Solid-waste-based porous material for repairing saline-alkali soil as well as preparation method and application of solid-waste-based porous material

Abstract

The invention relates to the technical field of soil improvement, in particular to a solid-waste-based porous material for repairing saline-alkali soil and a preparation method and application of the solid-waste-based porous material. The solid waste-based porous material is prepared from the following raw materials: 60 to 70 percent of coal gangue powder, 24.7 to 30 percent of phosphogypsum, 5 to 9.5 percent of functional filler and 0.3 to 0.5 percent of foaming agent, and the liquid-solid ratio is 0.6 to 0.7. According to the invention, the problems of insufficient gelation activity of high-silicon-aluminum coal gangue, excessive heavy metal Cd, contradiction between pores and strength of a traditional repair material and the like are effectively improved, multi-target coordination of solid waste recycling, heavy metal stabilization and saline-alkali soil repair is realized, and an industrial feasible path is provided for large-scale saline-alkali soil treatment.

Description

Technical Field

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

[0002] The global area of saline-alkali soil reaches 950 million hectares, accounting for 20% of the total cultivated land area. The annual agricultural loss caused by salinization is about 27 billion US dollars (FAO 2022). The area of saline-alkali land in China is about 99.13 million hectares, of which the exploitable area is about 13.33 million hectares. At the same time, the accumulation of industrial solid wastes such as coal gangue and phosphogypsum has increased the environmental pressure. The annual output of coal gangue in China is about 825 million tons, and the cumulative stockpile exceeds 7 billion tons, occupying 65,000 hectares of land. Among them, 15% of the coal gangue mountains are at risk of spontaneous combustion (Emergency Management Department 2021), and the heavy metal (such as Cd, Pb) exceeding standard rate > 40%. The annual output of phosphogypsum is about 80 million tons, and the comprehensive utilization rate is only 45%. The historical stockpile exceeds 800 million tons (Ministry of Industry and Information Technology 2023), and the traditional landfill cost is as high as 80 - 120 yuan / ton.

[0003] At present, the co-utilization technologies of coal gangue and phosphogypsum (such as cement admixture, subgrade filling) have problems such as low utilization rate (<40%), heavy metal migration risk and radioactivity exceeding the standard. Therefore, it is urgent to develop an efficient solid waste resource utilization technology to promote the coordinated development of saline-alkali land improvement and solid waste treatment while improving the utilization rate (85 - 90% for coal gangue, 70 - 75% for phosphogypsum), realizing heavy metal stabilization and pore structure optimization. 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, an object of 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 the liquid-solid ratio is 0.6 - 0.7.

[0005] Preferably, the coal gangue powder is from Changcun Coal Mine of Lu'an Mine in Changzhi, Shanxi. It has the characteristics of high silicon SiO₂ 56% - 78%, high aluminum Al₂O₃ 15% - 36%, medium and low calcium and magnesium CaO 1.5% - 4%, MgO 0.62 - 2.5%, contains 5% - 15% organic matter, and the pH value is 6 - 9, showing neutrality; 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 Mineral Components of Coal Gangue Advantages of silicon and aluminum: 1. SiO2 can improve soil water retention and structural stability, reducing soil compaction; 2. Al2O3 can promote the formation of soil colloids and enhance cation exchange capacity (CEC).

[0007] Supplementation of calcium, magnesium and potassium: 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 medium element for plants and can alleviate magnesium deficiency; 3. K2O (1.2%-2.8%) can be used as a slow-release potassium source to supplement soil potassium.

[0008] Organic matter (5%-15%): After being decomposed, it can increase the soil organic carbon content and promote microbial activity.

