A solid waste-based porous material for repairing saline-alkali soil and its preparation method and application

Abstract

The present invention relates to the field of soil improvement technology, and more specifically, to a solid waste-based porous material for repairing saline-alkali soil, and its preparation method and application. The raw materials of the solid waste-based porous material include 60-70% coal gangue powder, 24.7-30% phosphogypsum, 5-9.5% functional filler, 0.3-0.5% foaming agent, and a liquid-solid ratio of 0.6-0.7. The present invention effectively improves the problems of insufficient gelling activity of high-silicon-aluminum coal gangue, excessive heavy metal Cd, and the contradiction between porosity and strength of traditional repair materials, achieving multi-target synergy of solid waste resource utilization, heavy metal stabilization and saline-alkali land repair, and providing an industrially feasible path for large-scale saline-alkali land management.

Description

Technical Field

[0001] The present invention relates to the technical field of soil improvement, and more particularly to a solid waste-based porous material for repairing saline-alkali soil, and a preparation method and application thereof. Background Art

[0002] Globally, saline-alkali soils cover 950 million hectares, accounting for 20% of total arable land. Annual agricultural losses due to salinization are estimated at US$27 billion (FAO 2022). my country's saline-alkali land area is approximately 99.13 million hectares, of which approximately 13.33 million hectares are exploitable. Furthermore, the accumulation of industrial solid wastes such as gangue and phosphogypsum exacerbates environmental pressures. China's annual gangue production is approximately 825 million tons, with cumulative stockpiles exceeding 7 billion tons, covering 65,000 hectares. Fifteen percent of these gangue heaps pose a risk of spontaneous combustion (Ministry of Emergency Management 2021), and heavy metals (such as Cd and Pb) exceed permitted levels by over 40%. Annual phosphogypsum production is approximately 80 million tons, with a comprehensive utilization rate of only 45%, and historical stockpiles exceeding 800 million tons (Ministry of Industry and Information Technology 2023). Traditional landfill costs as high as 80-120 yuan per ton.

[0003] Currently, the synergistic utilization of gangue and phosphogypsum (e.g., in cement admixtures and roadbed fill) suffers from low utilization rates (<40%), risks of heavy metal migration, and excessive radioactivity. Therefore, there is an urgent need to develop a highly efficient solid waste resource technology that can increase utilization rates (85-90% for gangue and 70-75% for phosphogypsum) while simultaneously stabilizing heavy metals and optimizing pore structure, thereby promoting the coordinated development of saline-alkali land improvement and solid waste management. Summary of the Invention

[0004] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, one aspect of the present invention is to provide a solid waste-based porous material for repairing saline-alkali soil. The raw materials of the solid waste-based porous material include 60-70% coal gangue powder, 24.7-30% phosphogypsum, 5-9.5% functional filler, 0.3-0.5% foaming agent, and a liquid-solid ratio of 0.6-0.7.

[0005] Preferably, the gangue powder is the gangue from Changcun Coal Mine of Lu'an Mine in Changzhi, Shanxi Province, which has the characteristics of high silicon SiO256%-78%, high aluminum Al2O315%-36%, medium-low calcium and magnesium CaO1.5%-4%, MgO0.62-2.5%, contains 5%-15% organic matter, and has a neutral pH value of 6-9; these components make it have the potential to be used as a soil conditioner; the functional filler is one of perlite, vermiculite and bentonite, and the foaming agent is a composite system of citric acid and calcium carbonate, with a mass ratio of 1:1.2.

[0006] Analysis of coal gangue mineral components

[0007] ‌

[0008] Advantages of silicon and aluminum: 1. SiO2 can improve soil water retention and structural stability and reduce compaction; 2. Al2O3 can promote soil colloid formation and enhance cation exchange capacity (CEC).

[0009] Calcium, magnesium and potassium supplementation: 1. CaO (1.5%-4%) can adjust the pH of acidic soil and improve soil structure; 2. MgO (0.62%-2.5%) is an essential secondary element for plants and can alleviate magnesium deficiency; 3. K2O (1.2%-2.8%) can serve as a slow-release potassium source to supplement soil potassium.

[0010] Organic matter (5%-15%): After composting, it increases the organic carbon content in the soil and promotes microbial activity.

[0011] Another aspect of the present invention is to provide a method for preparing a solid waste-based porous material for repairing saline-alkali soil. The specific steps of the preparation method are as follows:

[0012] S1. Raw material pretreatment: Grind the coal gangue to 100 mesh (150μm) to obtain coal gangue powder; wash, neutralize, and passivate the phosphogypsum, then pass it through a 20-mesh sieve (pore size 0.85mm) to retain particles of 0.1-0.5mm; grind the functional filler;

[0013] S2. quantitatively weighing the pretreated coal gangue powder, phosphogypsum, functional filler and foaming agent according to a proportional distribution;

[0014] S3, complex reaction: mix coal gangue powder with citric acid solution, add 0.2% disodium EDTA, stir at 60℃ for 2 hours, and ensure Al 3+ 、Fe 3+ Complexation rate ≥80%;

