Phosphorus-rich functional fertilizer and preparation method and application thereof

Abstract

This invention discloses a phosphorus-rich functional fertilizer, its preparation method, and its application. The phosphorus-rich functional fertilizer includes a porous solid waste ceramic framework with a Mg-La double hydroxide active layer on its surface. The Mg-La double hydroxide active layer chemically bonds and releases phosphorus components; the loading of the slow-release phosphorus components is 1481~1511 mg / kg. The preparation method includes the following steps: gradient sintering of fly ash, municipal sludge, power plant slag, and cement at 600~1050℃, loading the Mg-La double hydroxide active layer, and allowing it to stand in a potassium dihydrogen phosphate solution. This invention also discloses the application of the phosphorus-rich functional fertilizer in slow-release fertilizers or soil conditioners for farmland soil. This invention realizes the agricultural recycling of phosphorus resources, utilizes the honeycomb porous structure of the solid waste matrix to improve the soil microenvironment, achieves the tiered slow release and synergistic effect of multiple nutrients, and ensures the long-term safety and economy of returning solid waste to the field.

Description

Technical Field

[0001] This invention pertains to fertilizers, their preparation methods and applications, specifically a phosphorus-rich functional fertilizer, its preparation method and application. Background Technology

[0002] Phosphorus, one of the three essential nutrients for plant growth, is a non-renewable mineral resource. However, current phosphate fertilizer production relies excessively on limited phosphate rock resources. Simultaneously, the discharge of large amounts of phosphorus-containing wastewater leads to eutrophication of water bodies, not only wasting resources but also disrupting the aquatic ecological balance. Therefore, how to efficiently recover phosphorus from wastewater and realize its resource utilization has become a research hotspot.

[0003] On the other hand, the amount of industrial solid waste such as fly ash, municipal sludge and power plant slag is increasing year by year. Long-term stockpiling not only occupies a large amount of land, but also poses a risk of polluting surface water and groundwater due to the trace heavy metals and harmful substances contained therein. Although some studies have been conducted to prepare it into adsorbent materials such as ceramsite for phosphorus removal, the following defects still exist: (1) Incomplete resource utilization: After the existing adsorbent materials are saturated, they are often used as solid waste for secondary landfill or simple downgrading, failing to achieve a complete closed loop from "waste" to "high-value product". (2) Poor nutrient release performance: When traditional phosphorus-rich adsorbent products are used as fertilizers, the phosphorus release kinetics are unbalanced, making it difficult to meet the needs of the entire crop growth cycle, and phosphorus lock-in is easy to occur. (3) Single function: Existing fertilizer research focuses more on phosphorus supply, ignoring the potential synergistic effect of the physical structure of the solid waste matrix itself (such as pore moisture retention) and endogenous mineral elements (such as magnesium, calcium and rare earth elements) on plant physiological metabolism. (4) Environmental risk concerns: After solid waste-based fertilizers are applied to the soil, the long-term environmental stability of their heavy metals and their safety to crops remain the main bottlenecks restricting their large-scale agricultural application.

[0004] Therefore, developing a compound functional fertilizer that can efficiently recover phosphorus from wastewater and utilize the physical and chemical properties of multi-source solid waste to achieve stable and slow-release of nutrients and has physiological regulatory functions is of great scientific significance and application value for promoting "waste treatment" and "resource recycling". Summary of the Invention

[0005] Purpose of the invention: In order to overcome the shortcomings of the existing technology, the purpose of this invention is to provide a phosphorus-enriched functional fertilizer that synergistically enhances the effects of multiple solid waste sources, to provide a simple and convenient method for preparing the phosphorus-enriched functional fertilizer, and to provide an application of the phosphorus-enriched functional fertilizer in slow-release fertilizers or soil conditioners for farmland soil.

[0006] Technical solution: The present invention provides a phosphorus-rich functional fertilizer comprising a porous solid waste ceramic skeleton, wherein a Mg-La double hydroxide active layer is disposed on the surface of the porous solid waste ceramic skeleton, and the Mg-La double hydroxide active layer is chemically bonded to a slow-release phosphorus component; the loading of the slow-release phosphorus component is 1481~1511 mg / kg.

[0007] Furthermore, the slow-release phosphorus component is immobilized on the surface of the active layer in the form of La-P and Mg-OP inner layer complexes. The adsorption behavior of phosphorus by the phosphorus-rich functional fertilizer conforms to the Sips isothermal adsorption model, which has a heterogeneity coefficient of 0.81~0.83.