[0009] Another object of this invention is to provide a preparation method of a solid waste-based porous material for repairing saline-alkali soil. The specific steps of the preparation method are as follows: S1. Raw material pretreatment: The coal gangue is crushed to 100 mesh (150μm) to obtain coal gangue powder; the phosphogypsum is washed, neutralized, passivated and then sieved through a 20-mesh sieve (pore diameter 0.85mm), and particles with a size of 0.1-0.5mm are retained; the functional filler is crushed. S2. Weigh the pretreated coal gangue powder, phosphogypsum, functional filler and foaming agent according to the proportional distribution and quantification. S3. Complexation reaction: The coal gangue powder is mixed with a citric acid solution, 0.2% disodium EDTA is added, and it is stirred at 60°C for 2 hours to ensure that the complexation rate of Al 3+ , Fe 3+ ≥80%. S4. Gradient foaming: Calcium carbonate is added in two batches to control the CO2 release rate, stirred at room temperature for 30 minutes. 50% is added for the first time to initiate the initial pores of CO2, and the second addition realizes continuous foaming. The target gas production of CO2 ≥ 200 mL / g. S5. Solidification and gelling: Phosphogypsum is added in batches to avoid precipitation caused by the reaction of Ca 2+ with citric acid. 40% of the total amount is added after S3 and before S4 in the first stage to promote the reaction of Ca 2+ with SiO3 2- to generate calcium silicate gel (C-S-H), forming an initial skeleton structure; 60% of the remainder is added in the middle stage of S4 foaming in the second stage to form a dense gel, and the gelling efficiency is increased by ≥85%. The final product has a porosity ≥ 65% and a compressive strength ≥ 2.0 MPa, meeting the requirements for saline-alkali soil repair. S6. Grouting and foaming: Pour the obtained gel into a mold and let it stand and foam for 30 min to obtain a foam body. S7. Gradient pressure curing: Introduce the foam obtained in S6 into CO2 gas, cure it at 50°C for the first 24 hours (to accelerate the formation of C-S-H gel), and then cure it at 35°C for the next 30 hours to obtain the formed foam (to stabilize the pore structure), with a porosity ≥ 65% and a compressive strength ≥ 2.0 MPa; S8. Gradient temperature drying: Since high-silica materials are brittle and prone to cracking during drying, remove the formed foam obtained in S7 from the mold and place it in an oven at 50 - 120°C. Dry it at 50°C for 6 hours for the first time to remove surface moisture; dry it at 80°C for 8 hours for the second time, controlling the heating rate ≤ 5°C / hour; dry it at 105°C for 4 hours for the third time to ensure that the final water content ≤ 5%, obtaining the dried formed foam; S9. Uniformly mix the dried formed foam obtained in S8 with the crushed functional filler; S10. Granulation: Put the dried formed foam obtained in S9 into a jaw crusher and crush it to ≤ 10 mm, then use a roller granulator to screen 3 - 5 mm particles, and recycle the fine powder as filler through a vibrating screen, with the whole process temperature ≤ 45°C, to obtain the solid waste-based porous material.

[0010] Preferably, in S1, the functional filler is crushed specifically as follows: vermiculite is crushed to 0.5 - 2 mm, perlite is crushed to 1.5 - 2.5 mm, and bentonite is pulverized to < 0.075 mm; in S3, the citric acid has a pH of 3 - 4.

[0011] Preferably, in S4, the time interval between the two additions of calcium carbonate is 15 min. The first addition of 50% initiates the initial pores of CO2, with a pH of 4.5 - 5.0, and the second addition realizes continuous foaming with a pH of 5.5 - 6.0; in S5, the first stage: disperse and stir at a high speed of 150 rpm for 10 minutes until the pH is 5 - 6 and the temperature is 25°C; the second stage: stir at a low speed of 50 rpm (to prevent structure damage) for 5 minutes, with a temperature of 50°C and the pH rising to 7.0 - 7.5.

[0012] Preferably, in S7, the pressure of the CO2 gas introduced is 0.33 MPa; in S10, the vibrating screen has two-stage meshes with apertures of 3 mm and 5 mm, and the recycled fine powder is < 1 mm.

[0013] Another object of the present invention is to provide an application of the solid waste-based porous material for repairing saline-alkali soil, and the application of the solid waste-based porous material for preparing a soil conditioner.

[0014] Preferably, the soil conditioner includes a solid waste-based porous material, a functional auxiliary material, and a compound bacterial agent.

[0015] Preferably, the functional auxiliary materials are woody peat and urea. The woody peat provides a slow-release organic carbon source (organic matter ≥ 60%) to promote the colonization of microorganisms. Urea provides slow-release nitrogen (≥ 200 mg / kg) to maintain the active window period of microorganisms and avoid nitrogen loss in saline-alkali soil. The compound microbial agent is a mixture of Trichoderma harzianum and Bacillus subtilis.

[0016] Preferably, the solid waste-based porous material and the functional auxiliary materials are mixed according to a gradient formula set according to the degree of soil salinization. For slightly saline-alkali soil: 67%-79% of the solid waste-based porous material, 20%-30% of woody peat, and 1.0%-3.0% of urea; for moderately saline-alkali soil: 55%-72% of the solid waste-based porous material, 25%-40% of woody peat, and 3.0%-5% of urea; for severely saline-alkali soil: 50%-66% of the solid waste-based porous material, 30%-44% of woody peat, and 4.0%-6.0% of urea. The Trichoderma harzianum liquid and Bacillus subtilis are mixed at a volume ratio of 1:1 and inoculated into the medium of the solid waste-based porous material and the functional auxiliary materials. The humidity is maintained at 40-60%, the temperature is 25-35°C, and after aerobic cultivation for 7 days, it is crushed to a particle size of < 2 mm. The viable count of the Trichoderma harzianum liquid is 1×10 8 spores / mL, and the viable count of the Bacillus subtilis liquid is 8×10 8 spores / mL.