[0015] S4, gradient foaming: add calcium carbonate twice to control the CO2 release rate, stir at room temperature for 30 minutes, add 50% for the first time to induce CO2 initial pores, and add the second time to achieve continuous foaming, with the target CO2 gas production ≥200mL / g;

[0016] S5. Solidification and gelling: Add phosphogypsum in batches to avoid Ca 2+ It reacts with citric acid to produce precipitation. In the first stage, 40% of the total amount is added after S3 and before S4 to promote Ca 2+ With SiO3 2- The reaction generates calcium silicate gel (CSH), forming the initial skeleton structure; in the second stage, the remaining 60% is added in the middle of S4 foaming to form a dense gel, and the gelling efficiency is increased by ≥85%. The final product has a porosity of ≥65% and a compressive strength of ≥2.0MPa, which is suitable for saline-alkali soil remediation needs;

[0017] S6, grouting and foaming: pour the obtained gel into a mold and let it stand for 30 minutes to obtain a foamed body;

[0018] S7, gradient pressure curing: The foam obtained in S6 is introduced into CO2 gas and cured at 50°C for the first 24 hours (to accelerate the formation of CSH gel) and then at 35°C for the next 30 hours to obtain a molded foam (to stabilize the pore structure) with a porosity of ≥65% and a compressive strength of ≥2.0 MPa;

[0019] S8, gradient heating and drying: As high-silicon materials are brittle and prone to cracking during drying, the molded foam obtained in S7 is removed from the mold and placed in a 50-120°C oven. The first drying is performed at 50°C for 6 hours to remove surface moisture; the second drying is performed at 80°C for 8 hours, with the heating rate controlled at ≤5°C / hour; and the third drying is performed at 105°C for 4 hours to ensure that the final moisture content is ≤5%, thereby obtaining a dry molded foam.

[0020] S9, uniformly mixing the dried molded foam obtained in S8 with the crushed functional filler;

[0021] S10, granulation: the dried shaped foam obtained in S9 is put into a jaw crusher and crushed to ≤10mm, and then a roller granulator is used to screen 3-5mm particles. The fine powder is recovered by a vibrating screening machine and recycled as a filler. The temperature of the whole process is ≤45℃ to obtain a solid waste-based porous material.

[0022] Preferably, the functional filler in S1 is crushed into 0.5-2 mm, the perlite is crushed into 1.5-2.5 mm, and the bentonite is crushed into <0.075 mm; and the pH of the citric acid in S3 is 3-4.

[0023] Preferably, the two additions of calcium carbonate in S4 are separated by 15 minutes, the first addition of 50% triggers initial CO2 pores, the pH is 4.5-5.0, and the second addition achieves continuous foaming at a pH of 5.5-6.0; in S5, the first stage: high-speed dispersion stirring at 150 rpm for 10 minutes to a pH of 5-6, the temperature is 25 degrees; the second stage: low-speed stirring at 50 rpm (to prevent structural damage) for 5 minutes, the temperature is 50°C, and the pH rises to 7.0-7.5.

[0024] Preferably, the pressure of the CO2 gas introduced in S7 is 0.33 MPa; the aperture of the vibration screening machine in S10 is 3 mm and 5 mm two-stage sieve, and the recovered fine powder is <1 mm.

[0025] Another aspect of the present invention is to provide an application of a solid waste-based porous material for repairing saline-alkali soil, wherein the solid waste-based porous material is used to prepare a soil conditioner.

[0026] Preferably, the soil conditioner comprises a solid waste-based porous material, a functional auxiliary material and a composite bacterial agent.

[0027] Preferably, the functional excipients are woody peat and urea. Woody peat provides a slow-release organic carbon source (organic matter ≥ 60%), promoting microbial colonization. Urea provides a slow-release nitrogen source (≥ 200 mg / kg), maintaining the microbial activity window and preventing nitrogen loss in saline-alkali soils. The composite microbial agent is a mixture of Trichoderma harzianum and Bacillus subtilis.

[0028] Preferably, the solid waste-based porous material and the functional auxiliary material are mixed in a gradient formula according to the degree of land salinization: mild saline-alkali soil: 67%-79% solid waste-based porous material, 20%-30% woody peat, and 1.0%-3.0% urea; moderate saline-alkali soil: 55%-72% solid waste-based porous material, 25%-40% woody peat, and 3.0%-5% urea; severe saline-alkali soil: 50%-66% solid waste-based porous material, 30%-44% woody peat, and 4.0%-6.0% urea; the Trichoderma harzianum liquid and Bacillus subtilis are mixed in a volume ratio of 1:1 and inoculated into the solid waste-based porous material and functional auxiliary material culture medium, the humidity is maintained at 40-60%, the temperature is 25-35°C, and after aerobic culture for 7 days, the culture medium is crushed to a particle size of <2 mm; the viable bacterial count of the Trichoderma harzianum liquid is 1×10 8 spores / mL, the viable bacterial count of the Bacillus subtilis liquid was 8×10 8 Spores / mL.

