A high-fertility coal gangue ecological soil, its preparation method and its application

Abstract

This invention discloses a high-fertility coal gangue ecological soil, its preparation method, and its application, belonging to the field of solid waste resource utilization and soil remediation technology. The preparation method includes the following steps: Step S1. Crushing coal gangue and agricultural and forestry straw; Step S2. Mixing coal gangue and agricultural and forestry straw to obtain a mixture, and adding nano-iron powder to obtain mixed particles; Step S3. Pyrolyzing the mixed particles to obtain an ecological soil matrix; Step S4. Mixing the ecological soil matrix with loess, exogenous humic acid, and microbial agents evenly to obtain coal gangue ecological soil. This invention utilizes the high surface activity of nano-iron powder to reduce the oxidation activation energy of pyrite at low temperatures and catalyze the depolymerization and condensation of biomass lignin to generate humic acid-like substances. The iron oxides generated by pyrolysis and the newly generated humic acid work synergistically to solidify heavy metals into a stable residue state, resulting in coal gangue ecological soil with good air permeability, water retention, and high organic fertility.

Description

Technical Field

[0001] This invention belongs to the field of solid waste resource utilization and soil remediation technology, specifically relating to a high-fertility coal gangue ecological soil, its preparation method and its application. Background Technology

[0002] As a major coal producer and consumer, my country generates a large amount of coal gangue solid waste during coal mining, with a cumulative stockpile exceeding 6 billion tons, and annual new emissions consistently reaching hundreds of millions of tons. Among these, high-sulfur coal gangue, due to its high sulfur content and high mineral activity, faces three prominent problems: a significant risk of spontaneous combustion, easy leaching and migration of heavy metals, and continuous release of acidic pollution, making its remediation far more difficult than that of ordinary coal gangue. The sulfur in high-sulfur coal gangue mainly exists in the form of pyrite, which reacts with air and moisture under natural conditions, continuously releasing heat. This heat accumulation easily triggers spontaneous combustion of gangue piles, releasing large amounts of toxic and harmful gases such as sulfur dioxide and hydrogen sulfide, severely polluting the regional atmospheric environment. The oxidation process is accompanied by the generation of acidic mine drainage, causing the violent leaching of heavy metals such as lead, cadmium, arsenic, and chromium, which are then leached into the soil and groundwater by rainwater, resulting in excessive levels of heavy metals in water and soil, threatening ecological security and human health. Although the mineral composition of coal gangue is very similar to that of natural soil, giving it an inherent advantage for large-scale soil utilization, its resource utilization still faces a core dilemma.

[0003] In existing technologies, the harmless treatment of coal gangue mostly adopts high-temperature calcination (>800℃), which can desulfurize but consumes extremely high energy and easily leads to the destruction of mineral structure and complete carbonization of organic matter, failing to retain soil fertility. On the other hand, agricultural and forestry straw can not be directly used as a soil substitute due to the lack of mineral framework when composted or pyrolyzed alone. Moreover, there is currently no technology that can simultaneously achieve deep desulfurization, heavy metal stabilization, and organic matter humification transformation of coal gangue under low-temperature conditions. At the same time, my country has a huge annual output of biomass resources such as agricultural and forestry straw, which are widely available, but the overall resource utilization rate is low. A large amount of straw is mainly burned in the field, randomly piled up, and simply landfilled, which not only wastes organic carbon resources but also causes environmental problems such as smog and eutrophication of water bodies. There is a lack of efficient, clean, and high-value large-scale disposal pathways.

[0004] Coal gangue is rich in inorganic minerals but lacks organic matter and fertility, while agricultural and forestry straw is abundant in carbon sources and easily decomposes. The two are highly complementary in composition and characteristics, possessing natural potential for synergistic resource utilization. However, mature technologies for the efficient coupling and utilization of both are currently lacking. The ecological hazards of high-sulfur coal gangue, the inherent defects of traditional technologies, and the practical need for the resource-based disposal of agricultural and forestry straw together constitute the urgent background for this technology development. There is an urgent need to develop a low-temperature, efficient, and clean synergistic disposal technology that can achieve deep desulfurization of coal gangue, in-situ stabilization of heavy metals, and complete elimination of spontaneous combustion risk while significantly reducing energy consumption, and simultaneously convert agricultural and forestry straw into high-fertility ecological restoration materials, providing a feasible path for the coordinated development of solid waste reduction, pollution control, and ecological agriculture in mining areas. Summary of the Invention

[0005] The technical problem to be solved by this invention is to provide a method for preparing high-fertility coal gangue ecological soil that is low-temperature, high-efficiency, and can simultaneously achieve desulfurization, weight consolidation, and decomposition enhancement, addressing the shortcomings of existing coal gangue disposal methods such as high energy consumption, low fertility, easy activation of heavy metals, and single resource utilization pathways for agricultural and forestry straw.