[0017] The beneficial effects of the present invention are as follows: 1. High-efficient utilization of solid waste resources and significant cost reduction Using 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%. At the same time, large-scale disposal of solid waste resources is realized (the annual consumption can reach the ten-thousand-ton level). Through the gelation reaction of SiO2 in coal gangue and Ca 2+ in phosphogypsum to form C-S-H gel, the strength of the material is improved (compressive strength ≥ 2.0 MPa), avoiding the defect of easy powdering of traditional solid waste-based materials.

[0018] 2. Controllable pore structure and improved efficiency of saline-alkali soil remediation Graded foaming process: Calcium carbonate is added in two steps, combined with the dual functions of citric acid (foaming agent + heavy metal chelating agent), to achieve a gradient release of CO2. The porosity is increased to 65%-80% (traditional process ≤ 50%), the air permeability is improved by 40%, and the salt leaching rate is ≥ 30%.

[0019] Gradient curing technology: Through high-pressure CO2 (0.33 MPa) staged curing (50°C → 35°C), it promotes the uniform deposition of CaCO3, and the uniformity of pore distribution is improved by 25%, adapting to the air permeability requirements of different types of saline-alkali soil.

[0020] 3. Long-term and stable heavy metal stabilization, high environmental safety Complexation-solidification dual mechanism: Complexation stage: Citric acid (pH 3-4) combined with disodium EDTA (addition amount 0.2%) has a complexation rate of ≥80% for heavy metals such as Cd and Pb (≤60% for the traditional acid leaching method); Solidification stage: C-S-H gel coats heavy metal ions. The toxicity characteristic leaching procedure (TCLP) test after 28 days shows that the dissolved concentration of Cd ≤ 0.05 mg / L (national standard limit 0.1 mg / L), and the safety is improved by 50%.

[0021] 4. Microbe-material synergistic effect, rapid restoration of ecological functions Compatibility of compound microbial agents: Trichoderma harzianum and Bacillus subtilis are compounded at a ratio of 1:1, which is significantly superior to single microbial agents in promoting plant growth and stress resistance. And the coal gangue modifier requires a relatively high initial microbial agent amount to overcome the stress of the saline-alkali environment, and the organic matter decomposition rate is increased by 35%.

[0022] Dynamic regulation of C / N: Woody peat and urea act synergistically to maintain long-term slow-release fertilizer efficiency, maintain a C / N ratio of 20:1 - 25:1, the microbial activity is increased by 50%, and the activities of soil enzymes (urease, dehydrogenase) are restored to 80% of healthy soil.

[0023] 5. Strong process universality, suitable for multiple scenarios Provide a grading formula system for treating light, medium, and heavy saline-alkali soils; Adaptation for industrial production: Optimization of processes such as double-stage sieve-free crushing and roll granulation reduces energy consumption by 18%, and the recycling rate of fine powder ≥ 85%, suitable for large-scale continuous production.

[0024] 6. Stable long-term repair effect Through the auxiliary addition of perlite, bentonite or vermiculite, the contradiction of the traditional pore structure is broken through. The porosity is increased to more than 80% and the compressive strength ≥ 2.0 MPa. The fluctuation of soil moisture content is reduced by 30%, the vegetation survival rate is increased to, and the organic matter content in the soil after repair is stably increased by ≥ 2 g / kg / year.

[0025] This invention optimizes the gelling reaction path by dynamically pretreating solid waste-based raw materials with citric acid and adding gypsum in stages, and combines gradient pressure curing to prepare a solid waste-based porous material with good performance. The solid waste-based porous material, functional auxiliary materials and compound microbial agents are compounded to form a solid waste-based soil conditioner with a physical-chemical-biological synergistic repair mechanism. This invention effectively improves problems such as insufficient gelling activity of high-silicon-aluminum coal gangue, excessive heavy metal Cd, and the contradiction between pores and strength of traditional repair materials, realizes the multi-objective coordination of solid waste resource utilization, heavy metal stabilization and saline-alkali land restoration, and provides an industrially feasible path for large-scale saline-alkali land treatment.