[0029] The beneficial effects of the present invention are as follows:

[0030] 1. Efficient utilization of solid waste resources, significantly reducing costs

[0031] With industrial solid wastes such as coal gangue (accounting for 60-70%) and phosphogypsum (25-30%) as the main raw materials, the cost is reduced by 50%-60%, and at the same time, large-scale disposal of solid waste resources is achieved (annual disposal capacity can reach 10,000 tons). 2+ The gelation reaction forms CSH gel, which improves the material strength (compression resistance ≥ 2.0MPa) and avoids the defect of easy pulverization of traditional solid waste-based materials.

[0032] 2. The pore structure is controllable, and the efficiency of saline-alkali soil remediation is improved.

[0033] Fractional foaming process: calcium carbonate is added twice, combined with the dual functions of citric acid (foaming agent + heavy metal chelating agent), to achieve CO2 gradient release, increase porosity to 65%-80% (traditional process ≤50%), improve air permeability by 40%, and achieve salt leaching rate ≥30%.

[0034] Gradient curing technology: Through CO2 high pressure (0.33MPa) staged curing (50℃→35℃), it promotes uniform deposition of CaCO3 and improves the uniformity of pore distribution by 25%, adapting to the ventilation requirements of different saline-alkali soil types.

[0035] 3. Long-term stabilization of heavy metals and high environmental safety

[0036] Complexation-solidification dual mechanism: Complexation stage: citric acid (pH 3-4) combined with disodium EDTA (added amount 0.2%), the complexation rate of heavy metals such as Cd and Pb is ≥80% (traditional acid leaching method ≤60%); Solidification stage: CSH gel encapsulates heavy metal ions, and the 28-day leaching toxicity (TCLP) test shows that the Cd dissolution concentration is ≤0.05mg / L (national standard limit 0.1mg / L), and safety is improved by 50%.

[0037] 4. Microorganisms and materials synergize to achieve rapid ecological function recovery

[0038] The adaptability of the composite bacterial agent, Trichoderma harzianum and Bacillus subtilis, is compounded in a 1:1 ratio, which is significantly better than a single bacterial agent in promoting plant growth and stress resistance. The coal gangue amendment requires a higher initial bacterial amount to overcome the pressure of the saline-alkali environment, and the decomposition rate of organic matter is increased by 35%.

[0039] Dynamic regulation of C / N: Woody peat and urea work synergistically to maintain long-term slow-release fertilizer effects, maintain a C / N ratio of 20:1-25:1, increase microbial activity by 50%, and restore soil enzyme (urease, dehydrogenase) activity to 80% of healthy soil.

[0040] 5. The process is highly universal and adaptable to multiple scenarios

[0041] A graded formula system is provided to treat light, medium and heavy saline-alkali soils; it is suitable for industrial production: process optimization such as two-stage screenless crushing and roller granulation reduces energy consumption by 18%, and the fine powder recycling rate is ≥85%, making it suitable for large-scale continuous production.

[0042] 6. Long-term repair effect is stable

[0043] Through the auxiliary addition of perlite, bentonite or vermiculite, the contradiction of traditional pore structure is broken through, the porosity is increased to more than 80% and the compressive strength is ≥2.0MPa, the fluctuation of soil moisture content is reduced by 30%, the vegetation survival rate is increased to, and the soil organic matter content after restoration is steadily increased by ≥2g / kg / year.

[0044] The present invention optimizes the gelling reaction path of solid waste-based raw materials through dynamic citric acid pretreatment and a staged gypsum addition strategy, and prepares a solid waste-based porous material with good performance in combination with gradient pressure curing. The solid waste-based porous material, functional auxiliary materials and composite bacterial agents are compounded to form a solid waste-based soil conditioner with a physical-chemical-biological synergistic repair mechanism. The present invention effectively improves the problems of insufficient gelling activity of high-silicon-aluminum coal gangue, excessive heavy metal Cd, and the contradiction between porosity and strength of traditional repair materials, achieving a multi-target synergy of solid waste resource utilization, heavy metal stabilization and saline-alkali land remediation, and providing an industrially feasible path for large-scale saline-alkali land remediation.

[0045] Additional aspects and advantages of the invention will become apparent from the description which follows, or may be learned by practice of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of the embodiments with reference to the accompanying drawings, in which:

[0047] Figure 1 This is a scanning electron microscope image of a solid waste-based porous material according to Example 1 of the present invention;

[0048] Figure 2 This is a pore size distribution diagram of a solid waste-based porous material according to Example 1 of the present invention;

[0049] Figure 3 This is an XPS spectrum analysis diagram of the solid waste-based porous material in Example 1 of the present invention. DETAILED DESCRIPTION

[0050] In order to more clearly understand the above-mentioned objects, features and advantages of the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be noted that, in the absence of conflict, the embodiments of the present application and the features therein can be combined with each other.

[0051] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from the description. Therefore, the scope of protection of the present invention is not limited to the specific embodiments disclosed below.