[0008] Furthermore, the porous solid waste ceramic skeleton is made of fly ash, municipal sludge, power plant slag, and cement sintering, and has mullite and anorthite main crystalline phases.

[0009] Furthermore, fly ash comprises the following substances in mass percentage: 30-32 wt% Al2O3, 6-7 wt% Fe2O3, 7-8 wt% CaCO3, 1-2 wt% MgO, 1-2 wt% K2O, 1-2 wt% Na2O, with the balance being SiO2.

[0010] Furthermore, municipal sludge comprises the following substances by mass percentage: 20-22 wt% Al2O3, 11-12 wt% Fe2O3, 6-7 wt% CaCO3, 2-3 wt% MgO, 2-3 wt% K2O, 0.5-1 wt% Na2O, with the balance being SiO2.

[0011] Furthermore, the power plant slag comprises the following substances by mass percentage: 36~38 wt% Al2O3, 7~8 wt% Fe2O3, 7~8 wt% CaCO3, 0.5~1 wt% MgO, 0.5~1 wt% K2O, 0.5~1 wt% Na2O, with the balance being SiO2.

[0012] Furthermore, the cement comprises the following substances in weight percentages: 20-22 wt% SiO2, 6-7 wt% Al2O3, 3-4 wt% Fe2O3, 2-3 wt% MgO, 0.5-1 wt% K2O, 0.1-0.5 wt% Na2O, with the balance being CaCO3.

[0013] Furthermore, the porous solid waste ceramic skeleton has a porosity ≥ 50.31% and a specific surface area of ​​0.9 × 10⁻⁶. 4 ~1×10 4 cm 2The average pore size is 5-7 nm. The sum of the breakage rate and wear rate of the porous solid waste ceramic skeleton is ≤0.238%, the mud content is ≤0.541%, the hydrochloric acid solubility is ≤0.792%, and the density is 1942.2 kg / m³. 3 The bulk density is 473.4 kg / m³. 3 .

[0014] Furthermore, the Mg-La LDH active layer is mainly composed of a layered framework of magnesium (Mg) and lanthanum (La) and carbonate (CO3) as an interlayer anion. 2- The active layer is composed of metal hydroxide groups (M-OH) and metal oxide bonds (MO), specifically including active sites such as La-OH, Mg-OH, La-O, and Mg-O. XRD and SEM characterization revealed that the loaded ceramic particles formed a highly crystalline La(CO3)2(OH)2 phase on their surface, exhibiting a characteristic layered nanosheet structure. These structures provide numerous available sites for the effective capture of phosphorus.

[0015] The preparation method of a phosphorus-rich functional fertilizer according to the present invention includes the following steps: sintering fly ash, municipal sludge, power plant slag, and cement at a gradient temperature of 600~1050℃, loading a Mg-La double hydroxide active layer, and then allowing it to stand in a potassium dihydrogen phosphate solution.

[0016] This invention provides the application of a phosphorus-rich functional fertilizer in slow-release fertilizers or soil conditioners for farmland soil.

[0017] Furthermore, the amount of phosphorus-rich functional fertilizer added is 1-2% of the soil mass.

[0018] Preparation Principle: The preparation principle of phosphorus-enriched ceramsite as a slow-release fertilizer is mainly based on the strong chemical bond formed between the Mg-LaLDH active layer and phosphate. Unlike traditional physical adsorption or simple impregnation techniques, this material forms extremely stable La-P and Mg-OP complexes on the surface through internal spherical complexation, accompanied by partial anion exchange and interlayer intercalation. This chemical phosphorus fixation mechanism prevents phosphorus from being rapidly lost like ordinary fertilizers, instead exhibiting a controlled slow-release curve, still possessing significant nutrient supply potential after 14 release cycles. Furthermore, the porous structure of the ceramsite itself effectively improves soil water retention and aeration, and the magnesium and lanthanum elements in the active layer produce synergistic physiological effects, significantly enhancing plant photosynthetic efficiency and growth vitality by stimulating enzyme activity and promoting chlorophyll biosynthesis.

