Composite carbon-based slow-release fertilizer prepared by synergistic modification of coal water slurry gasification slag and biomass as well as preparation method and application of composite carbon-based slow-release fertilizer

Abstract

The invention provides a method for preparing a composite carbon-based slow-release fertilizer by synergistic modification of coal water slurry gasification slag and biomass, which comprises the following steps: step S1, crushing coal water slurry gasification slag, mixing with a chlorinating agent according to a certain mass ratio, reacting for a period of time at a certain temperature in a chlorine-containing gas atmosphere, filtering, and drying to obtain the composite carbon-based slow-release fertilizer. Removing heavy metals, washing with water, and drying to obtain detoxified gasified slag; s2, mixing the detoxified gasification slag with biomass powder, and roasting; s3, the roasted product is crushed after being subjected to acid pickling and functional additive strengthening, and the composite carbon-based fertilizer is obtained; the Pb / Cd / As residue of the fertilizer is less than or equal to 5ppm, namely the removal rate is greater than or equal to 96%, the specific surface area is 280-350m < 2 > / g, the hierarchical pore size distribution is realized,-OH is greater than or equal to 1.2 mmol / g, and-COOH is greater than or equal to 1.8 mmol / g; the 28d nitrogen and phosphorus accumulative release rate is less than or equal to 25%, the soil water retention rate is increased by more than or equal to 25%, the heavy metal exchange state is reduced by more than or equal to 60%, the preparation cost is about 780-820 yuan / t, the process is simple and controllable, and remarkable environmental protection and economic benefits are achieved.

Description

Technical Field

[0001] The present invention relates to the field of industrial solid waste resource utilization and environmental protection technology, and in particular to a composite carbon-based slow-release fertilizer prepared by synergistic modification of water-coal slurry gasification slag and biomass, a preparation method and applications thereof. Background Art

[0002] In recent years, although biochar-based slow-release fertilizer technology has made certain progress, it still faces multiple technical bottlenecks, especially in the coordinated utilization of industrial solid waste and functional complexity.

[0003] Traditional detoxification processes destroy the carbon structure. For example, patent CN112125512A uses sulfuric acid leaching to treat gasification slag. Although the removal rate can reach 85%, strong acid corrosion causes the carbon skeleton to collapse, the porosity drops to below 40%, and the biomass resource utilization is not integrated. Similarly, patent CN11990787A uses hydrochloric acid to treat the straw surface for high-temperature carbonization, resulting in loss of active ingredients: patent CN113480357A relies on high-temperature carbonization of biomass at 600°C, resulting in a humic acid content of only 8%, and no heavy metal detoxification step is introduced. The As residual content reaches 10ppm (5 times the standard). Patent CN13495415A uses biomass charcoal to wrap urea. Although it achieves a slow-release function, the carbonization temperature exceeds 500°C, which still causes a thermal decomposition loss of humic acid of >70%.

[0004] There are also issues of reliance on exogenous sustained-release agents and cost. For example, patent CN117736041A uses exogenous coating materials such as betaine and citric acid to achieve sustained release. While this controlled-release effect is significant, it increases costs by 25%. Furthermore, the coating material is not biodegradable enough, posing a risk of soil contamination. Furthermore, patent CN17332348A uses a composite carbon-based formula (such as potassium citrate and seaweed powder), which improves fertilizer efficiency but does not utilize industrial solid waste, resulting in high raw material costs.

[0005] The synergistic utilization of solid waste is insufficient. For example, patent CN43197024A utilizes the residual charcoal from the gasification of construction waste to produce organic fertilizer. While this achieves resource utilization, it does not address the issue of heavy metal detoxification. Furthermore, the high alkalinity requires adjustment with acidic tail liquid, increasing the complexity of the process. Patent CN15498436A, while improving water retention by combining biochar with a highly absorbent resin, does not address the synergistic treatment of industrial solid wastes such as gasification slag, limiting its scope of application.

[0006] Functional singularity and environmental risks: Existing technologies often focus on a single function (such as slow-release or water retention). For example, patent CN114478132A combines biochar with fungicides for disease control, but fails to optimize the synergy between humic acid activity and nutrient slow-release. Patent CN12788291A achieves long-term slow-release through carbon-based fertilizer rods, but relies on chemical binders, potentially introducing secondary pollution. [The text then abruptly shifts topics:] ...