[0006] The core concept of this invention lies in utilizing the nano-size effect and extremely high surface activity of nano-iron powder as a bifunctional catalyst introduced into the pyrolysis system. On the one hand, in a low-temperature oxygen-containing atmosphere, nano-iron powder significantly reduces the activation energy of pyrite oxidation through interfacial electron transfer and Fenton-like reactions, achieving deep desulfurization and recovering sulfur resources. On the other hand, nano-iron powder catalyzes the depolymerization of lignin in agricultural and forestry straw into small-molecule phenolic monomers, and generates humic acid-like substances with structures highly similar to natural soil humic acid in situ through Maillard reactions. Simultaneously, the iron oxides generated in the reaction form a synergistic passivation system with the newly generated humic acid, transforming heavy metals into a stable residual state through adsorption, complexation, and lattice encapsulation. Finally, by combining loess with functional microbial agents, ecological soil with good air permeability, water retention, and high organic fertility is obtained.

[0007] To achieve the objectives of this invention, the technical solution is as follows: A method for preparing high-fertility coal gangue ecological soil, comprising the following steps: Step S1. Provide coal gangue and agricultural and forestry straw, and mix the coal gangue, agricultural and forestry straw and nano iron powder to obtain a mixture; Step S2. The mixture is subjected to pyrolysis under an oxygen-containing atmosphere to obtain an ecological soil matrix; Step S3. Mix the ecological soil matrix with exogenous humic acid and microbial inoculant to obtain the high-fertility coal gangue ecological soil.

[0008] Preferably, in the method for preparing the high-fertility coal gangue ecological soil, step S1 further includes a pretreatment step: crushing and sieving the coal gangue to a particle size of 1-5 mm; crushing the agricultural and forestry straw to 80-200 mesh; and the nano-iron powder having a particle size of 1-100 nm.

[0009] Preferably, in the method for preparing the high-fertility coal gangue ecological soil, in step S1, the mass ratio of coal gangue to agricultural and forestry straw is 1:0.2 to 1:0.8; and the amount of nano-iron powder added accounts for 0.1% to 2% of the total mass of the mixture.

[0010] Preferably, in the method for preparing the high-fertility coal gangue ecological soil, in step S2, the oxygen-containing atmosphere is composed of oxygen and inert gas, wherein the volume fraction of oxygen is 3%~10%; the temperature of the pyrolysis reaction is 200℃~350℃, and the reaction time is 30~120min.

[0011] Preferably, in the method for preparing the high-fertility coal gangue ecological soil, step S2 further includes a tail gas treatment step, specifically: collecting the sulfur-containing gas generated by pyrolysis, absorbing it through water or dilute acid spray to prepare sulfuric acid, and discharging the remaining tail gas after washing with alkaline solution.

[0012] Preferably, in the method for preparing the high-fertility coal gangue ecological soil, step S3 further includes adding loess to the ecological soil matrix; the mass ratio of the ecological soil matrix, loess, exogenous humic acid, and microbial agent is 40~70:20~50:1~5:0.1~2.

[0013] Preferably, in the method for preparing the high-fertility coal gangue ecological soil, the exogenous humic acid is selected from one of ammonium humate, potassium humate, and sodium humate; and the microbial agent is selected from at least one of rhizobium, Bacillus megaterium, and Bacillus subtilis.

[0014] Preferably, in the method for preparing the high-fertility coal gangue ecological soil, the solid product after pyrolysis in step S2 is cooled and then sieved to a particle size ≤ 5 mm to obtain the ecological soil matrix.

[0015] A high-fertility coal gangue ecological soil, comprising the following components in parts by weight: 40-70 parts ecological soil matrix, 20-50 parts loess, 1-5 parts exogenous humic acid, and 0.1-2 parts microbial inoculant.

