaction temperature in Example 2 was 220°C and the reaction time was 1 hour.

[0081] Example 4

[0082] The same preparation method as in Example 2 was used, the only difference being that the reaction temperature in Example 2 was 220°C and the reaction time was 4 hours.

[0083] The straw and the carbon-rich slow-release phosphate fertilizer prepared by the above method were passed through a 200-mesh sieve and weighed 5 ± 0.1 mg. Thermogravimetric analysis (TGA, NETZSCH TG 209) was performed in a temperature range from ambient to 800 °C at a heating rate of 10 °C / min and a gas flow rate of 60 mL / min (N2:O2 = 4:1) to assess stability.

[0084] Figure 3 The thermogravimetric analysis (TGA) charts of carbon-rich slow-release phosphate fertilizer and straw prepared at different reaction temperatures in the embodiments of this disclosure are shown. Figure 3 As shown, the carbon-rich slow-release phosphate fertilizer prepared using the preparation method provided in this disclosure exhibits high stability at reaction temperatures of 220℃ and 240℃ when the co-hydrothermal reaction time is 16h.

[0085] Figure 4 Thermogravimetric analysis (TGA) diagrams of carbon-rich slow-release phosphate fertilizer and straw prepared at different reaction times in the embodiments of this disclosure are shown. Figure 4 It can be seen that when the hydrothermal reaction temperature is 220℃, the reaction time affects the thermal stability. Under the condition of a reaction time of 16h, both straw hydrothermal charcoal and carbon-rich slow-release phosphate fertilizer showed good stability.

[0086] Depend on Figure 3 and Figure 4 It is evident that carbon-rich slow-release phosphate fertilizer exhibits lower volatility and combustion temperature compared to straw and straw hydrothermal char, demonstrating higher thermal stability. Combined with... Figure 2 It can be concluded that the carbon-rich slow-release phosphate fertilizer prepared under the conditions of reaction temperature of 220℃ and reaction time of 16h has good application prospects in carbon sequestration and emission reduction.

[0087] Furthermore, Fourier transform infrared spectroscopy (FT-IR, Spectrum 400, PerkinElmer) was used to analyze the surface functional groups of straw, phosphate rock powder, and carbon-enriched slow-release phosphate fertilizer. X-ray diffraction (XRD, Bruker Advance D8 diffractometer) was used to analyze the crystal structure of straw, phosphate rock powder, and carbon-enriched slow-release phosphate fertilizer.

[0088] Figure 5 These are Fourier transform infrared (FTIR) spectra of straw, phosphate rock powder, and carbon-rich slow-release phosphate fertilizer at different reaction temperatures in the embodiments of this disclosure. Figure 5It can be observed that the carbon-enriched slow-release phosphate fertilizer prepared by the method disclosed herein has more oxygen-containing and aromatic functional groups compared with straw and straw hydrothermal char, resulting in a higher content of soluble organic matter and a stable organic carbon source. Furthermore, the phosphorus in the carbon-enriched slow-release phosphate fertilizer is an activated phosphorus mineral. Therefore, the carbon-enriched slow-release phosphate fertilizer can rapidly replenish soil organic matter while also possessing a certain degree of stability.

[0089] Figure 6 X-ray diffraction patterns of straw, phosphate rock powder, and carbon-rich slow-release phosphate fertilizers prepared at different reaction temperatures in the embodiments of this disclosure; Figure 7 The X-ray diffraction patterns are shown for straw, phosphate rock powder, and carbon-rich slow-release phosphate fertilizers prepared at different reaction times in the embodiments of this disclosure.

[0090] from Figure 6 and Figure 7 It is evident that the carbon-rich slow-release phosphate fertilizer prepared using the method provided in this disclosure at 220℃ and 240℃ exhibits lower crystallinity compared to straw and straw hydrothermal char. The carbon-rich slow-release phosphate fertilizer has a lower crystal structure and a higher content of active amorphous material. Increasing the reaction temperature and reaction time can reduce its crystallinity, increase its disorder, and increase its amorphous content. Figure 5 Analysis shows that carbon-rich slow-release phosphate fertilizer has better phosphorus slow-release characteristics, which is conducive to improving the utilization rate of phosphate rock resources. It can easily release nutrients in the soil and provide rich nutrients to the soil.

[0091] In addition, the contents of total phosphorus, inorganic phosphorus, organic phosphorus, inorganic phosphorus from apatite, and inorganic phosphorus from non-apatite in the carbon-enriched slow-release phosphate fertilizer were determined using standard measurement and testing methods. Phosphorus concentration was determined by ICP-OES after extraction. The contents of Ca, Al, K, and Fe in straw hydrothermal charcoal and carbon-enriched slow-release phosphate fertilizer were also determined by ICP-OES.