[0007] In summary, although existing biochar-based slow-release fertilizers have made certain progress in detoxification, nutrient slow-release and water retention, they generally have bottlenecks such as carbon skeleton destruction, single function, high cost and insufficient coordinated utilization of industrial solid waste. There is an urgent need for an innovative synergistic modification technology solution that takes into account efficient detoxification, structural and functional co-protection, controllable cost and the deep integration of gasification slag and biomass resources. Summary of the Invention

[0008] The present invention innovatively integrates three major technologies: chlorination gradient detoxification, hydrothermal / pyrolysis synergistic modification, and functional microbial compounding. It not only achieves the performance indicators of heavy metal removal rate ≥96% of water-coal slurry gasification slag, humic acid activity ≥15%, and 28-day nitrogen and phosphorus cumulative sustained release rate ≤25%, but also constructs a multi-level pore structure and high-density -OH / -COOH functional groups, providing a new solution for nutrient sustained release, soil improvement, and heavy metal solidification. The entire process is low-cost and controllable, with diversified raw materials, and has significant industrial promotion value and ecological and environmental benefits.

[0009] Specifically, the present invention is a method for preparing a composite carbon-based slow-release fertilizer by synergistic modification of coal-water slurry gasification slag and biomass, comprising the following steps:

[0010] Step S1, crushing the water-coal slurry gasification slag and mixing it with a chlorinating agent in a certain mass ratio, reacting it at a certain temperature for a period of time in a chlorine-containing gas atmosphere, removing heavy metals, and then washing and drying it to obtain detoxified gasification slag;

[0011] Step S2, mixing the detoxified gasified slag with the biomass powder and then roasting;

[0012] Step S3: The roasted product is acid-washed, strengthened with functional additives, and then crushed to obtain a composite carbon-based fertilizer.

[0013] Furthermore, the water-coal slurry gasification slag is crushed to 50-200 mesh, mixed with a chlorinating agent at a mass ratio of 1:0.2-0.8, and reacted at 250-500° C. for 0.5-3 hours in a chlorine-containing gas atmosphere; the chlorinating agent is selected from at least one of calcium chloride, magnesium chloride, and ferric chloride, and the chlorine-containing gas is chlorine gas, hydrogen chloride gas, or a mixture of the two, with a flow rate of 0.5-3 L / min.

[0014] Furthermore, in step S1, the fumed slag after heavy metal removal is placed in a container, deionized water with a resistivity of ≥18.2 MΩ·cm is added, and water is added at a ratio of 10 mL / g per mass of the solid phase product. The mixture is magnetically stirred at 300 rpm for 10 minutes, allowed to stand for 5 minutes, and the supernatant is discarded. This process is repeated three times until all soluble impurities are substantially removed. The washed slag is then spread on a porcelain dish and dried in a ventilated oven at 105°C for 12 hours until the sample reaches a constant weight (mass change before and after <0.1%).

[0015] The mechanism of chlorination detoxification is as follows:

[0016] In a Cl2 / HCl atmosphere at 250–500 °C, heavy metal elements (such as Pb, Cd, As) in coal-water slurry gasification slag react with Cl - The reaction generates low-melting-point or volatile metal chlorides (e.g., PbCl2, CdCl2, AsCl3), which are removed by high-temperature airflow within the tubular reactor, achieving a removal rate of ≥96%. A subsequent water wash step (solid-to-liquid ratio of 1:5–10) completely removes any remaining soluble chlorides, ensuring a metal residue of ≤5 ppm without disrupting the in-situ aluminosilicate framework.

[0017] Furthermore, step S2 specifically comprises mixing the obtained detoxified gasified slag with biomass powder in a certain mass ratio, adding an alkaline activator and a transition metal catalyst, and roasting under staged temperature control conditions.

[0018] Furthermore, the biomass powder in step S2 is selected from at least one of straw, sawdust, fruit shell, and rice husk, has a particle size of 10-100 mesh, a moisture content of ≤15%, and a mass ratio of the biomass to the detoxified gasified slag of 1:0.8-4.

[0019] Furthermore, the roasting under the staged temperature control conditions in step S2 includes the following three stages:

[0020] In the first stage, the reaction is carried out in an oxidizing atmosphere at a constant temperature for a period of time while water vapor or an oxygen-containing gas is introduced simultaneously. An air / nitrogen mixture containing 5 vol% O2 at a total flow rate of 200 mL / min is introduced, while water vapor (approximately 10 vol%, equivalent to 10 mL / min) generated by a 95°C water bath is simultaneously introduced into the reaction zone along with the carrier gas. The temperature is maintained at 290-310°C for 2 hours to ensure surface hydroxylation of the slag and promote oxidation reactions, removing small amounts of organic impurities and introducing surface –OH functional groups.