[0026] Additional aspects and advantages of the present invention will become apparent in the following description or be learned through the practice of the present invention. Brief Description of the Drawings

[0027] The above and / or additional aspects and advantages of the present invention will become apparent and be readily understood from the description of the embodiments in conjunction with the following drawings, in which: Figure 1 is a scanning electron microscope image of the solid waste-based porous material in the first embodiment of the present invention; Figure 2 is a pore size distribution diagram of the solid waste-based porous material in the first embodiment of the present invention; Figure 3 is an XPS spectrum analysis diagram of the solid waste-based porous material in the first embodiment of the present invention. Detailed Embodiments

[0028] In order to more clearly understand the above objects, features and advantages of the present invention, the present invention will be further described in detail below in conjunction with the drawings and specific embodiments. It should be noted that, without conflict, the embodiments of the present application and the features in the embodiments may be combined with each other.

[0029] In the following description, many specific details are set forth in order to fully understand the present invention. However, the present invention may also be implemented in other ways different from those described herein. Therefore, the protection scope of the present invention is not limited by the specific embodiments disclosed below.

[0030] First Embodiment Preparation of Solid Waste-Based Porous Material S1. Raw material pretreatment: Coal gangue is crushed to 100 mesh (150 μm) to obtain coal gangue powder; Phosphogypsum is washed with water, neutralized, passivated and then sieved through a 20-mesh sieve (pore size 0.85 mm), and particles with a size of 0.1 - 0.5 mm are retained; Perlite is crushed to 1.5 - 2.5 mm; S2. Weigh 65.5% of the 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, mass ratio 1:1.2) in proportion, and the liquid-solid ratio is 0.65; S3. Complexation reaction: The coal gangue powder is mixed with a citric acid (pH 3 - 4) solution, and 0.2% of disodium EDTA is added, and stirred at 60 °C for 2 hours to ensure that the complexation rate of Al 3+ , Fe 3+ is ≥ 80%; S4. Gradient foaming: Calcium carbonate is added in two portions to control the CO2 release rate (interval 15 min), stirred at room temperature for 30 minutes, 50% is added for the first time to initiate the initial pores of CO2 (pH 4.5 - 5.0), and the second addition realizes continuous foaming (pH 5.5 - 6.0), and the target gas production of CO2 is ≥ 200 mL / g; S5, Solidification and Gelation: Add phosphogypsum in batches to avoid Ca 2+ -citrate precipitation. In the first stage, add 40% of the total amount after S3 and before S4 to promote the reaction of Ca 2+ with SiO3 2- to form calcium silicate gel (C-S-H), forming an initial skeleton structure; in the second stage, add the remaining 60% in the middle stage of S4 foaming to form a dense gel network. The gelation efficiency is increased by ≥85%, the porosity of the final product is ≥65%, and the compressive strength is ≥2.0 MPa, meeting the requirements of saline-alkali soil remediation. First stage: Stir at 150 rpm for 10 minutes until the pH is 5-6 and the temperature is 25 °C; second stage: Stir at a low speed of 50 rpm for 5 minutes, the temperature is 50 °C, and the pH rises to 7.0-7.5.

[0031] S6, Grouting and Foaming: Pour the obtained slurry into a mold and let it stand still and foam for 30 min to obtain a foam body.

[0032] S7, Gradient Pressure Curing: Pass CO2 gas (pressure 0.33 MPa) into the foam body obtained in S6, cure at 50 °C for the first 24 hours (to accelerate the formation of C-S-H gel), and cure at 35 °C for the next 30 hours (to stabilize the pore structure). The porosity is ≥65% and the compressive strength is ≥2.0 MPa; S8, Gradient Temperature Drying: Since high-silicon materials are brittle and prone to cracking during drying, take out the formed foam body obtained in S7 from the mold and place it in an oven at 50-120 °C. Dry at 50 °C for 6 hours to remove surface moisture; dry at 80 °C for 8 hours, control the heating rate ≤5 °C / hour; dry at 105 °C for 4 hours to ensure that the final water content ≤5% to obtain a dry formed foam body.

[0033] S9, Uniformly mix the dry formed foam body obtained in S8 with the crushed functional filler; S10, Pelletizing: Put the dry formed foam body obtained in S9 into a jaw crusher and crush it to ≤10 mm, then use a pair-roll pelletizer to screen 3-5 mm particles, and pass through a vibrating screen (two-stage screens with pore sizes of 3 mm and 5 mm) to recycle the fine powder (<1 mm) as a filler. The whole process temperature ≤45 °C to obtain a solid waste-based porous material.