[0092] Figure 8 This is a graph showing the phosphorus content of different components of straw, straw hydrothermal charcoal, and carbon-rich slow-release phosphate fertilizer in the embodiments of this disclosure.

[0093] Depend on Figure 8 It can be seen that the total phosphorus content of the carbon-rich slow-release phosphate fertilizer prepared at a reaction temperature of 220℃ and a reaction time of 16 hours is 8.0 g / kg, the inorganic phosphorus content of apatite is 5.4 g / kg, and the inorganic phosphorus content of non-apatite is 0.6 g / kg. The inorganic phosphorus from apatite can be absorbed by plants, exhibiting high bioavailability and providing the soil with more organic matter and inorganic nutrients.

[0094] Figure 9 The graph shows the sulfur, iron, aluminum, calcium, and potassium content of straw hydrothermal char and carbon-rich slow-release phosphate fertilizer at different reaction temperatures in the embodiments of this disclosure.

[0095] Depend on Figure 9It can be seen that carbon-rich slow-release phosphate fertilizer contains large amounts of Ca, Al, Fe, and K elements. Inorganic phosphorus is divided into apatite inorganic phosphorus bound to calcium, and non-apatite inorganic phosphorus bound to aluminum and iron. Under higher temperatures and longer reaction times, phosphorus bound to Fe and Al is converted into phosphorus bound to Ca. Figure 8 It can be observed that the phosphorus bound to calcium in the carbon-rich slow-release phosphate fertilizer mainly exists as inorganic phosphorus in hydroxyapatite, which can gradually release phosphorus. In addition, the humic substances formed by straw during the hydrothermal process can also inhibit the fixation of water-soluble phosphate fertilizer in the soil while promoting the slow release of phosphorus from the carbon-rich slow-release phosphate fertilizer in the soil. Therefore, the carbon-rich slow-release phosphate fertilizer prepared by reacting straw and phosphate rock powder at a reaction temperature of 220℃ and a residence time of 16h has higher nutritional characteristics.

[0096] The specific embodiments described above further illustrate the purpose, technical solutions, and beneficial effects of this disclosure. It should be understood that the above descriptions are merely specific embodiments of this disclosure and are not intended to limit this disclosure. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this disclosure should be included within the protection scope of this disclosure.

Claims

1. A method for preparing a carbon-rich slow-release phosphate fertilizer, comprising: The phosphate rock powder is crushed, ground, and sieved. The straw and the phosphate rock powder were mixed with water to obtain a mixed reactant. The mixed reactants were subjected to a co-hydrothermal reaction in a muffle furnace, and the mixture was cooled after the reaction to obtain a suspension. The suspension was filtered and dried to obtain carbon-rich slow-release phosphate fertilizer. The solid-liquid ratio of the straw and phosphate rock powder to water is 1:6 to 1:

12. The co-hydrothermal reaction causes the organic matter in the straw and the inorganic components in the phosphate rock powder to have a synergistic effect, forming a carbon-rich slow-release phosphate fertilizer with aromaticity and a carbon apatite-like structure.

2. The method according to claim 1, further comprising: Before mixing the straw and phosphate rock powder with water, the straw is washed, dried, crushed, ground, and sieved. The liquid obtained after filtration of the suspension is collected to obtain water-soluble phosphate fertilizer.

3. The method according to claim 2, wherein, The straw and phosphate rock powder, after being ground and sieved, have a particle size of less than 100 mesh.

4. The method according to claim 1, wherein, The mixing ratio of straw and phosphate rock powder is 1:5% to 1:10%.

5. The method according to claim 1, wherein, The hydrothermal reaction process includes: The mixed reactants are stirred and vibrated until homogeneous in the reaction vessel; The reactor is then locked and placed in the muffle furnace for a co-hydrothermal reaction.

6. The method according to claim 1, wherein, The duration of the co-hydrothermal reaction ranges from 4 to 16 hours.

7. The method according to claim 1, wherein, The temperature range for the co-hydrothermal reaction is 180~240℃; The heating rate of the co-hydrothermal reaction is 2℃ / min.

8. The method according to claim 1, wherein, The pressure of the co-hydrothermal reaction includes 5~10 MPa.

9. The method according to claim 1, wherein, The filtration process uses a filter membrane with a pore size of less than 0.45 μm.

10. A carbon-rich slow-release phosphate fertilizer, wherein the carbon-rich slow-release phosphate fertilizer is prepared by the method described in any one of claims 1-9.

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