[0021] Stage 2: In a reducing or anoxic atmosphere, the reaction is heated to a specific temperature for a period of time. After the first stage, the atmosphere is switched to one of the following reducing atmospheres: pure nitrogen, a hydrogen-nitrogen mixture containing 1–10 vol% H₂, or a methane-inert gas mixture containing 3–5 vol% CH₄, at a total flow rate of 300 mL / min, which can be fine-tuned based on the equipment and sample size. The temperature is then increased from 300°C to 600°C at a rate of 10°C / min and held at 600°C for 1 hour. These high-temperature reducing / anoxic conditions further remove residual oxygen functional groups from the material surface, promoting the rearrangement of the carbon-based framework and the formation of pores, laying the foundation for subsequent functional group adjustment and optimization of sustained-release properties. If stronger reducing properties are desired, the methane volume fraction can be increased to 5 vol%, but should not exceed 10 vol% to prevent excessive carbon deposition due to methane thermal decomposition.

[0022] The third stage involves introducing a CO2-containing gas and regulating the stability of the functional groups at a specific temperature. This third stage involves switching to a pure CO2 atmosphere at a flow rate of 250 mL / min and maintaining it at 400°C for 1.5 hours. This allows the reaction of CO2 with the active sites on the material's surface to regulate the distribution and stability of the surface oxygen-containing functional groups. This stage moderately "passivates" the carbon-based structure at moderate temperatures, optimizing the material's adsorption and sustained-release properties.

[0023] The mechanism of segmented temperature-controlled roasting and structure construction is as follows:

[0024] The first stage (low-temperature oxidation): At 300–450°C, in air or 5–30% O2 / N2 atmosphere, the biomass and detoxified residue surfaces undergo mild oxidation to form a preliminary porous carbon skeleton. Under the action of water vapor (0.1–0.5 bar), oxygen-containing functional groups such as hydroxyl (–OH) and carboxyl (–COOH) are introduced to provide reaction sites for subsequent activation.

[0025] The second stage (medium temperature reduction): 500–700 ° C, H2 / N2 or inert low oxygen atmosphere, promote the graphitization of carbon skeleton and metal particles (nano-Fe 0 / Fe3O4) are highly dispersed; the metal catalyst accelerates the recombination of organic carbon-carbon bonds through a Fischer-Tropsch synthesis-like mechanism, achieving the nucleation and growth of a multi-level microporous-mesoporous network.

[0026] The third stage (CO2 activation): 1–15% CO2 is introduced at 350–550°C, which can micro-etch the carbon surface through gas-solid reaction (C+CO2→2CO), introduce stable ketone groups and carboxyl groups, and at the same time widen the pore size and optimize the mass transfer channel.

[0027] Furthermore, the alkaline activator is at least one of potassium hydroxide, sodium hydroxide, and potassium carbonate, and the addition amount is 3-20% of the total mass of the mixture; the transition metal catalyst is at least one of Fe3O4, FeCl3, MnO2 or nano zero-valent iron, with a particle size of 10-200nm, and the addition amount is 0.5-8% of the total mass of the mixture.

[0028] Furthermore, in step S3, the pickling adopts one of citric acid, oxalic acid or acetic acid solution with a concentration of 0.05-0.5 mol / L and a solid-liquid ratio of 1:3-10; the functional additive includes at least one of humic acid, potassium humate, polyacrylamide and chitosan, and the addition amount is 0.5-10% of the finished product mass.

[0029] After acid washing, the addition of citric acid, oxalic acid, or acetic acid solutions further removes inorganic residues and activates the carbon skeleton surface, generating more surface carboxyl and phenolic hydroxyl groups. Adding functional additives such as potassium humate and chitosan forms a biochar-humic acid composite structure through physical encapsulation and chemical bonding, enhancing microenvironmental complexation and improving the slow-release and retention of nutrients and water.

[0030] Furthermore, a pH-responsive slow-release membrane is coated on the surface of the obtained composite carbon-based fertilizer, and the membrane material is one of polylactic acid, polycaprolactone or silica-polyvinyl alcohol composite material.