[0034] Comparative Example 1 Preparation of Solid Waste-Based Porous Material S1, Raw Material Pretreatment: Crush coal gangue to 100 mesh (150 μm) to obtain coal gangue powder; wash, neutralize, and passivate phosphogypsum, then screen it through a 20-mesh sieve (pore size 0.85 mm) to retain 0.1-0.5 mm particles; S2. Weigh out 70% of the pretreated coal gangue powder, 29.6% of phosphogypsum, and 0.4% of the foaming agent (a composite system of citric acid and calcium carbonate with a mass ratio of 1:1.2) proportionally. The liquid-solid ratio is 0.65. S3. Complexation reaction: Mix the coal gangue powder with a citric acid (pH 3 - 4) solution, add 0.2% disodium EDTA, and stir at 60 °C for 2 hours to ensure that the complexation rate of Al 3+ , Fe 3+ is ≥ 80%. S4. Gradient foaming: Add calcium carbonate in two batches to control the CO2 release rate (with an interval of 15 minutes), stir at room temperature for 30 minutes. Add 50% for the first time to initiate the initial pores of CO2 (pH 4.5 - 5.0), and add the second time to achieve continuous foaming (pH 5.5 - 6.0). The target gas production of CO2 is ≥ 200 mL / g. S5. Curing and gelling: Add phosphogypsum in batches to avoid Ca 2+ -citric acid precipitation. Add 40% of the total amount after S3 and before S4 in the first stage to promote the reaction of Ca 2+ with SiO3 2- to form calcium silicate gel (C-S-H) and form an initial skeleton structure. Add the remaining 60% in the middle stage of S4 foaming in the second stage to form a dense gelling network. The gelling efficiency is increased by ≥ 85%. The porosity of the final product is ≥ 65%, the compressive strength is ≥ 2.0 MPa, meeting the requirements of saline-alkali soil remediation. First stage: Stir at 150 rpm for 10 minutes until the pH is 5 - 6 and the temperature is 25 °C. Second stage: Stir at a low speed of 50 rpm for 5 minutes, the temperature is 50 °C, and the pH rises to 7.0 - 7.5.

[0035] S6. Grouting and foaming: Pour the obtained slurry into a mold and let it stand and foam for 30 minutes to obtain a foamed body.

[0036] S7. Gradient pressure curing: Pass CO2 gas (pressure 0.33 MPa) into the foamed body obtained in S6. Cure at 50 °C for the first 24 hours (to accelerate the formation of C-S-H gel), and then cure at 35 °C for the next 30 hours (to stabilize the pore structure). The porosity is ≥ 65%, and the compressive strength is ≥ 2.0 MPa. S8. Gradient temperature drying: Since high-silica materials are brittle and prone to cracking during drying, take out the formed foamed body obtained in S7 from the mold and place it in an oven at 50 - 120 °C. Dry at 50 °C for 6 hours to remove surface moisture; dry at 80 °C for 8 hours, controlling the heating rate ≤ 5 °C / hour; dry at 105 °C for 4 hours to ensure that the final moisture content is ≤ 5% to obtain a dried formed foamed body.

[0037] S9. Granulation: The dried formed foam obtained in S8 is put into a jaw crusher and crushed to ≤10 mm, and then 3-5 mm particles are screened by a pair-roll granulator, and passed through a vibrating screen (with two-stage screens of 3 mm and 5 mm apertures), and the fine powder (<1 mm) is recycled as a filler. The temperature throughout the process is ≤45 °C to obtain the solid waste-based porous material.

[0038] Refer to the methods of Example 2 to Example 3 to prepare the solid waste-based soil conditioner. Comparative Example 2 Common soil improvers in the prior art The components of the existing solid waste-based porous soil improver 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, by mass.

[0039] The performance of the coal-based solid waste porous materials in Example 1, Comparative Example 1 and Comparative Example 2 was compared and analyzed, and the results are shown in Table 1 below.

[0040] Table 1. Performance analysis results of Example 1, Comparative Example 1 and Comparative Example 2 The solid waste-based porous material in Example 1 was compared and analyzed with Comparative Example 1 and Comparative Example 2 from four aspects: from the perspective of pore size distribution, the bimodal type in Example 1 breaks through the traditional unimodal / irregular distribution, realizing the synergistic effect of rapid water conduction in macropores (the permeability increases by 40% within 30 seconds) and long-term water retention in micropores (the 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 (the traditional material < 0.5), and the water molecule diffusion coefficient reaches 2.3×10 -6 m 2 / s. From the perspective of heavy metal fixation, the fixation rates of Cd / Pb break through the 99% threshold, and XPS binding energy analysis shows that stable lattice structures are formed by Cd-O bonds (406.8 eV) and Pb-P bonds (138.5 eV). From the perspective of pH buffering, the pH dynamic balance is achieved through the CaCO3 / silicate slow-release system, and the effective action period is extended by 3 times compared with commercial products.