[0016] Preferably, the high-fertility coal gangue ecological soil is used as a crop cultivation substrate, a mining area ecological restoration substrate, or a slope greening substrate.

[0017] Compared with existing technologies, the advantages of this invention are: (1) Ultra-low temperature high efficiency catalysis, significantly reducing energy consumption and carbon emissions: Relying on the nano-size effect and extremely high surface activity of nano iron powder, the pyrolysis reaction temperature of coal gangue is significantly reduced to 200℃~350℃. Compared with the traditional high temperature calcination (>800℃) process, the overall energy consumption is reduced by more than 60%, and carbon emissions are significantly reduced, which meets the requirements of green and low-carbon development.

[0018] (2) Achieving deep desulfurization and sulfur resource recycling: Traditional physical washing can only remove 30% to 50% of pyrite sulfur from coal gangue. Chemical desulfurization is costly and easily generates secondary wastewater. High-temperature desulfurization has problems of high energy consumption and serious sulfur escape. In this invention, nano iron powder induces strong oxidizing free radicals through interfacial electron transfer and Fenton-like reaction, which can efficiently catalyze the complete oxidation and decomposition of pyrite at low temperature. The desulfurization rate can be stably up to 90% to 95%, which solves the pollution hazards of residual sulfur from the root. At the same time, the high concentration of sulfur oxide flue gas generated by pyrolysis can be absorbed by multi-stage spraying to prepare 10% to 20% concentration of industrial grade dilute sulfuric acid, realizing the recycling of sulfur resources, turning waste into treasure, and significantly improving the overall economic efficiency and environmental friendliness of the process.

[0019] (3) In-situ efficient stabilization of heavy metals and blocking environmental migration pathways: After the reaction, the nano iron powder is converted into nano / micro iron oxides, which form a synergistic system with the humic acid generated simultaneously. Through the triple action of adsorption complexation, reduction precipitation and lattice encapsulation, the heavy metals such as Pb, Cd and As in coal gangue are converted from easily exchangeable state to stable residue state, which greatly reduces their environmental migration and bioavailability.

[0020] (4) Simultaneous enrichment of humic acid to endow the product with high organic fertility: Coal gangue itself has extremely low organic matter content, dense structure, and poor water and fertilizer retention capacity. Traditional treatment products can only be used as building materials or roadbed fillers and cannot be used in agriculture. Under mild oxidation conditions, this invention uses the catalytic effect of nano iron powder to directionally depolymerize lignin in agricultural and forestry straw into small molecule phenolic monomers. Then, through Maillard reaction and polyphenol polymerization reaction, humic acid-like substances with a structure highly similar to natural black soil humic acid are generated in situ. The humic acid content in the product can reach 15%~25%, of which the proportion of fulvic acid is significantly increased. The generated humic acid can effectively improve soil aggregate structure, improve cation exchange capacity, and enhance water and fertilizer retention performance, directly making up for the fertility defects of coal gangue and giving the product the core functional attributes of soil-like substances.

[0021] (5) Eliminate the risk of spontaneous combustion of coal gangue from the root: Through low-temperature catalytic oxidation, the pyrite and other sulfides in coal gangue that have spontaneous combustion activity are completely transformed. The pyrolysis products are stable and the long-standing spontaneous combustion risk of gangue mountains and the problem of drainage pollution from acid mines are completely solved. Attached Figure Description

[0022] Figure 1 This is a process flow diagram for preparing high-fertility coal gangue ecological soil according to the present invention.

[0023] Figure 2 A process flow diagram for the collection, crushing, and resource utilization of coal gangue solid waste to prepare coal gangue.

[0024] Figure 3 This is a physical image of the ecological soil matrix prepared in Example 1 of the present invention.

[0025] Figure 4 This is an XPS image of the ecological soil matrix obtained after pyrolysis in Example 1.

[0026] Figure 5 This is a SEM image of the ecological soil matrix obtained after pyrolysis in Example 1.

[0027] Figure 6 This is a comparison chart showing the growth effect of wheat planted in coal gangue ecological soil and ordinary soil prepared in Example 1 for 28 days. Detailed Implementation

[0028] The present invention will be further described below with reference to specific drawings and embodiments; in the present invention, unless otherwise specified, all raw materials used in the preparation are commercially available products well known to those skilled in the art.