[0052] Example 1

[0053] Preparation of solid waste-based porous materials

[0054] S1. Raw material pretreatment: Grind the coal gangue to 100 mesh (150μm) to obtain coal gangue powder; wash, neutralize and passivate the phosphogypsum, then pass it through a 20-mesh sieve (aperture 0.85mm) to retain 0.1-0.5mm particles; grind the perlite to 1.5-2.5mm;

[0055] S2. Quantitatively weigh 65.5% of pretreated coal gangue powder, 28.1% of phosphogypsum, 6% of perlite, and 0.4% of a foaming agent (a composite system of citric acid and calcium carbonate, with a mass ratio of 1:1.2) according to a proportional distribution, with a liquid-to-solid ratio of 0.65;

[0056] S3, complexation reaction: Mix the coal gangue powder with citric acid (pH 3-4) solution, add 0.2% disodium EDTA, stir at 60℃ for 2 hours, and ensure Al 3+ 、Fe 3+ Complexation rate ≥80%;

[0057] S4, gradient foaming: add calcium carbonate twice (15min interval) to control the CO2 release rate, stir at room temperature for 30 minutes, add 50% for the first time to induce CO2 initial pores (pH 4.5-5.0), add the second time to achieve continuous foaming (pH 5.5-6.0), and the target CO2 gas production is ≥200mL / g;

[0058] S5. Solidification and gelling: Add phosphogypsum in batches to avoid Ca 2+ -Citric acid precipitation. In the first stage, 40% of the total amount is added after S3 and before S4 to promote Ca 2+ With SiO3 2- The reaction generates calcium silicate gel (CSH), forming the initial skeleton structure. In the second stage, the remaining 60% is added midway through the S4 foaming process to form a dense gelled network. This increases gelling efficiency by ≥85%, resulting in a final product with a porosity of ≥65% and a compressive strength of ≥2.0 MPa, suitable for saline-alkali soil remediation. Stage 1: Stir at 150 rpm for 10 minutes to a pH of 5-6 at 25°C. Stage 2: Stir at a low speed of 50 rpm for 5 minutes at 50°C to raise the pH to 7.0-7.5.

[0059] S6. Grouting and foaming: pour the obtained slurry into a mold and allow it to foam for 30 minutes to obtain a foamed body.

[0060] S7, gradient pressure curing: The foam obtained in S6 is passed through CO2 gas (pressure 0.33MPa), cured at 50°C for the first 24 hours (to accelerate CSH gel formation), and then at 35°C for the last 30 hours (to stabilize the pore structure). Porosity ≥ 65%, compressive strength ≥ 2.0MPa;

[0061] S8, gradient heating and drying: As high-silicon materials are brittle and prone to cracking during drying, the molded foam obtained in S7 is removed from the mold and placed in a 50-120°C oven. It is dried at 50°C for 6 hours to remove surface moisture; dried at 80°C for 8 hours with a heating rate of ≤5°C / hour; and dried at 105°C for 4 hours to ensure that the final moisture content is ≤5%, thereby obtaining a dry molded foam.

[0062] S9, uniformly mixing the dried molded foam obtained in S8 with the crushed functional filler;

[0063] S10, Granulation: The dried foamed product from S9 is crushed to ≤10mm in a jaw crusher. A roller granulator is then used to sieve 3-5mm particles. The fine powder (<1mm) is recovered and recycled as filler using a vibrating sieving machine (two-stage sieves with apertures of 3mm and 5mm). The entire process is maintained at a temperature of ≤45°C to produce a solid waste-based porous material.

[0064] Comparative Example 1

[0065] Preparation of solid waste-based porous materials

[0066] S1. Raw material pretreatment: Grind the coal gangue to 100 mesh (150μm) to obtain coal gangue powder; wash, neutralize, and passivate the phosphogypsum, then pass it through a 20-mesh sieve (pore size 0.85mm), retaining particles of 0.1-0.5mm;

[0067] S2. Quantitatively weigh 70% of pretreated coal gangue powder, 29.6% of phosphogypsum, and 0.4% of a foaming agent (a composite system of citric acid and calcium carbonate, with a mass ratio of 1:1.2) according to a proportional distribution, with a liquid-to-solid ratio of 0.65;

[0068] S3, complexation reaction: Mix the coal gangue powder with citric acid (pH 3-4) solution, add 0.2% disodium EDTA, stir at 60℃ for 2 hours, and ensure Al 3+ 、Fe 3+ Complexation rate ≥80%;

[0069] S4, gradient foaming: add calcium carbonate twice (15min interval) to control the CO2 release rate, stir at room temperature for 30 minutes, add 50% for the first time to induce CO2 initial pores (pH 4.5-5.0), add the second time to achieve continuous foaming (pH 5.5-6.0), and the target CO2 gas production is ≥200mL / g;

[0070] S5. Solidification and gelling: Add phosphogypsum in batches to avoid Ca 2+ -Citric acid precipitation. In the first stage, 40% of the total amount is added after S3 and before S4 to promote Ca 2+ With SiO3 2- The reaction generates calcium silicate gel (CSH), forming the initial skeleton structure. In the second stage, the remaining 60% is added midway through the S4 foaming process to form a dense gelled network. This increases gelling efficiency by ≥85%, resulting in a final product with a porosity of ≥65% and a compressive strength of ≥2.0 MPa, suitable for saline-alkali soil remediation. Stage 1: Stir at 150 rpm for 10 minutes to a pH of 5-6 at 25°C. Stage 2: Stir at a low speed of 50 rpm for 5 minutes at 50°C to raise the pH to 7.0-7.5.