[0019] In terms of technological advancement, this research overcomes the limitations of existing technologies (such as metal-impregnated ceramsite or biochar-based adsorbents). Compared to existing materials with poor mechanical strength, difficulty in recycling, and limited biomass enhancement, this fly ash-sintered ceramsite not only achieves a fully closed-loop resource utilization of solid waste, but also exhibits a more significant growth-promoting effect, with experiments showing an increase in plant dry weight of up to 106.8%. More importantly, the high-temperature sintering process, while imparting high strength to the ceramsite, effectively blocks the leaching risk of heavy metals from fly ash, ensuring its environmental safety as an agricultural fertilizer and solving the problem of insufficient mechanical stability and secondary pollution risks associated with traditional carriers in practical applications.

[0020] Beneficial effects: Compared with the prior art, the present invention has the following significant features:

[0021] 1. Through the collaborative innovation of the entire process of "adsorption-conversion-resource utilization", a closed-loop utilization from industrial solid waste to functional phosphate fertilizer has been realized. By utilizing Mg-LaLDH modified ceramsite to efficiently capture phosphorus in wastewater (saturated adsorption capacity of 1496.52mg / kg), the originally difficult-to-treat phosphorus in wastewater is transformed into slow-release phosphate fertilizer with high added value. This not only overcomes the problem of difficult disposal after adsorption by traditional adsorbents, but also realizes the agricultural cycle of phosphorus resources through "waste treatment", which has significant dual attributes of resource saving and environmental governance.

[0022] 2. Fully utilize the honeycomb porous structure of solid waste substrate to improve the soil microenvironment. This utilizes a substrate formed by sintering solid waste such as fly ash and sludge, possessing a porosity of 50.31% and a density of 0.9694 × 10⁻⁶. 4 cm 2 The porous ceramic framework with a surface area of ​​ / g can play an excellent role in moisture retention and aeration after being applied to the soil. Experiments on Chinese cabbage show that this physical structure can provide excellent moisture and air conditions for seed germination, significantly increasing the seed germination rate of crops from 69.7% to 93.9%, solving the problem that traditional fertilizers can easily lead to soil compaction and reduce germination rate.

[0023] 3. It achieves the tiered slow release and synergistic effect of multiple nutrients. The constructed phosphorus-rich functional fertilizer not only provides a stable phosphorus source for up to 14 release cycles, but also releases mineral elements such as magnesium, lanthanum, and calcium in synergistic way through the Mg-LaLDH modified layer and solid waste matrix. The synergistic release of magnesium and phosphorus significantly promotes plant photosynthesis, increasing the chlorophyll content of crop leaves by 25.4%. Under the synergistic stimulation of multiple elements, the crop exhibits a strong biomass accumulation capacity. Pot experiments show that the dry weight of Chinese cabbage increased by as much as 106.8% compared with the blank control group. This dual function of "nutrient supply + physiological regulation" is significantly better than traditional fertilizers with single nutrients.

[0024] 4. This invention ensures the long-term safety and economy of returning solid waste to the field. Through high-temperature gradient sintering at 1050℃, harmful heavy metals in solid waste are firmly locked in the mullite and anorthite lattice. The concentrations of chromium, arsenic, lead, zinc, nickel and other substances in the leachate are far below the Class I limit of the "Surface Water Environmental Quality Standard" (As=0.152g / L, Ni=2.72g / L), eliminating the safety hazards of solid waste resource utilization from the source. At the same time, the fertilizer has low production cost and high added value. While treating phosphorus pollution in water bodies, it also improves agricultural output, achieving a high degree of unity between environmental, social and economic benefits. Attached Figure Description

[0025] Figure 1 The images show the XRD patterns of the ceramsite before and after adsorption.

[0026] Figure 2 This is a comparison of the ceramsite before and after loading with LDH and its EDS graph;

[0027] Figure 3 XPS images of ceramsite before and after adsorption;

[0028] Figure 4 The images show the XRD patterns of the modified ceramsite before and after adsorption.

[0029] Figure 5 The characteristics of circulating phosphorus release from phosphorus-rich ceramic particles;

[0030] Figure 6 This is a comparison chart of germination rates;

[0031] Figure 7 This is a diagram showing the differences in apparent growth.

[0032] Figure 8 This is a comparison chart of growth parameters. Detailed Implementation

[0033] Unless otherwise specified, all materials and reagents used in the following embodiments are commercially available. Experimental methods not specifically described in the embodiments are generally performed under standard conditions or as recommended by the manufacturer.