[0041] Proof of innovation: The bimodal pore size distribution of the solid waste-based porous material in Example 1 (as shown in Figure 1 、 2 ) realizes the synergy of rapid water absorption (macropores) and long-term water retention (micropores); it is confirmed by XPS analysis (as shown in Figure 3 ) that heavy metals exist in the stable state of CdSiO3 / Pb3(PO4)2.

[0042] 1. Cd chemical state analysis The Cd 3d5 / 2 binding energy is located at 406.8 eV. This peak position corresponds to the formation of the Cd-O bond, indicating that Cd is stably fixed through oxygen coordination bonds.

[0043] Compared with the standard CdO reference value (405.0 eV), the binding energy has a positive shift of 1.8 eV, indicating a stronger electron cloud polarization effect in the lattice structure.

[0044] 2. Pb chemical state analysis The Pb4f7 / 2 peak appears at 138.5 eV, with a 0.6 eV negative shift compared to metal sulfide (137.9 eV of PbS), confirming the unique coordination environment of the Pb-P bond.

[0045] The Pb-0 characteristic peak (~137 eV) was not detected, excluding oxide interference.

[0046] Example 2 Using the solid waste-based porous material prepared in Example 1 to prepare a solid waste-based soil conditioner Mix the solid waste-based porous material prepared in Example 1 and functional auxiliaries (woody peat and urea) according to the gradient formula set according to the degree of soil salinization. After mixing, add 2-3% of the total mass of the composite bacterium agent, and perform aerobic fermentation for 7-10 days (temperature 30-40 °C, turning frequency 3 days / time) to obtain a solid waste-based soil conditioner.

[0047] Slightly saline soil: 67%-79% of solid waste-based porous material, 20%-30% of woody peat, 1.0%-3.0% of urea; moderately saline soil: 55%-72% of solid waste-based porous material, 25%-40% of woody peat, 3.0%-5% of urea; severely saline soil: 50%-66% of solid waste-based porous material, 30%-44% of woody peat, 4.0%-6.0% of urea.

[0048] Physically crush the woody peat raw material with a high-speed shear machine to a particle size not exceeding 1 mm to obtain woody peat powder.

[0049] According to the degree of soil salinization, it is recommended to add 200–500 kg of solid waste-based soil conditioner per mu, and regularly detect the soil EC value (electrical conductivity), pH and C / N ratio, and adjust the subsequent topdressing strategy.

[0050] The Trichoderma harzianum liquid and Bacillus subtilis were activated and cultured to obtain two bacterial liquid cultures. The two liquid cultures were mixed at a volume ratio of 1:1, and sterile distilled water containing 0.1% Tween 80 was added and shaken evenly to prepare a composite bacterial liquid. The composite bacterial liquid was inoculated into a solid waste-based porous material medium containing 10%-15% woody peat, with the humidity maintained at 40-60% and the temperature at 25-35°C. After aerobic culturing for 7 days, it was crushed to a particle size of <2 mm. The obtained bacterial agent was inoculated into a new medium at a ratio of 10-15% and cyclically propagated 2-3 times to prepare a composite bacterial agent with a total viable count of ≥2×10 8 CFU / g.

[0051] Trichoderma harzianum was inoculated on a PDA solid medium and cultured at 25-30°C for 7 days until the colony produced spores. Bacillus subtilis was inoculated into an LB liquid medium and cultured on a shaker at 35-37°C for 24 hours until the OD600 value reached 0.8-1.0. The viable count of the Trichoderma harzianum liquid culture was 1×10 8 spores / mL, and the viable count of the Bacillus subtilis liquid culture was 8×10 8 spores / mL.

[0052] Trichoderma harzianum secretes extracellular polysaccharides to promote the formation of soil aggregates, and the phosphorus and potassium solubilization efficiency is increased by 40%. Bacillus subtilis produces organic acids to passivate heavy metals (the passivation rate of Cd / Pb / Cr ≥ 85%), and at the same time inhibits the proliferation of pathogenic bacteria. The composite bacterial agent is significantly superior to the single bacterial agent in promoting plant growth and stress resistance, and the coal gangue conditioner requires a relatively high initial bacterial amount to overcome the stress of the saline-alkali environment.

[0053] Example 3 Using the solid waste-based soil conditioner prepared in Example 2 for saline-alkali land ecological restoration Soil pretreatment: The saline-alkali land was plowed (depth 20-30 cm), large soil masses were broken, and the air permeability was increased. A mixture of porous materials and woody peat was applied and mechanically plowed and mixed evenly. If the pH > 9.5 or the salt content > 10 g / kg, leaching to reduce salt (the EC value of the leaching water ≤ 1.5 mS / cm) was required in advance.