[0031] The present invention also provides a composite carbon-based slow-release fertilizer prepared by the method for preparing a composite carbon-based slow-release fertilizer by synergistic modification of water-coal slurry gasification slag and biomass as described above.

[0032] The present invention also provides an application of the composite carbon-based slow-release fertilizer as described above, which is used for pH adjustment of saline-alkali land (adjustment range 0.3-1.5 units), remediation of heavy metal-contaminated soil, and water conservation and fertilization in arid areas; as a slow-release carrier to load pesticides, microbial agents or trace elements. The multi-level pores of the composite carbon-based slow-release fertilizer prepared by the present invention are combined with high-density surface functional groups (carboxyl ≥1.8mmol / g, hydroxyl ≥1.2mmol / g) to achieve step-by-step diffusion and dissociation of nutrients (N, P), with a 28d release rate of ≤25%, which meets the NY / T 3040-2016 slow-release standard. The mesopores and macropores are combined with surface hydrophilic groups to increase the soil water holding capacity by ≥25%, alleviating drought stress. The residual aluminosilicate skeleton releases trace Ca 2+ Mg 2+ Regulate soil pH (increase pH 0.3-1.5 units), while the high-density negative surface and humic acid complexation solidify heavy metals to achieve contaminated soil remediation.

[0033] Compared with the prior art, the present invention has the following excellent effects:

[0034] 1. High efficiency detoxification and low residue

[0035] The total amount of Pb, Cd, and As in the composite carbon-based slow-release fertilizer is ≤5ppm, and the removal rate is ≥96%, fully meeting the requirements of GB / T23349-2009 "Limits of Toxic and Hazardous Substances in Fertilizers". Compared with the traditional acid leaching method (removal rate ≈82%), it significantly reduces the risk of heavy metal residues and ensures food safety and soil health.

[0036] 2. Multi-level pores and high functional group density

[0037] The composite carbon-based slow-release fertilizer has micropores (0.5–2 nm), mesopores (2–50 nm), and macropores (50–500 nm) with a porosity of 50–85% and a specific surface area of ​​280–350 m 2 / g (GB / T19587-2017 compliant). Carboxyl groups ≥1.8mmol / g, hydroxyl groups ≥1.2mmol / g, meeting the industry standard NY525-2012 "Organic Fertilizer." Multi-level pores provide an ideal mass transfer network for nutrients and water, while high-density functional groups enhance nutrient adsorption and complexation capabilities.

[0038] 3.Excellent sustained-release performance

[0039] The 28-day cumulative nitrogen and phosphorus release rate of the composite carbon-based slow-release fertilizer is ≤25%, far lower than the 42% of the control, and fully complies with NY / T3040-2016 "Determination of nutrient release rate of slow-release fertilizers". The slow-release performance can significantly reduce nutrient loss and fertilization times, and improve fertilizer utilization efficiency.

[0040] 4. Enhance water retention and soil remediation functions

[0041] The application of composite carbon-based slow-release fertilizer increased soil water holding capacity by more than 25%, effectively alleviating drought stress; through a before-and-after comparison with HJ / T166-2004 "Technical Specifications for Soil Environmental Monitoring", the exchangeable Pb, Cd, and As in the soil decreased by ≥60%, proving the complexation and solidification effect of surface humic acid and –COOH / –OH groups on heavy metals.

[0042] 5. Low raw material cost and high resource utilization

[0043] Based on market prices (chlorination agent 1500-2500 yuan / t, agricultural waste 0-200 yuan / t) and energy consumption calculations, the preparation cost of the present invention is 780-820 yuan / t, which is 20-30% lower than the traditional process (≈1100 yuan / t); every 1t of gasification slag combined with 2t of biomass can produce ≈3t of compound fertilizer, and the comprehensive utilization rate of solid waste is ≥95%, which is in line with the circular economy and green agricultural development strategy.

[0044] 6. Strong process controllability and wide application range

[0045] The three-stage temperature control (300–450°C, 500–700°C, 350–550°C) and atmosphere (air / O2 / N2 / CO2) can be flexibly optimized according to the type of raw materials and target performance; the chlorinating agent (Ca / Mg / Fe), activating agent (KOH / NaOH / K2CO3) and biomass (rice husk / straw / sawdust / fruit shell) can be replaced at will, and the microstructure and sustained-release characteristics are stable and repeatable; the equipment used (tubular reactor, rotary kiln, analytical instruments) are all conventional industry devices, with good industrialization prospects and market promotion potential. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 It is a process flow chart of the present invention;

[0047] Figure 2 The scanning electron microscope (SEM) image of the compound fertilizer of Example 1;

[0048] Figure 3 This is a comparison chart of the slow-release performance of nitrogen and phosphorus nutrients between the composite carbon-based slow-release fertilizer prepared by the present invention and traditional fertilizers;

[0049] Figure 4 The figure is a comparison of Fourier transform infrared spectra (FTIR) of the compound fertilizer in Example 1 and the traditional fertilizer. DETAILED DESCRIPTION

[0050] The following will be combined with the accompanying drawings in the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. The technical solutions of the present invention are further explained below with reference to implementation cases.