[0034] Table 1 Chemical composition analysis of raw materials (wt%)

[0035]

[0036] In the following embodiments, the fly ash is dry-discharged fly ash from the power plant, which is used after natural air drying; the municipal sludge is dried at 105℃ until the moisture content is ≤5% and then crushed; the power plant slag is crushed to 100±20 mesh before use; and the cement is P.O42.5 cement. To clarify the chemical composition of the raw materials in the embodiments of the present invention, X-ray fluorescence spectroscopy (XRF) was used for detection. The composition results of fly ash, municipal sludge, power plant slag, and cement are shown in Table 1.

[0037] Key instruments used in the embodiments of this invention:

[0038] (1) Spectrophotometer: Upper Analyzer Electro-Analysis, UV-5200PC (used to determine phosphorus concentration).

[0039] (2) Chlorophyll measuring instrument: Laiyin Optoelectronics, IN-YL04 (used for non-destructive testing of plant chlorophyll content).

[0040] (3) Analytical balance: FA1104, Shanghai Liangping instrument (used for weighing biomass).

[0041] (4) Electric heating constant temperature drying oven: DZF-6050, Shanghai Yiheng (used for raw material pretreatment and plant dry weight drying).

[0042] (5) Inductively coupled plasma atomic emission spectrometer: used to detect the leaching concentration of heavy metals.

[0043] (6) X-ray diffractometer: MAX-2600, Rigaku Corporation, Japan (used to analyze the crystal phase composition of the framework and LDH layer).

[0044] The detection method in this embodiment of the invention refers to:

[0045] (1) Total phosphorus in water: Determination of total phosphorus in water by ammonium molybdate spectrophotometric method (GB 11893-89).

[0046] (2) Available phosphorus in soil: Refer to the "Determination of Available Phosphorus in Soil by Sodium Bicarbonate Extraction-Molybdenum Antimony Spectrophotometric Method" (HJ 704-2014), Olsen method (sodium bicarbonate extraction).

[0047] (3) Leaching safety: Refer to the "Leaching Toxicity of Solid Waste: Horizontal Oscillation Method" (HJ 557-2010).

[0048] Example 1

[0049] A method for preparing a phosphorus-rich functional fertilizer includes the following steps:

[0050] (1) Fertilizer substrate preparation: Fly ash, sludge, desulfurized gypsum, and cement in a mass ratio of 7:3:2:1.2 were preheated to 600℃ for 5 min at a heating rate of 5℃ / min, and then heated to 1050℃ at a heating rate of 5℃ / min and held for 5 min to obtain a porous solid waste ceramic skeleton. The porosity of the porous solid waste ceramic skeleton was 51%, and the specific surface area was 0.9694×10⁻⁶. 4 cm 2 It has a mesoporous distribution with an average pore size of 6.5 nm.

[0051] (2) The loading amounts of Mg and La were precisely controlled through precursor ratio, solid-liquid ratio, and loading process parameters. During the synthesis of the Mg-La LDH slurry, the molar ratio of Mg(NO3)2·6H2O to La(NO3)3·6H2O was strictly set to 4.0 to determine the chemical basis of the active ingredients. Subsequently, the pretreated ceramic particles were immersed in the Mg-La LDH slurry at a solid-liquid ratio of 1:10 g / mL, and continuous stirring for 4 hours was used to ensure sufficient adhesion and growth of the active substances on the surface of the ceramic particles. Finally, the ceramic particles were repeatedly rinsed with deionized water until neutral (pH 7.0±0.5) and dried and solidified at 105℃ to achieve the final fixation of the active loading amount, thus loading a Mg-La double hydroxide active layer onto the surface of the porous solid waste ceramic skeleton.

[0052] (3) Phosphorus nutrient enrichment: Potassium dihydrogen phosphate (KH2PO4) was used to prepare simulated phosphorus-containing wastewater with an initial phosphorus concentration of 500 mg / L.

[0053] (4) Conversion preparation: The product obtained in step (2) is put into the simulated phosphorus-containing wastewater in step (3), and the solid-liquid ratio is controlled at 100g / L (for example, 10g of ceramic particles are added to 100ml of wastewater). The ceramic particles are shaken at 150rpm for 24h at 25℃ to allow the active sites on the surface of the ceramic particles to fully react with the phosphorus in the aqueous phase and reach the adsorption saturation state.

[0054] (5) Post-processing: After the reaction is completed, the ceramic particles are filtered out, and the surface residual free phosphorus is gently washed with deionized water. The particles are then placed in an electric constant temperature drying oven and dried at 60°C until constant weight is obtained to obtain phosphorus-rich functional fertilizer.