[0029] Example 1 A method for preparing high-fertility coal gangue ecological soil includes the following steps: Step S1. Provide coal gangue and agricultural and forestry straw. The coal gangue is high-sulfur coal gangue from a coal mine in Shanxi (total sulfur content 4.5%, Pb 135mg / kg, Cd 2.1mg / kg, As 28mg / kg, Cr 42mg / kg). After crushing, it is sieved to 1~5mm particles without any chemical modification or physical activation treatment. The agricultural and forestry straw is naturally dried and then crushed to 100 mesh powder. Step S2. Provide nano-iron powder with an average particle size of 50nm. Add the crushed coal gangue and agricultural and forestry straw from step S1 into a mixer at a mass ratio of 1:0.6 to obtain a mixture. The mixer speed is 300r / min and the mixing time is 15min. Add 1% of the total mass of nano-iron powder to the mixture and continue mixing for 15min. Then add water to adjust the moisture content to 15%, reduce the speed to 200r / min, and mix for 10min to obtain mixed particles of 5~10mm. Step S3. The mixed particles obtained in step S2 are placed in a rotary pyrolysis reactor and heated in an oxygen-containing atmosphere (oxygen volume fraction of about 4.2%) where air and nitrogen are mixed in a volume ratio of 1:4. The pyrolysis reaction is carried out at a temperature of 280°C for 75 minutes. The pyrolysis solid product is naturally cooled to room temperature and sieved to ≤5mm to obtain ecological soil matrix. The sulfur oxide gas generated by pyrolysis is collected through pipelines and passed into a two-stage spray absorption tower. It is sprayed with water to absorb and prepare 12% industrial grade dilute sulfuric acid. The tail gas is washed with 10% sodium hydroxide solution and discharged after meeting the standards. Step S4. Provide exogenous humic acid, which is potassium humate; provide microbial inoculant, which is Bacillus subtilis with an effective viable count ≥1 billion / g; add the ecological soil matrix obtained in step S3, loess, exogenous humic acid, and microbial inoculant into a mixer at a mass ratio of 60:32:5:1 and mix at a speed of 60 r / min for 25 min to obtain high-fertility coal gangue ecological soil.

[0030] A high-fertility coal gangue ecological soil comprises the following components in parts by weight: 60 parts ecological soil matrix, 32 parts loess, 5 parts exogenous humic acid, and 1 part complex microbial agent.

[0031] Example 2 This embodiment systematically verifies the core catalytic role of nano-iron powder in this system and the adjustability of process parameters by setting up a blank control group, a control group of ordinary micron-sized iron powder, and two experimental groups of nano-iron powder with different parameters. Except for the type of catalyst, particle size and amount added, the source of raw materials, pretreatment method and process parameters are completely consistent with those in Example 1.

[0032] Catalyst grouping: Blank group: No catalyst added; Control group: Ordinary micron-sized iron powder (particle size 10~20μm, specific surface area 0.8m² / g); Experimental group 1: Nano iron powder A (average particle size 50nm, specific surface area 32m² / g, addition amount 1.0%); Experimental group 2: Nano iron powder B (average particle size 80nm, specific surface area 24m² / g, addition amount 0.8%); Microbial agent: Bacillus subtilis.