[0071] S6. Grouting and foaming: pour the obtained slurry into a mold and allow it to foam for 30 minutes to obtain a foamed body.

[0072] S7, gradient pressure curing: The foam obtained in S6 is passed through CO2 gas (pressure 0.33MPa), cured at 50°C for the first 24 hours (to accelerate CSH gel formation), and then at 35°C for the last 30 hours (to stabilize the pore structure). Porosity ≥ 65%, compressive strength ≥ 2.0MPa;

[0073] S8, gradient heating and drying: As high-silicon materials are brittle and prone to cracking during drying, the molded foam obtained in S7 is removed from the mold and placed in a 50-120°C oven. It is dried at 50°C for 6 hours to remove surface moisture; dried at 80°C for 8 hours with a heating rate of ≤5°C / hour; and dried at 105°C for 4 hours to ensure that the final moisture content is ≤5%, thereby obtaining a dry molded foam.

[0074] S9, Granulation: The dried foam obtained in S8 is crushed in a jaw crusher to ≤10mm. A roller granulator is then used to sieve 3-5mm particles. The fine powder (<1mm) is recovered and recycled as filler using a vibrating sieving machine (two-stage sieves with apertures of 3mm and 5mm). The entire process is maintained at a temperature of ≤45°C to produce a solid waste-based porous material.

[0075] Then, referring to the methods of Examples 2 to 3, a solid waste-based soil conditioner was prepared.

[0076] Comparative Example 2

[0077] Commonly used soil conditioners in the prior art

[0078] The ingredients of the existing solid waste-based porous soil conditioner are: 20-30 parts of coal gangue powder, 40-50 parts of organic acid, 3-4 parts of potassium humate, 5-10 parts of urea, 2-10 parts of diammonium hydrogen phosphate and 10-15 parts of biochemical humic acid, calculated by mass.

[0079] The performance of the coal-based solid waste porous materials of Example 1, Comparative Example 1 and Comparative Example 2 are compared and analyzed, and the results are shown in Table 1 below.

[0080] Table 1. Performance analysis results of Example 1, Comparative Example 1 and Comparative Example 2

[0081]

[0082] The solid waste-based porous material of Example 1 was compared with Comparative Examples 1 and 2 in four aspects: From the perspective of pore size distribution, the bimodal type in Example 1 breaks through the traditional single-peak / irregular distribution, achieving a synergistic effect of rapid water conduction through large pores (40% increase in permeability within 30 seconds) and long-term water retention through micropores (water retention rate >80% after 180 days). From the perspective of water absorption performance, the water absorption rate of 185% is 54.2% higher than that of commercial products, the pore connectivity is increased to 0.78 (traditional materials <0.5), and the water molecule diffusion coefficient reaches 2.3×10 -6 m 2 / s. Regarding heavy metal fixation, the Cd / Pb fixation rate exceeded the 99% threshold. XPS binding energy analysis revealed that the Cd-O bond (406.8 eV) and the Pb-P bond (138.5 eV) formed a stable lattice structure. Regarding pH buffering, the CaCO3 / silicate slow-release system achieved dynamic pH balance, extending the effective duration of action by three times compared to commercial products.

[0083] Innovation point evidence: Example 1: Bimodal pore size distribution of solid waste-based porous materials (such as Figure 1 、 2 As shown in the figure) to achieve rapid water absorption (macropores) and long-term water retention (micropores) synergistically; by XPS analysis (as shown in the figure) Figure 3 (as shown) confirmed that heavy metals existed in a stable state of CdSiO3 / Pb3(PO4)2.

[0084] 1. Cd chemical state analysis

[0085] The Cd 3d5 / 2 binding energy is located at 406.8 eV, which corresponds to the formation of Cd-O bonds, indicating that Cd is stably fixed through oxygen coordination bonds.

[0086] Compared with the standard CdO reference value (405.0 eV), the binding energy has a positive shift of 1.8 eV, indicating the existence of a stronger electron cloud polarization effect in the lattice structure.

[0087] 2. Pb chemical state analysis

[0088] The Pb4f7 / 2 peak appears at 138.5 eV, which is 0.6 eV negatively shifted compared with metal sulfides (137.9 eV of PbS), confirming the unique coordination environment of the Pb-P bond.

[0089] No characteristic peak of Pb-0 (~137 eV) was detected, and the interference of oxides was ruled out.

[0090] Example 2

[0091] Preparation of solid waste-based soil conditioner using solid waste-based porous material prepared in embodiment 1

[0092] The solid waste-based porous material prepared in Example 1 and functional auxiliary materials (woody peat and urea) were mixed in a gradient formula according to the degree of land salinization. After mixing, a composite bacterial agent was added at a total weight of 2-3%. The mixture was aerobically fermented for 7-10 days (temperature 30-40°C, turning frequency 3 days / time) to prepare a solid waste-based soil conditioning agent.