[0055] Load performance verification results:

[0056] (1) XRD characterization results showed that the original ceramsite before modification was highly crystalline, with sharp and well-defined diffraction peaks, and the main crystalline phases were composed of anorthite and mullite. After Mg-La LDH surface modification, the XRD spectrum retained the original characteristic peaks of the ceramsite matrix, and new diffraction peaks belonging to La(CO3)2(OH)2 appeared.

[0057] Loading capacity: Based on the test and the fitting of the Sips isothermal adsorption model, the saturated loading capacity of phosphorus-rich functional fertilizer prepared in this embodiment reached 1496.52±15mg / kg.

[0058] (2) such as Figure 1 The original ceramsite before modification was highly crystalline, with sharp and well-defined diffraction peaks, and its main crystalline phases were composed of anorthite and mullite. After Mg-La LDH surface modification, the XRD pattern retained the original characteristic peaks of the ceramsite matrix, and new diffraction peaks belonging to La(CO3)2(OH)2 appeared.

[0059] (3) Morphology and distribution: such as Figure 2 SEM images show that the surface of the phosphorus-loaded ceramsite obtained in step (4) is densely covered with layered nanostructures; energy dispersive spectroscopy (EDS-Mapping) confirms that magnesium (Mg), lanthanum (La) and phosphorus (P) elements show a highly overlapping and uniform distribution trend on the surface of the ceramsite, proving that phosphorus has been successfully and uniformly loaded on the modified active layer.

[0060] (4) Chemical bonding mechanism: such as Figure 3 As shown in the XPS photoelectron spectroscopy, compared with before adsorption, the binding energies of lanthanum (La3d) and magnesium (Mg1s) both underwent a positive shift of approximately 0.3 eV after phosphorus adsorption; simultaneously, a significant P 2p characteristic diffraction peak appeared at 133.07 eV. This confirms at the atomic energy level that phosphate ions form stable La-P and Mg-OP inner-layer complexes through electron transfer and modification, rather than simple physical stacking, thus ensuring the smoothness of subsequent fertilizer release.

[0061] (5) such as Figure 4 The modified ceramsite (phosphate-rich functional fertilizer) obtained in step (2) maintained good crystallinity before and after adsorption, and the original phases were basically unaffected, indicating that the introduction of LDH had little impact on the structural integrity of the ceramsite. Notably, several diffraction peaks (e.g., those at 16.164°, 28.088°, and 41.063°) shifted slightly to lower angles after adsorption, suggesting that phosphate ions may have intercalated into the interlayer of LDH, leading to lattice expansion and increased interlayer spacing. This structural change provides indirect evidence for the successful adsorption of phosphate and highlights the correlation between the material's structural response and its adsorption behavior.

[0062] (6) Stability: The performance of the phosphorus-rich functional fertilizer obtained in this embodiment was tested according to the relevant standards of CJ / T 299—2008 "Artificial Ceramic Filter Media for Water Treatment". As shown in Table 2 below, it can be seen that the phosphorus-rich functional fertilizer obtained in this embodiment meets the relevant requirements of CJ / T 299—2008 "Artificial Ceramic Filter Media for Water Treatment".

[0063] Table 2 Performance data of phosphorus-enriched functional fertilizer in Example 1

[0064]

[0065] Example 2

[0066] This embodiment is used to verify the phosphorus release pattern and long-lasting effect of the phosphorus-rich functional fertilizer prepared in Example 1 in an aqueous environment. The specific steps are as follows:

[0067] (1) Preparation of experimental apparatus: Weigh 1.00g of the phosphorus-rich functional fertilizer prepared in Example 1 and place it in a 150mL conical flask. Add 100mL of deionized water as the release medium to keep the solid-liquid ratio at 10g / L.

[0068] (2) Isothermal release: Place the conical flask in an isothermal shaker and control the system temperature at 25±0.5°C. Shake continuously at 150 rpm in the dark for 24 hours.

[0069] (3) Sampling and measurement: After the release time is reached, the functional fertilizer and the release liquid are separated by filtration. The phosphorus concentration in the filtrate is measured by spectrophotometer, and the phosphorus release amount of this cycle is calculated.