[0051] The instruments and standards involved in the measurement of parameters in the following embodiments are as follows:

[0052] Heavy metal residue test: ICP-MS (model: iCAPMX SkimmerConePt (Boronfree), ThermoFisher Scientific, USA), implementing the standard GB / T23349-2009 "Limits of Toxic and Hazardous Substances in Fertilizers";

[0053] Porosity and specific surface area test: AutoPore IV 9500 mercury intrusion instrument (model: AutoPore IV 9500, Micromeritics, USA);

[0054] ASAP2020 nitrogen adsorption-desorption instrument (model: ASAP2020, Micromeritics, USA), implemented in accordance with the standard GB / T19587-2017 "Determination of specific surface area of ​​solid substances by gas adsorption BET method";

[0055] Humic acid content test: UV-2600 UV-visible spectrophotometer (model: UV-2600, Shimadzu, Japan), implementing the standard NY / T1971-2010 "Determination of humic acid content of water-soluble fertilizers";

[0056] Carboxyl / hydroxyl content test: Titrando905 automatic acid-base titrator (model: Titrando905, Metrohm, Switzerland), AvanceIII400MHz solid 13 CNMR (model: Avance III, Bruker, Germany), implementing standard NY525-2012 "Organic Fertilizer";

[0057] Sulfonic acid content test: iS50 FT-IR (model: iS50, ThermoNicolet, USA), implementing standard NY525-2012 "Organic Fertilizer";

[0058] Nitrogen and phosphorus nutrient slow-release performance testing: CMP3244 environmental incubator (model: CMP3244, Conviron, Canada) and QuikChem8500 continuous flow injection analyzer (model: QuikChem8500, Lachat, USA) were used in accordance with the NY / T3040-2016 standard "Determination of nutrient release rate of slow-release fertilizers."

[0059] Soil water holding capacity test: WP4C soil water potential meter (model: WP4C, METERGroup, USA), implementing standard NY / T886-2022 "Agricultural and forestry water retention agents".

[0060] Microstructure analysis of composite carbon-based slow-release fertilizer: Quanta450 field emission SEM (model: Quanta450, FEI, origin: United States), TecnaiG2F30TEM (model: TecnaiG2F30, FEI, origin: United States).

[0061] like Figure 1As shown, this flow chart clearly illustrates the entire process for preparing a composite carbon-based slow-release fertilizer made from gasified slag and wheat straw. It begins with the crushing of the coal-water slurry gasified slag, followed by heavy metal removal treatment with a chlorinating agent to produce detoxified gasified slag. The slag is then mixed with biomass powder, an alkaline activator, and a transition metal catalyst, followed by staged temperature-controlled roasting. Finally, the composite carbon-based slow-release fertilizer is obtained through acid washing, the addition of functional additives, and pulverization. The entire process is logically clear, with each step closely linked, demonstrating the systematic and scientific nature of this preparation method.

[0062] Example 1: Preparation of gasified slag-wheat straw compound fertilizer

[0063] Step S1, 1.00 kg of water-coal slurry gasification slag (crushed to 100 mesh, As content 120 ppm) and 0.40 kg of calcium chloride were mixed in a twin-shaft mixer for 30 min and then placed in a tubular furnace. Cl2 gas (1.8 L / min) was introduced and the temperature was increased to 380 ° C at 8 ° C / min and maintained for 1.5 h; after the reaction was completed, it was naturally cooled to 80 ° C, and the resulting product was stirred with deionized water (resistivity ≥18.2 MΩ·cm, 10 mL / g) at 300 rpm×10 min, allowed to stand for 5 min, and then the supernatant was discarded. After repeating 3 times, it was dried at 105 ° C for 12 h to constant weight to obtain detoxified gasification slag (As residue 1.8 ppm).