[0093] Mild saline-alkali soil: solid waste-based porous materials 67%-79%, woody peat 20%-30%, urea 1.0%-3.0%; moderate saline-alkali soil: solid waste-based porous materials 55%-72%, woody peat 25%-40%, urea 3.0%-5%; severe saline-alkali soil: solid waste-based porous materials 50%-66%, woody peat 30%-44%, urea 4.0%-6.0%.

[0094] The woody peat raw material is physically crushed by a high-speed shearing machine to a particle size not exceeding 1 mm to obtain woody peat powder.

[0095] Depending on the degree of soil salinization, it is recommended to add 200-500 kg of solid waste-based soil adjustment per mu, regularly test the soil EC value (electrical conductivity), pH and C / N ratio, and adjust subsequent topdressing strategies.

[0096] The two bacterial liquids were activated and cultured with Trichoderma harzianum and Bacillus subtilis, mixed at a volume ratio of 1:1, added with sterile distilled water containing 0.1% Tween 80, and shaken to obtain a composite bacterial liquid. The mixture was inoculated into a solid waste-based porous material culture medium containing 10%-15% woody peat, with the humidity maintained at 40-60% and the temperature at 25-35°C. After aerobic culture for 7 days, the mixture was crushed to a particle size of <2 mm. The obtained bacterial agent was inoculated into a new culture medium at a ratio of 10-15%, and the culture was expanded 2-3 times to obtain a total viable bacterial count of ≥2×10 8 CFU / g of composite bacterial agent.

[0097] Trichoderma harzianum was inoculated into PDA solid medium and cultured at 25-30°C for 7 days until the colonies produced spores; Bacillus subtilis was inoculated into LB liquid medium and cultured in a shaking incubator at 35-37°C for 24 hours until the OD600 value reached 0.8-1.0. The viable cell count of Trichoderma harzianum liquid was 1×10 8 spores / mL, the viable bacterial count of the Bacillus subtilis liquid was 8×10 8 Spores / mL.

[0098] Trichoderma harzianum secretes extracellular polysaccharides to promote the formation of soil aggregates, and the efficiency of phosphorus and potassium solubilization is increased by 40%; Bacillus subtilis produces organic acids to passivate heavy metals (Cd / Pb / Cr passivation rate ≥85%), while inhibiting the proliferation of pathogens. The composite bacterial agent is significantly superior to a single bacterial agent in promoting plant growth and stress resistance, and the coal gangue amendment requires a higher initial bacterial amount to overcome the pressure of the saline-alkali environment.

[0099] Example 3

[0100] Using the solid waste-based soil conditioner prepared in Example 2 to act on saline-alkali land ecological restoration

[0101] Soil pretreatment: Plough the saline-alkali land (depth 20-30cm) to break up large soil blocks and increase air permeability; apply a mixture of porous materials and woody peat, and mechanically plow and mix thoroughly; if the pH is > 9.5 or the salt content is > 10g / kg, leaching and salt reduction must be carried out in advance (EC value of leaching water ≤ 1.5mS / cm).

[0102] Mix the improver: microbial agent: water at a ratio of 100:2-3:80-100 (mass ratio). Maintain a temperature of 15-35°C, humidity ≥ 60%, avoid direct sunlight, and maintain a wind speed ≤ Level 4 to prevent the microbial agent from dispersing.

[0103] Spray seeding operation: Bottom layer spraying: first spray the mixture of bacterial amendments (thickness 5-8cm) to promote microbial colonization; surface covering: cover with humus soil or planting soil (thickness 3-5cm) to protect the microbial community; seed / vegetation layer: sow salt-alkali tolerant plant seeds (such as sea buckthorn and alkali sedge), and cover with soil thickness 1-2cm.

[0104] Spraying operation parameters: spraying rate 20-30m³ / h, moisture content: the moisture content of the mixed liquid is controlled at 40%-50%, pH adjustment: real-time monitoring after spraying, and adding citric acid if necessary (maintain pH 6.0-7.0).

[0105] Post-construction management

[0106] Moisturizing maintenance: Cover with non-woven fabric or straw (light transmittance ≤ 30%) immediately after spraying to reduce water evaporation; spray water regularly (twice a day in the initial stage, for 15 days) to maintain soil moisture content ≥ 20%.

[0107] Microbial activity monitoring: Soil samples (0-20 cm depth) were collected regularly to detect the number of microorganisms (total colony count ≥ 1×10 7 CFU / g); monitor soil enzyme activities (such as urease and dehydrogenase) and evaluate the recovery of microbial functions.

[0108] Dynamic regulation: If the EC value is >2mS / cm or pH>8.5, spray the amendment containing woody peat; in areas with severe salinity and alkali stress, add a drip irrigation system to supplement the bacterial solution (concentration diluted to 1×10 6 CFU / mL).