[0070] (4) Cyclic release: The filtered functional fertilizer was placed back into an Erlenmeyer flask containing 100 mL of fresh deionized water, and the experimental steps (2) to (3) above were repeated. A total of 14 consecutive release cycles were carried out in this experiment, with a total experimental time of 336 h.

[0071] Results of sustained-release performance verification:

[0072] Release kinetic characteristics: such as Figure 5 As shown, the phosphorus-rich functional fertilizer prepared by this invention exhibits significant staged slow-release characteristics. During the initial three release cycles, phosphorus shows a relatively rapid release rate, which is mainly attributed to the rapid desorption of phosphorus physically attached to the surface and macropores of the ceramsite.

[0073] Long-lasting supply capacity: As the release cycle increases, phosphorus release enters a stable and slow decline phase. After completing 14 consecutive release cycles, the fertilizer still maintains a stable phosphorus output potential, and the cumulative release curve shows no plateau, demonstrating its excellent long-lasting slow-release function. This release mode effectively avoids the loss of nutrients in an instant, thus ensuring that plants receive a continuous supply of nutrients throughout their entire growth cycle.

[0074] Example 3

[0075] This embodiment is used to verify the promoting effect of the phosphorus-rich functional fertilizer prepared in Example 1 on crop seed germination and its effect on improving the soil physical microenvironment. The specific steps are as follows:

[0076] (1) Preparation of experimental substrate: Farmland soil with uniform physicochemical properties was selected as the culture substrate and hilled up for one month to ensure uniform physicochemical properties. The experiment consisted of 4 groups, with 11 replicates in each group. One seed was sown in each replicate, for a total of 44 experimental units. The group settings are as follows:

[0077] ① Blank control group (CK): Only the original soil was used, without adding any fertilizer.

[0078] ②1% Fertilizer Addition Group (C1): The functional fertilizer prepared in Example 1 was evenly mixed into the original soil, and the addition amount was 1% of the soil mass.

[0079] ③2% Fertilizer Addition Group (C2): The functional fertilizer prepared in Example 1 was evenly mixed into the original soil, and the addition amount was 2% of the soil mass.

[0080] ④ Conventional fertilizer group (CF): Add commercially available conventional phosphate fertilizer with the same phosphorus nutrient content.

[0081] (2) Sowing and cultivation: Sow 15 seeds of Chinese cabbage in each potted container at a consistent depth. Place the potted plants in a plant artificial climate chamber and control the temperature at 25 / 20°C (day / night) and the light intensity at 15000 lux. Water regularly and in measured amounts every day.

[0082] (3) Observation of indicators: Record the number of seeds germinating in each group every day after sowing. Calculate the final germination rate of each group on the 7th day.

[0083] Experimental verification results:

[0084] Germination rate significantly improved: such as Figure 6 As shown, the seed germination rate of the CK group was 69.7%. In contrast, the seed germination rates of the C1 and C2 groups, which incorporated the functional fertilizer of this invention, significantly increased to 88.5% and 93.9%, respectively. The germination rate of the CF group was only 77.4%.

[0085] Mechanism of Enhanced Effect from Physical Structure: Experimental observations revealed that the addition of functional fertilizers significantly improved the physical properties of the soil. This is mainly attributed to the well-developed honeycomb-like porous structure (porosity ≥ 50.31%) within the phosphorus-rich functional fertilizer. These pores act as miniature "water reservoirs" and "aeration pores" in the soil, maintaining root water supply while preventing soil compaction, thus creating an excellent microenvironment for seed germination. This growth-promoting effect resulting from improved physical structure is not found in traditional powdered or granular fertilizers.

[0086] Example 4

[0087] This embodiment aims to quantitatively verify the beneficial effects of phosphorus-rich functional fertilizer on crop yield and physiological metabolism, as well as its influence on the growth performance and physiological indicators of Chinese cabbage, through a complete potted plant growth cycle experiment. The specific steps are as follows:

[0088] (1) Experimental continuation and field management: The pot experiment design (groups CK, C1, C2, and CF) from Example 3 was continued. After seed germination, each pot was planted with 3 seedlings of uniform growth vigor and continued to be cultivated in an artificial climate chamber until day 30. During this period, the pot positions were adjusted every 2 days to eliminate edge effects and the soil moisture was maintained at 60%-7% of field capacity.

[0089] (2) Monitoring of physiological indicators: One day before harvest, a chlorophyll meter was used to perform non-destructive testing on the functional leaves of each group of pak choi. The measurement was repeated 5 times and the average value was taken to evaluate the effect of fertilizer on photosynthetic efficiency. At the same time, the diameter of the root and stem of pak choi was measured using a digital vernier caliper.