[0033] Example 3 A method for preparing high-fertility coal gangue ecological soil includes the following steps: Step S1. Provide coal gangue and agricultural and forestry straw. The coal gangue is high-sulfur coal gangue from a coal mine in Shanxi (total sulfur content 4.5%, Pb 135mg / kg, Cd 2.1mg / kg, As 28mg / kg, Cr 42mg / kg). After crushing, it is sieved to 1~5mm particles without any chemical modification or physical activation treatment. The agricultural and forestry straw is naturally dried and then crushed to 100 mesh powder. Step S2. Provide nano-iron powder with an average particle size of 50nm. Add the crushed coal gangue and agricultural and forestry straw from step S1 into a mixer at a mass ratio of 1:0.6 to obtain a mixture, wherein the coal gangue is 1000g and the agricultural and forestry straw is 600g. The mixer speed is 300r / min and the mixing time is 15min. Add nano-iron powder A and nano-iron powder B to the mixture respectively. The amount of nano-iron powder A added accounts for 1% of the total mass of the mixture, and the amount of nano-iron powder A added is 160g. The amount of nano-iron powder B added accounts for 1% of the total mass of the mixture, and the amount of nano-iron powder B added is 160g. Continue to stir for 15min. Then add water to adjust the moisture content to 15%, reduce the speed to 200r / min, and mix for 10min to obtain two groups of mixed particles of 5~10mm. Step S3. Place the two sets of mixed particles obtained in step S2 into a rotary pyrolysis reactor. In an oxygen-containing atmosphere (oxygen volume fraction of about 4.2%), in which air and nitrogen are mixed at a volume ratio of 1:4, the temperature is raised to 250℃, 280℃, 300℃, and 350℃ respectively, and the pyrolysis reaction is carried out for 75 minutes. The pyrolysis solid product is naturally cooled to room temperature and sieved to ≤5mm to obtain ecological soil matrix. The sulfur oxide gas generated by pyrolysis is collected through pipelines and passed into a two-stage spray absorption tower. Water is sprayed to absorb and prepare 12% industrial grade dilute sulfuric acid. The tail gas is washed with 10% sodium hydroxide solution and discharged after meeting the standards. Step S4. Provide a microbial inoculant, which is Bacillus subtilis with an effective viable count ≥1 billion / g; add the ecological soil matrix obtained in step S3, loess, exogenous humic acid, and microbial inoculant into a mixer at a mass ratio of 60:32:5:1 and mix at a speed of 60 r / min for 25 min to obtain high-fertility coal gangue ecological soil.

[0034] A high-fertility coal gangue ecological soil comprises the following components in parts by weight: 60 parts ecological soil matrix, 32 parts loess, 5 parts exogenous humic acid, and 1 part microbial agent.

[0035] This embodiment examines the effect of different pyrolysis temperatures on product performance. Except that the pyrolysis temperatures are set to 250℃, 300℃, and 350℃ respectively, the catalysts added are nano iron powder A and nano iron powder B respectively. The other raw materials and process parameters are completely consistent with those in Example 1.

[0036] Comparative Example 1 (Blank Control) The same coal gangue and agricultural and forestry straw as in Example 1 were mixed at a mass ratio of 1:0.6 without adding any nano-iron powder or micron-iron powder, and pyrolyzed at 280°C and with an oxygen content of 4.2%.

[0037] Comparative Example 2 (Physical Mixed Control) Using the same raw materials and proportions as in Example 1, coal gangue and agricultural and forestry straw were first pyrolyzed at 280°C. After cooling to room temperature, nano iron powder (accounting for 1% of the total mass of raw materials) was mechanically mixed into the pyrolysis product, followed by subsequent compounding steps.

[0038] Specifically: Step S1. Provide coal gangue and agricultural and forestry straw. The coal gangue is high-sulfur coal gangue from a coal mine in Shanxi (total sulfur content 4.5%, Pb 135mg / kg, Cd 2.1mg / kg, As 28mg / kg, Cr 42mg / kg). After crushing, it is sieved to 1~5mm particles without any chemical modification or physical activation treatment. The agricultural and forestry straw is naturally dried and then crushed to 100 mesh powder. Step S2. The crushed coal gangue from step S1 and agricultural and forestry straw are added to a mixer at a mass ratio of 1:0.6 to obtain a mixture. The mixer speed is 300 r / min and the mixing time is 15 min. Step S3. The mixture obtained in step S2 is placed in a rotary pyrolysis reactor. The mixture is heated in an oxygen-containing atmosphere (oxygen volume fraction of about 4.2%) with a volume ratio of air to nitrogen of 1:4 and a pyrolysis reaction is carried out at a temperature of 280℃ for 75 min. The pyrolysis solid product is allowed to cool naturally to room temperature. 1% of the total mass of nano-iron powder is added to the pyrolysis solid product and stirred for another 15 min. Then, water is added to adjust the moisture content to 15%, the stirring speed is reduced to 200 r / min, and the mixture is stirred for 10 min to obtain the ecological soil matrix. The sulfur oxide gas generated by pyrolysis is collected through a pipeline and passed into a two-stage spray absorption tower. Water is used to spray and absorb the gas to prepare 12% industrial-grade dilute sulfuric acid. The tail gas is washed with 10% sodium hydroxide solution and then discharged in compliance with emission standards. Step S4. Provide exogenous humic acid, which is potassium humate; provide microbial inoculant, which is Bacillus subtilis with an effective viable count ≥1 billion / g; add the ecological soil matrix obtained in step S3, loess, exogenous humic acid, and microbial inoculant into a mixer at a mass ratio of 60:32:5:1 and mix at a speed of 60 r / min for 25 min to obtain coal gangue ecological soil.