[0054] Mix according to the ratio of conditioner:bacterial agent:water = 100:2-3:80-100 (mass ratio). The environmental conditions were controlled as temperature 15-35°C, air humidity ≥ 60%, avoiding direct strong light irradiation; wind speed ≤ level 4 to prevent the bacterial agent from drifting.

[0055] Spraying operation: Bottom spraying: First, spray the bacterial agent-containing conditioner mixture (thickness 5-8 cm) to promote microbial colonization; Surface covering: Cover with humus soil or planting soil (thickness 3-5 cm) to protect the microbial community; Seed / vegetation layer: Sow salt-tolerant plant seeds (such as sea buckthorn, Suaeda salsa), and cover with soil with a thickness of 1-2 cm.

[0056] Spraying operation parameters: spraying rate 20 - 30 m³ / h, water content: the water content of the mixed liquid is controlled at 40% - 50%, pH adjustment: monitor in real time after spraying, and add citric acid if necessary (maintain pH 6.0 - 7.0).

[0057] Post - construction management Moisture - retaining maintenance: Immediately cover with non - woven fabric or straw after spraying (light transmittance ≤ 30%) to reduce water evaporation; spray water for replenishment regularly (twice a day in the initial stage for 15 consecutive days) to keep the soil water content ≥ 20%.

[0058] Monitoring of microbial activity: Regularly collect soil samples (depth 0 - 20 cm) to detect the number of microorganisms (total number of colonies ≥ 1×10 7 CFU / g); monitor the activities of soil enzymes (such as urease, dehydrogenase) to evaluate the recovery of microbial functions.

[0059] Dynamic regulation: If the EC value > 2 mS / cm or pH > 8.5, spray a modifier containing woody peat; in areas with severe saline - alkali stress, add a drip irrigation system to supplement the bacterial solution (concentration diluted to 1×10 6 CFU / mL).

[0060] Apply the solid - waste - based soil conditioner prepared by the present invention to the soils of different saline - alkali land types, and compare with the untreated control area (p < 0.01, t - test), observe the application effect, and the results of salt determination using the saturated extraction method (USDA method) are shown in Table 2 below.

[0061] Table 2. Comparison of soil changes after applying the solid - waste - based soil conditioner in different geological conditions Apply the solid - waste - based soil conditioner to chloride - type, sulfate - type, and soda - salinized soils, and the EC value decreases and meets the secondary standard for farmland, the crop yield increases, and the microbial diversity increases. It shows that applying the solid - waste - based soil conditioner prepared in this application to different saline - alkali types has achieved triple breakthroughs in improving the physical structure, optimizing the chemical properties, and reconstructing the biological functions of saline - alkali land.

[0062] Apply the solid - waste - based soil conditioner prepared in this application to the saline - alkali area of the Inner Mongolia project, and the continuous five - year tracking data are shown in Table 3 below: Table 3. Comparison of soil changes after applying the solid - waste - based soil conditioner in the saline - alkali area for five consecutive years As can be seen from Table 3, the soil alkalinity degree (ESP) continuously decreases: the initial ESP is 21.4% and drops to 7.1% in the 5th year. The calcium - based solid waste in the conditioner replaces Na 2+ adsorbed by soil colloids +, reducing the sodium adsorption ratio (SAR); the ESP still showed a downward trend in the 5th year, indicating that the slow-release calcium source (such as phosphogypsum) in the conditioner continuously released Ca 2+ , inhibiting the return of sodium salts. The organic matter and microbial biomass carbon increased significantly: the organic matter increased from 3.8 g / kg to 9.5 g / kg; the solid waste-based porous material had more pores to adsorb organic humic acid; at the same time, auxiliary materials such as woody peat provided exogenous organic carbon. The microbial biomass carbon increased by 349%: the porous structure improved the soil air permeability and promoted the reproduction of aerobic microorganisms; the decomposition of organic matter released carbon sources and activated functional bacteria (such as Bacillus subtilis). The corn yield increased step by step: the yield increased from 1.2 t / ha to 6.2 t / ha; the reduction of ESP alleviated sodium toxicity and promoted the absorption of nutrients by roots; the enhanced microbial activity improved the release efficiency of nutrients in the solid waste-based soil conditioner.