[0090] (3) Biomass determination: After the culture was completed, whole Chinese cabbage plants were collected. The soil attached to the plants was first rinsed with tap water and then rinsed with deionized water. The plants were placed in an electric thermostatic drying oven and blanched at 105℃ for 30 minutes. Then the temperature was adjusted to 75℃ and dried to constant weight. The dry weight was measured using an analytical balance.

[0091] Experimental verification results:

[0092] (1) Apparent growth differences: such as Figure 7 As shown, the C1 and C2 groups of Chinese cabbage treated with the functional fertilizer of this invention showed significantly better plant height, number of leaves, and root density than the CK and CF groups.

[0093] (2) Significant increase in biomass: such as Figure 8 As shown, compared with the CK group, the average dry weight of pak choy in the C2 group (2% addition) increased by 106.8%. Compared with the conventional fertilizer group (CF) with the same amount of phosphorus, the functional fertilizer of this invention showed stronger sustained nitrogen and phosphorus supply capacity and growth promotion potential.

[0094] (3) Physiological synergistic effect: The experimental results showed that the chlorophyll content (SPAD value) of the leaves of Chinese cabbage in group C2 was 25.4% higher than that in group CK.

[0095] Example 5

[0096] This embodiment is used to verify the environmental safety of phosphorus-rich functional fertilizer prepared from multi-source solid waste in agricultural applications. The specific steps are as follows:

[0097] (1) Sample preparation: Take the phosphorus-rich functional fertilizer prepared in Example 1, crush it and pass it through a 100-mesh sieve as the sample to be tested.

[0098] (2) Leaching experiment: The leaching method was carried out in accordance with the "Leaching Toxicity of Solid Waste - Horizontal Oscillation Method" (HJ557-2010). 100g of sample was weighed and placed in a 2L extraction bottle, and deionized water was added as the extraction agent at a liquid-to-solid ratio of 10:1 (L / kg).

[0099] (3) Horizontal oscillation: Fix the extraction bottle on a horizontal reciprocating shaker, control the oscillation frequency at 110 times / min and the amplitude at 40 mm at room temperature, oscillate continuously for 8 hours, and then let it stand for 16 hours.

[0100] (4) Precision detection: After leaching, the solution is filtered through a 0.45µm filter membrane. The obtained leachate is analyzed by ICP-MS (inductively coupled plasma mass spectrometry) to determine the precise mass concentration of characteristic heavy metal elements such as chromium (Cr), arsenic (As), lead (Pb), zinc (Zn), and nickel (Ni).

[0101] Table 3 Comparison of heavy metal leaching concentrations and standard limits in phosphorus-enriched functional fertilizers

[0102]

[0103] Experimental verification results:

[0104] Table 3 shows the solidification safety of heavy metals. The experimental results show that the leaching concentrations of each harmful element detected by ICP-MS are extremely low.

[0105] Conclusion and Analysis: This embodiment demonstrates that the 1050℃ high-temperature gradient sintering process employed in this invention allows heavy metals in fly ash and sludge to fully react with aluminosilicates and enter the crystal structure of mullite and anorthite, achieving highly efficient "lattice passivation." Leaching results confirm that this fertilizer exhibits excellent environmental compatibility during its application to the field, fully meeting the safety requirements of ecological agriculture.

[0106] Comparative Example 1

[0107] The steps of this comparative example are basically the same as those of Example 1, except that the Mg-La modified component in step (2) is replaced with an equimolar amount of aluminum component to prepare aluminum-based modified ceramsite rich phosphate fertilizer.

[0108] Test results showed: Decreased adsorption performance: The saturated phosphorus loading of the aluminum-based modified ceramsite was only about 65% of that in Example 1, indicating that the phosphorus capture capacity of the aluminum-based modified layer was significantly weaker than that of the Mg-La bimetallic active layer under the same process conditions; Biotoxicity risk: In seed germination experiments, the group treated with aluminum-based phosphorus-rich fertilizer showed significant growth inhibition. Compared with Example 1, the aluminum-based fertilizer reduced the germination rate of cabbage seeds by 27%. This confirms the view in the literature that aluminum may have toxic effects on plant seedlings, while the Mg-La system used in this invention not only improves fertilizer efficiency but also significantly enhances the germination rate through the synergistic effect of elements.