[0109] The solid waste-based soil conditioner prepared by the present invention was applied to soils of different saline-alkali land types and compared with the untreated control area (p<0.01, t-test) to observe the application effect. The saturated extraction method (USDA method) was used to determine the salt content, and the results are shown in Table 2 below.

[0110] Table 2. Comparison of soil changes after applying solid waste-based soil conditioners in different geological conditions

[0111]

[0112] Applying the solid waste-based soil conditioner to chloride-, sulfate-, and soda-alkalized soils reduced EC values, meeting the secondary farmland standard, and increased crop yields and microbial diversity. This demonstrates that applying the solid waste-based soil conditioner prepared in this application to different saline-alkali soil types has achieved a triple breakthrough: improving the physical structure, optimizing chemical properties, and reestablishing biological functions in saline-alkali land.

[0113] The solid waste-based soil conditioner prepared in this application was applied to the saline-alkali area of ​​the Inner Mongolia project. The tracking data for five consecutive years are shown in Table 3 below:

[0114] Table 3. Comparison of soil changes in saline-alkali areas after application of solid waste-based soil conditioners for five consecutive years

[0115]

[0116] As shown in Table 3, the soil alkalinity (ESP) continued to decrease: the initial ESP was 21.4% and decreased to 7.1% in the fifth year. 2+ Replacement of Na adsorbed by soil colloids + , reducing the sodium adsorption ratio (SAR); the ESP in the fifth year still maintained a downward trend, indicating that the slow-release calcium source (such as phosphogypsum) in the conditioner continued to release Ca 2+ , inhibiting the return of sodium salt. Organic matter and microbial biomass carbon increased significantly: organic matter increased from 3.8g / kg to 9.5g / kg: solid waste-based porous materials contain more pores to adsorb organic humic acid; at the same time, auxiliary materials such as woody peat provide exogenous organic carbon. Microbial biomass carbon increased by 349%: the porous structure improves soil permeability and promotes the reproduction of aerobic microorganisms; the decomposition of organic matter releases carbon sources and activates functional bacteria (such as Bacillus subtilis). Corn yield increased in a step-by-step manner: the yield increased from 1.2t / ha to 6.2t / ha: ESP reduction alleviates sodium toxicity and promotes root absorption of nutrients; enhanced microbial activity improves the release efficiency of nutrients in solid waste-based soil conditioners.

[0117] For coastal chloride saline-alkali soils, a solid waste-based conditioner formulation consisting of 57% solid waste-based porous material, 38% woody peat, and 5% urea is used. Till the saline-alkali soil (to a depth of 20-30 cm) to break up large soil clumps and increase air permeability. Then, mechanically till and mix 3.5 t / ha of porous material, 2.3 t / ha of woody peat, and 0.3 t / ha of urea. If the pH is >9.5 or the salt content is >10 g / kg, pre-rinse to reduce salinity (leach water EC value ≤ 1.5 mS / cm). Mix the solid waste-based porous material conditioner: bacterial agent: water at a mass ratio of 100:2-3:80-100. Spray seed the saline-alkali soil in need of treatment. Immediately cover with non-woven fabric or straw (light transmittance ≤ 30%) to reduce evaporation. Regularly spray water (twice daily for the initial 15 days) to maintain a soil moisture content ≥20%.

[0118] The results showed that: 30 days Cl - The leaching rate was 68.5% (control group: 22.3%), soil aggregates (>0.25 mm) increased to 41.7% (initial 12.5%), and real-time PCR analysis showed a 4.2-fold increase in the copy number of functional genes (such as nifH). The application of this solid waste-based soil conditioner achieved efficient desalination, structural improvement, and ecological function restoration of coastal saline-alkali soils. - The leaching rate, aggregate stability, and microbial activity data all outperformed those of traditional amendments. Future field-scale validation and process parameter optimization will further enhance its application value in coastal saline-alkali areas.

[0119] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that the present invention is susceptible to various modifications and variations. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for preparing a solid waste-based porous material for repairing saline-alkali soil, characterized by: The raw materials of the solid waste-based porous material include 60-70% coal gangue powder, 24.7-30% phosphogypsum, 5-9.5% functional filler, 0.3-0.5% foaming agent, and a liquid-to-solid ratio of 0.6-0.7; The gangue powder is gangue from the Changcun Coal Mine in Lu'an Mine, Changzhi, Shanxi Province. It has the characteristics of high silicon SiO2 56%-78%, high aluminum Al2O3 15%-36%, medium-low calcium and magnesium CaO 1.5%-4%, and MgO 0.62-2.5%. It contains 5%-15% organic matter and has a neutral pH value of 6-9. The functional filler is one of perlite, vermiculite, and bentonite. The foaming agent is a composite system of citric acid and calcium carbonate, with a mass ratio of 1:1.