[0064] Step S2: 1.00 kg of the detoxified gasified slag, 2.00 kg of wheat straw powder (40 mesh, 8% moisture), 0.15 kg of KOH, and 0.03 kg of Fe3O4 nanoparticles are mixed evenly, and then roasted in a rotary kiln in three stages:

[0065] Stage 1: In an atmosphere of air (5 L / min) + steam (0.6 L / min), the temperature was raised to 250 °C at a rate of 10 °C / min and maintained for 1.5 h;

[0066] The second stage: switch to 3% O2 ​​in N2, gas flow rate is 300mL / min, temperature is raised to 400℃ and maintained for 40min;

[0067] The third stage: reduce the temperature to 300°C and introduce 5 vol% CO2 / N2 for 30 minutes at a gas flow rate of 2 L / min to obtain a calcined product.

[0068] Step S3: The roasted product is acid-washed with 0.1 mol / L citric acid (solid-liquid ratio 1:10) until neutral, filtered, and dried at 105° C. for 12 h. 3 wt % potassium humate (purity 90%) is then added, mixed evenly, and crushed to 60 mesh to obtain the final composite carbon-based slow-release fertilizer.

[0069] Performance test results: specific surface area and porosity were determined to be 75.2%; humic acid activity was 18.5%; and the cumulative nitrogen release rate after 28 days was 23.8%.

[0070] Figure 2 This is a scanning electron microscope (SEM) image of the compound fertilizer of Example 1. As can be observed from the figure, the compound fertilizer has a rich multi-level pore structure with a relatively uniform pore distribution and different pore sizes. These pores are interconnected, forming a complex network structure. This microstructure gives the fertilizer a large specific surface area, providing good spatial conditions for the adsorption and slow release of nutrients, while also facilitating the transmission of moisture and air in the soil, which is of great significance for improving the water retention performance of the fertilizer and the soil improvement effect.

[0071] Example 2: Preparation of Fumed Slag-Pine Sawdust Composite Fertilizer

[0072] Step S1, 1.00 kg of water-coal slurry gasification slag (crushed to 120 mesh, As content 85 ppm) and 0.50 kg of calcium chloride were mixed in a biaxial mixer for 30 min and then placed in a tubular furnace. Cl2 gas (2 L / min) was introduced and the temperature was increased to 450 ° C at 10 ° C / min and maintained for 2 h; after the reaction was completed, it was naturally cooled to 80 ° C, and the resulting product was stirred with deionized water (resistivity ≥18.2 MΩ·cm, 10 mL / g) at 300 rpm × 10 min, allowed to stand for 5 min, and then the supernatant was discarded. This was repeated 3 times and then dried at 105 ° C for 12 h to constant weight to obtain detoxified gasification slag (As residue 1.2 ppm).

[0073] Step S2: 1.00 kg of the detoxified gasified slag, 3.00 kg of wheat straw powder (60 mesh, 9% moisture content), 0.15 kg of KOH, and 0.04 kg of Fe3O4 nanoparticles are mixed evenly, and then roasted in a rotary kiln in three stages:

[0074] The first stage: in an atmosphere of air (5 L / min) + steam (0.8 L / min), the temperature was raised to 280 °C at a rate of 10 °C / min and maintained for 8 h;

[0075] Stage 2: switch to 2% O2 in N2 (300 mL / min), increase the temperature to 450°C and hold for 30 min;

[0076] The third stage: reduce the temperature to 300°C and introduce 6 vol% CO2 / N2 (2 L / min) for 30 minutes to obtain the calcined product.

[0077] Step S3, the roasted product is acid-washed with 0.1 mol / L citric acid (solid-liquid ratio 1:10) until neutral, filtered, and dried at 105°C for 12 hours, and then 5 wt% chitosan (powdered) is added, uniformly mixed, and crushed to 60 mesh to obtain a composite carbon-based slow-release fertilizer.

[0078] The test results show that the sulfonic acid group density of the prepared composite carbon-based slow-release fertilizer is 0.62mmol / g, and the Ca2+ The adsorption capacity is 135 mg / g, showing excellent functional performance.

[0079] Comparative Example 1: Traditional acid leaching detoxification (without staged roasting)

[0080] 1 kg of gasified slag was leached with 10% sulfuric acid (solid-liquid ratio 1:5, stirring at 80°C for 2 hours), with an As removal rate of 82% and a porosity of 38%. It was directly mixed with straw for carbonization (500°C / 2 hours), with a humic acid content of 7.2% and a carboxyl density of 0.7 mmol / g.