[0109] Comparative Example 2

[0110] The steps of this comparative example are basically the same as those of Example 1, except that in step (1) "Preparation of fertilizer substrate", the cement used as a binder is replaced with an equal mass of river and lake bottom mud.

[0111] Test results showed that modified ceramsite prepared using river and lake sediment as a binder exhibited a precipitous drop in phosphorus adsorption capacity, with a measured phosphorus adsorption capacity of less than 20 mg / kg. In contrast, ceramsite only demonstrated significant phosphorus adsorption performance when cement was used as a binder, while materials prepared using river and lake sediment or other alternative binders (such as desulfurized gypsum, contaminated soil, etc.) showed almost no effective phosphorus capture capacity. This indicates that cement plays an irreplaceable role in the raw material formulation, providing not only the necessary mechanical binding properties but also the key structural characteristics required for the formation of highly active adsorption sites in ceramsite. Using sediment as a binder prevents the material from achieving nutrient enrichment through subsequent processes, thus failing to meet the production requirements of phosphorus-rich functional fertilizers.

Claims

1. A phosphorus-rich functional fertilizer, characterized in that: The invention includes a porous solid waste ceramic framework, wherein a Mg-La double hydroxide active layer is disposed on the surface of the porous solid waste ceramic framework, and the Mg-La double hydroxide active layer is chemically bonded to a slow-release phosphorus component; the loading of the slow-release phosphorus component is 1481~1511 mg / kg.

2. The phosphorus-enriched functional fertilizer according to claim 1, characterized in that: The slow-release phosphorus component is immobilized on the surface of the active layer in the form of La-P and Mg-OP inner layer complexes. The adsorption behavior of phosphorus by the phosphorus-rich functional fertilizer conforms to the Sips isothermal adsorption model, which has a heterogeneity coefficient of 0.81~0.

83.

3. The phosphorus-enriched functional fertilizer according to claim 1, characterized in that: The porous solid waste ceramic skeleton is made of fly ash, municipal sludge, power plant slag, and cement sintering, and has mullite and anorthite main crystalline phases.

4. The phosphorus-enriched functional fertilizer according to claim 3, characterized in that: The fly ash comprises the following substances in mass percentage: 30-32 wt% Al2O3, 6-7 wt% Fe2O3, 7-8 wt% CaCO3, 1-2 wt% MgO, 1-2 wt% K2O, 1-2 wt% Na2O, with the balance being SiO2.

5. A phosphorus-enriched functional fertilizer according to claim 3, characterized in that: The municipal sludge comprises the following substances by mass percentage: 20-22 wt% Al2O3, 11-12 wt% Fe2O3, 6-7 wt% CaCO3, 2-3 wt% MgO, 2-3 wt% K2O, 0.5-1 wt% Na2O, with the balance being SiO2.

6. The phosphorus-enriched functional fertilizer according to claim 3, characterized in that: The power plant slag comprises the following substances by mass percentage: 36-38 wt% Al2O3, 7-8 wt% Fe2O3, 7-8 wt% CaCO3, 0.5-1 wt% MgO, 0.5-1 wt% K2O, 0.5-1 wt% Na2O, with the balance being SiO2.

7. The phosphorus-enriched functional fertilizer according to claim 3, characterized in that: The cement comprises the following substances in weight percentages: 20-22 wt% SiO2, 6-7 wt% Al2O3, 3-4 wt% Fe2O3, 2-3 wt% MgO, 0.5-1 wt% K2O, 0.1-0.5 wt% Na2O, with the balance being CaCO3.

8. The phosphorus-enriched functional fertilizer according to claim 1, characterized in that: The porous solid waste ceramic skeleton has a porosity ≥ 50.31% and a specific surface area of ​​0.9 × 10⁻⁶. 4 ~1×10 4 cm 2 The average pore size is 5~7nm.

9. A method for preparing a phosphorus-rich functional fertilizer according to any one of claims 1 to 8, characterized in that, Includes the following steps: Fly ash, municipal sludge, power plant slag, and cement are subjected to gradient sintering at 600~1050℃, loaded with an active layer of Mg-La double hydroxide, and then left to stand in a potassium dihydrogen phosphate solution.

10. The application of a phosphorus-rich functional fertilizer according to any one of claims 1 to 8 in slow-release fertilizers or soil conditioners for farmland soil.

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