[0063] For coastal chloride saline-alkali soil, a solid waste-based conditioner formula of 57% solid waste-based porous material, 38% woody peat, and 5% urea was selected. The saline-alkali land was plowed (depth 20 - 30 cm) to break up large soil masses and increase air permeability. 3.5 t / ha of porous material, 2.3 t / ha of woody peat, and 0.3 t / ha of urea were mixed and mechanically plowed and mixed evenly; if pH > 9.5 or salt content > 10 g / kg, pre-washing for salt reduction was required (the EC value of the washing water ≤ 1.5 mS / cm). It was mixed according to the ratio of solid waste-based porous material conditioner:bacterial agent:water = 100:2 - 3:80 - 100 (mass ratio). Spraying operations were carried out on the saline-alkali soil to be treated. Immediately after spraying, non-woven fabric or straw was covered (light transmittance ≤ 30%) to reduce water evaporation; regular spray water replenishment was carried out (twice a day in the initial stage for 15 days) to keep the soil moisture content ≥ 20%.

[0064] The results showed that: the Cl leaching rate in 30 days - Leaching rate: 68.5% (control group: 22.3%), the soil aggregates (>0.25 mm) increased to 41.7% (initial 12.5%), and real-time PCR detection showed that the copy number of functional genes (such as nifH) increased by 4.2 times. The application of this solid waste-based soil conditioner achieved efficient desalination, structure improvement, and ecological function restoration of coastal saline-alkali soil, and its Cl - leaching rate, aggregate stability, and microbial activity data were all better than those of traditional conditioners. In the future, through large-scale field verification and optimization of process parameters, its promotion and application value in coastal saline-alkali areas can be further improved.

[0065] The above is only the preferred embodiment of the present invention and is not used to limit the present invention. For those skilled in the art, the present invention can also have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A solid waste-based porous material for repairing saline-alkali soil, characterized in that: 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.

2. The solid waste-based porous material for repairing saline-alkali soil according to claim 1, characterized in that: The gangue powder is the gangue from 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, and the foaming agent is a composite system of citric acid and calcium carbonate, with a mass ratio of 1:1.

2.

3. According to claim 2, a method for preparing a solid waste-based porous material for repairing saline-alkali soil is characterized by: The specific steps of the preparation method are as follows: S1. Raw material pretreatment: crush the coal gangue to 100 mesh to obtain coal gangue powder; wash, neutralize and passivate the phosphogypsum and pass it through a 20-mesh sieve to retain 0.1-0.5 mm particles; crush the functional filler; S2. quantitatively weighing the pretreated coal gangue powder, phosphogypsum, functional filler and foaming agent according to the proportion distribution; S3, complex reaction: Mix the 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, add the second time to achieve continuous foaming, and the CO2 target gas production is ≥200mL / g; S5. Solidification and gelling: Add phosphogypsum in batches to avoid Ca 2+ It reacts with citric acid to precipitate. 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) to form 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: passing CO2 gas through the foam obtained in S6, curing at 50°C for the first 24 hours, and curing at 35°C for the next 30 hours to obtain a molded foam; S8, gradient temperature drying: the molded foam obtained in S7 is removed from the mold, placed in a 50-120°C oven, and dried at 50°C for 6 hours to remove surface moisture; the second time is dried at 80°C for 8 hours, and the heating rate is controlled to be ≤5°C / hour; the third time is dried at 105°C for 4 hours to ensure that the final moisture content is ≤5%, thereby obtaining a dry molded foam; S9, uniformly mixing the dried molded foam obtained in S8 with the crushed functional filler; S10, granulation: the dried molded foam obtained in S9 is put into a jaw crusher and crushed to ≤10mm, and then a double-roll 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°C to obtain a solid waste-based porous material.

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

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

0. 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 pH 5-6, temperature 25 degrees; the second stage: low-speed stirring at 50 rpm for 5 minutes, temperature 50°C, pH rises to 7.0-7.

5.

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

7. The use of a solid waste-based porous material for repairing saline-alkali soil according to claim 2, characterized in that: The solid waste-based porous material is used for preparing a soil conditioner.

8. The use of a solid waste-based porous material for repairing saline-alkali soil according to claim 7, characterized in that: The soil conditioner comprises a solid waste-based porous material, a functional auxiliary material and a composite bacterial agent.

9. The use of a solid waste-based porous material for repairing saline-alkali soil according to claim 8, 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.

10. The use of a solid waste-based porous material for repairing saline-alkali soil according to claim 9, 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, 1.0%-3.0% urea; moderate saline-alkali soil: 55%-72% solid waste-based porous material, 25%-40% woody peat, 3.0%-5% urea; severe saline-alkali soil: 50%-66% solid waste-based porous material, 30%-44% woody peat, 4.0%-6.0% urea; the Trichoderma harzianum liquid and Bacillus subtilis 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 particles are broken to a particle size of <2 mm; the number of viable bacteria in the Trichoderma harzianum liquid is 1×10 8 spores / mL, and the number of viable bacteria of the Bacillus subtilis liquid was 8×10 8 Spores / mL.

Images