[0081] Results: The nitrogen release rate was 42% in 28 days, and soil pH adjustment was ineffective.

[0082] Example 3: Low-cost rice husk-based fertilizer

[0083] 1 kg (80 mesh) of coal-water slurry gasification slag was mixed with 0.3 kg of CaCl₂ at 300°C and 1 L / min of chlorine for 1 hour, resulting in an As residual of 3.5 ppm (still meeting the standard). The slag was then calcined in stages with 1 kg of rice husk (20 mesh), 0.1 kg of KOH, and 0.02 kg of FeCl₃. The slag was then heated in a rotary kiln at a rate of 10°C / min to 200°C, with air (5 L / min) and steam (0.5 L / min) introduced. The temperature was then maintained at this temperature for 3 hours. The slag was then switched to a low-oxygen atmosphere (5% O₂ in N₂), heated to 350°C, and held at this temperature for 1 hour. The slag was then cooled to 300°C and treated with a 6% CO₂ / N₂ mixture (2 L / min) for 30 minutes. The slag was then washed with 0.05 mol / L citric acid and 1% humic acid was added.

[0084] Performance test: Humic acid activity: 12.3%; cost reduced by 22% compared with Example 1, suitable for low-salinity soil improvement.

[0085] Table 1 Comparison of key data

[0086]

[0087] Compared with other solutions, the gasified slag-wheat straw composite carbon-based slow-release fertilizer prepared in Example 1 showed excellent comprehensive performance: its As residual content was reduced from 120ppm to 1.8ppm, that is, a removal rate of 98.50%, which was much better than the traditional acid leaching method (Comparative Example 1, 82% removal rate) and Example 3 (92% removal rate), and was equivalent to Example 2 (98.80% removal rate); the specific surface area and porosity reached 75.2%, which was slightly lower than 78.1% of Example 2, but significantly higher than 38% of Comparative Example 1 and 58% of Example 3; after washing with citric acid, 3wt% potassium humate was loaded, and the activity was 18.5%, The results are as follows: the 28-day cumulative nitrogen release rate is 23.8%, which maintains a relatively stable slow-release characteristic and is better than 19.5% in Example 2 and 28% in Example 3 (42% in Comparative Example 1, which releases too quickly and easily causes nutrient loss); the preparation cost is 780 yuan / ton, which is not only lower than 820 yuan / ton in Example 2, but also significantly lower than 1,100 yuan / ton in Comparative Example 1. Although it is slightly higher than 610 yuan / ton in Example 3, combined with its better detoxification and nutrient management capabilities, Example 1 achieves the best balance between performance and economy.

[0088] Figure 3 The slow-release performance of nitrogen and phosphorus nutrients in this composite carbon-based slow-release fertilizer was compared with that of traditional fertilizers. Clearly, over a 28-day test period, the cumulative nitrogen and phosphorus release rate of this composite fertilizer was significantly lower than that of traditional fertilizers and remained consistently low, meeting the NY / T 3040-2016 slow-release standard. This demonstrates the fertilizer's excellent slow-release properties, enabling the slow release of nutrients, reducing nutrient loss, improving fertilizer utilization, and reducing fertilization frequency and costs.

[0089] Figure 4 The Fourier transform infrared spectrum (FTIR) of the compound fertilizer of Example 1 and the traditional fertilizer is compared. As can be seen from the spectrum, at 3441cm -1 There is an obvious -OH stretching vibration absorption peak near 1632cm -1 The stretching vibration absorption peak of C=O is at 1400 cm -1 Nearby is the bending vibration absorption peak of CO, 873cm -1 and 1099cm -1 The peaks at the 300 nm peaks correspond to the bending vibration of CH and the stretching vibration of CO, respectively. Compared to traditional fertilizers, the compound fertilizer exhibits significant differences in the intensities of these characteristic peaks, indicating the presence of abundant -OH and -COOH functional groups on its surface. These functional groups enhance the fertilizer's ability to adsorb and complex nutrients, while also facilitating complexation reactions with heavy metal ions in the soil, thereby solidifying the heavy metals and enhancing soil remediation.

[0090] The above-described embodiments merely illustrate several implementations of the present invention. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, and all such variations and improvements fall within the scope of protection of the present invention.