2. The specific steps of the preparation method are as follows: S1. Raw material pretreatment: Grind the coal gangue to 100 mesh to obtain coal gangue powder; wash, neutralize, and passivate the phosphogypsum, then pass it through a 20-mesh sieve to retain 0.1-0.5mm particles; grind the functional filler; S2. quantitatively weighing the pretreated coal gangue powder, phosphogypsum, functional filler and foaming agent according to a proportional distribution; S3, complex reaction: mix coal gangue powder with citric acid solution, add 0.2% disodium EDTA, stir at 60℃ for 2 hours, and ensure Al 3+ 、Fe 3+ Complexation rate ≥80%; S4, gradient foaming: add calcium carbonate twice to control the CO2 release rate, stir at room temperature for 30 minutes, add 50% for the first time to induce CO2 initial pores, and add the second time to achieve continuous foaming, with the target CO2 gas production ≥200mL / g; S5. Solidification and gelling: Add phosphogypsum in batches to avoid Ca 2+ It reacts with citric acid to produce precipitation. In the first stage, 40% of the total amount is added after S3 and before S4 to promote Ca 2+ With SiO3 2- The reaction generates calcium silicate gel (CSH), forming the initial skeleton structure; in the second stage, the remaining 60% is added in the middle of S4 foaming to form a dense gel; S6, grouting and foaming: pour the obtained gel into a mold and let it stand for 30 minutes to obtain a foamed body; S7, gradient pressure curing: the foam obtained in S6 is introduced into CO2 gas, cured at 50°C for the first 24 hours and then at 35°C for the next 30 hours to obtain a molded foam; S8, gradient heating and drying: the molded foam obtained in S7 is removed from the mold and placed in a 50-120°C oven, first dried at 50°C for 6 hours to remove surface moisture; second dried at 80°C for 8 hours, controlling the heating rate to be ≤5°C / hour; and third dried at 105°C for 4 hours, ensuring that the final moisture content is ≤5%, to obtain a dry molded foam; S9, uniformly mixing the dried molded foam obtained in S8 with the crushed functional filler; S10, granulation: the dried shaped foam obtained in S9 is put into a jaw crusher and crushed to ≤10mm, and then a roller granulator is used to screen 3-5mm particles. The fine powder is recovered by a vibrating screening machine and recycled as a filler. The temperature of the whole process is ≤45℃ to obtain a solid waste-based porous material.

2. The method for preparing a solid waste-based porous material for repairing saline-alkali soil according to claim 1, characterized in that: The functional filler in S1 is crushed into 0.5-2 mm, perlite is crushed into 1.5-2.5 mm, and bentonite is crushed into less than 0.075 mm; the pH of the citric acid in S3 is 3-4.

3. The method for preparing a solid waste-based porous material for repairing saline-alkali soil according to claim 1, characterized in that: In the S4, the interval between the two additions of calcium carbonate is 15 minutes. The first addition of 50% triggers the initial pores of CO2, and the pH is 4.5-5.

0. The second addition achieves continuous foaming and the pH is 5.5-6.

0. In the S5, the first stage: high-speed dispersion stirring at 150 rpm for 10 minutes to pH 5-6, the temperature is 25 degrees; the second stage: low-speed stirring at 50 rpm for 5 minutes, the temperature is 50°C, and the pH rises to 7.0-7.

5.

4. The method for preparing a solid waste-based porous material for repairing saline-alkali soil according to claim 1, characterized in that: The pressure of CO2 gas introduced into S7 is 0.33 MPa; the aperture of the vibration screening machine in S10 is 3mm and 5mm, and the recovered fine powder is less than 1mm.

5. The use of the porous material for repairing saline-alkali soil solid waste prepared by the method according to claim 1, characterized in that: The solid waste-based porous material is used to prepare a soil conditioner.

6. The use of the porous material for repairing saline-alkali soil solid waste prepared by the method according to claim 5, characterized in that: The soil conditioner comprises a solid waste-based porous material, a functional auxiliary material and a composite bacterial agent.

7. The use of the porous material for repairing saline-alkali soil solid waste prepared by the method according to claim 6, characterized in that: The functional auxiliary materials are woody peat and urea, and the composite bacterial agent is a mixture of Trichoderma harzianum and Bacillus subtilis.

8. The use of the porous material for repairing saline-alkali soil solid waste prepared by the method according to claim 7, characterized in that: The solid waste-based porous material and the functional auxiliary material are mixed in a gradient formula according to the degree of land salinization: mild saline-alkali soil: 67%-79% solid waste-based porous material, 20%-30% woody peat, and 1.0%-3.0% urea; moderate saline-alkali soil: 55%-72% solid waste-based porous material, 25%-40% woody peat, and 3.0%-5% urea; severe saline-alkali soil: 50%-66% solid waste-based porous material, 30%-44% woody peat, and 4.0%-6.0% urea; the Trichoderma harzianum liquid and the Bacillus subtilis liquid are mixed in a volume ratio of 1:1, inoculated into the solid waste-based porous material and functional auxiliary material culture medium, the humidity is maintained at 40-60%, the temperature is 25-35°C, and after aerobic culture for 7 days, the culture medium is crushed to a particle size of <2 mm; the viable bacterial count of the Trichoderma harzianum liquid is 1×10 8 spores / mL, the viable bacterial count of the Bacillus subtilis liquid was 8×10 8 Spores / mL.

Images