Claims

1. A method for preparing a composite carbon-based slow-release fertilizer by synergistic modification of coal-water slurry gasification slag and biomass, characterized in that: The following steps are involved: Step S1, crushing the water-coal slurry gasification slag and mixing it with a chlorinating agent in a certain mass ratio, reacting it at a certain temperature for a period of time in a chlorine-containing gas atmosphere, removing heavy metals, and then washing and drying it to obtain detoxified gasification slag; Step S2, mixing the detoxified gasified slag with the biomass powder and then roasting; Step S3: The roasted product is acid-washed, strengthened with functional additives, and then crushed to obtain a composite carbon-based fertilizer.

2. The method for preparing composite carbon-based slow-release fertilizer by synergistic modification of coal water slurry gasification slag and biomass according to claim 1, characterized in that: The water-coal slurry gasification slag is crushed into 50-200 meshes, mixed with a chlorinating agent at a mass ratio of 1:0.2-0.8, and reacted at 250-500°C for 0.5-3 hours in a chlorine-containing gas atmosphere; the chlorine-containing gas is chlorine gas, hydrogen chloride gas or a mixture of the two, with a flow rate of 0.5-3 L / min.

3. The method for preparing composite carbon-based slow-release fertilizer by synergistic modification of coal water slurry gasification slag and biomass according to claim 1, characterized in that: In step S1, the gasified slag after heavy metal removal is placed in a container, deionized water with a resistivity of ≥18.2 MΩ·cm is added, and the mixture is magnetically stirred and allowed to stand, and the supernatant is discarded. The above operation is repeated three times, and the washed slag is spread in a porcelain dish and placed in a ventilated oven to dry at 105°C for 12 hours.

4. The method for preparing composite carbon-based slow-release fertilizer by synergistic modification of coal water slurry gasification slag and biomass according to claim 1, characterized in that: Step S2 specifically comprises mixing the obtained detoxified gasified slag with biomass powder in a certain mass ratio, adding an alkaline activator and a transition metal catalyst, and roasting under staged temperature control conditions.

5. The method for preparing composite carbon-based slow-release fertilizer by synergistic modification of water-coal slurry gasification slag and biomass according to claim 4, characterized in that: The biomass powder in step S2 is selected from at least one of straw, sawdust, fruit shell, and rice husk, has a particle size of 10-100 mesh, a moisture content of ≤15%, and a mass ratio of the biomass to the detoxified gasified slag of 1:0.8-4.

6. The method for preparing composite carbon-based slow-release fertilizer by synergistic modification of water-coal slurry gasification slag and biomass according to claim 4, characterized in that: The roasting under the staged temperature control conditions in step S2 includes the following three stages: In the first stage, the reaction is carried out at a certain temperature for a period of time in an oxidizing atmosphere, and water vapor or oxygen-containing gas is introduced simultaneously; The second stage: in a reducing or oxygen-deficient atmosphere, the temperature is raised to a certain temperature and reacted for a period of time; The third stage: introducing CO2-containing gas to regulate the stability of functional groups at a certain temperature.

7. The method for preparing composite carbon-based slow-release fertilizer by synergistic modification of coal water slurry gasification slag and biomass according to claim 4, characterized in that: The alkaline activator is at least one of potassium hydroxide, sodium hydroxide, and potassium carbonate, and the addition amount is 3-20% of the total mass of the mixture; the transition metal catalyst is at least one of Fe3O4, FeCl3, MnO2 or nano zero-valent iron, with a particle size of 10-200nm, and the addition amount is 0.5-8% of the total mass of the mixture.

8. The method for preparing composite carbon-based slow-release fertilizer by synergistic modification of coal water slurry gasification slag and biomass according to claim 1, characterized in that: In step S3, the pickling is performed using one of citric acid, oxalic acid or acetic acid solutions with a concentration of 0.05-0.5 mol / L and a solid-liquid ratio of 1:3-10; the functional additives include at least one of humic acid, potassium humate, polyacrylamide and chitosan, and the added amount is 0.5-10% of the finished product mass.

9. A composite carbon-based slow-release fertilizer prepared according to the method for preparing a composite carbon-based slow-release fertilizer by synergistic modification of water-coal slurry gasification slag and biomass according to any one of claims 1 to 8.

10. Use of the composite carbon-based slow-release fertilizer according to any one of claims 1 to 9, characterized in that: It is used for pH adjustment of saline-alkali land, remediation of heavy metal-contaminated soil, and water conservation and fertilization in arid areas; and as a slow-release carrier for loading pesticides, microbial agents or trace elements.

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