[0039] Comparative Example 3 (High Temperature Control) Using the same raw materials and proportions as in Example 1, pyrolysis was carried out at 650°C (the conventional high-temperature calcination temperature) under an oxygen-free nitrogen atmosphere.

[0040] Specifically: Step S1. Provide coal gangue and agricultural and forestry straw. The coal gangue is high-sulfur coal gangue from a coal mine in Shanxi (total sulfur content 4.5%, Pb 135mg / kg, Cd 2.1mg / kg, As 28mg / kg, Cr 42mg / kg). After crushing, it is sieved to 1~5mm particles without any chemical modification or physical activation treatment. The agricultural and forestry straw is naturally dried and then crushed to 100 mesh powder. Step S2. Provide nano-iron powder with an average particle size of 50nm. Add the crushed coal gangue and agricultural and forestry straw from step S1 into a mixer at a mass ratio of 1:0.6 to obtain a mixture. The mixer speed is 300r / min and the mixing time is 15min. Add 1% of the total mass of nano-iron powder to the mixture and continue mixing for 15min. Then add water to adjust the moisture content to 15%, reduce the speed to 200r / min, and mix for 10min to obtain mixed particles of 5~10mm. Step S3. The mixed particles obtained in step S2 are placed in a rotary pyrolysis reactor, heated in a nitrogen atmosphere, and subjected to pyrolysis reaction at a temperature of 650°C for 75 min. The pyrolysis solid product is naturally cooled to room temperature and sieved to ≤5 mm to obtain ecological soil matrix. The sulfur oxide gas generated by pyrolysis is collected through pipelines and fed into a two-stage spray absorption tower. Water is used to spray and absorb the gas to prepare 12% industrial grade dilute sulfuric acid. The tail gas is washed with 10% sodium hydroxide solution and discharged in compliance with standards. Step S4. Provide exogenous humic acid, which is potassium humate; provide microbial inoculant, which is Bacillus subtilis with an effective viable count ≥1 billion / g; add the ecological soil matrix obtained in step S3, loess, exogenous humic acid, and microbial inoculant into a mixer at a mass ratio of 60:32:5:1 and mix at a speed of 60 r / min for 25 min to obtain coal gangue ecological soil.

[0041] A high-fertility coal gangue ecological soil comprises the following components in parts by weight: 60 parts ecological soil matrix, 32 parts loess, 5 parts exogenous humic acid, and 1 part complex microbial agent.

[0042] Test results: 1. High-sulfur coal gangue from a coal mine in Shanxi Province was sampled and its composition was analyzed multiple times. XRD phase analysis was performed in accordance with GB / T 19227-2008. The results of sulfur occurrence speciation analysis of high-sulfur coal gangue are shown in Table 1, and the main mineral components of high-sulfur coal gangue (XRD qualitative analysis) are shown in Table 2.

[0043] Table 1

[0044] Table 2

[0045] As shown in Tables 1 and 2, the total sulfur content of the high-sulfur coal gangue used in this invention reaches 4.50%, of which pyrite sulfur accounts for 86.00%, which is the core pollutant causing spontaneous combustion of gangue piles, acid mine drainage, and heavy metal leaching. The main minerals of the raw materials are quartz and kaolinite, which are highly matched with the mineral composition of natural soil and have the inherent conditions for soil utilization. However, it has inherent defects such as heavy sulfur pollution, high heavy metal activity, and lack of organic matter. Therefore, it is necessary to achieve harmless and functional transformation through the technical solution of this invention.

[0046] 2. The comprehensive performance test results of coal gangue ecological soil in Example 1 are shown in Table 3.

[0047] Table 3

[0048] As shown in Table 3, under the preferred process conditions of this invention, the comprehensive performance of coal gangue ecological soil reaches its optimal level. The total sulfur content of the product was reduced to 0.28%, with a desulfurization rate of 93.80%. Active sulfides such as pyrite were completely converted, eliminating the risk of spontaneous combustion of coal gangue from the source. The total humic acid content of the product reached 21.60%, with fulvic acid accounting for 26.50%, which can effectively compensate for the fertility deficiency of coal gangue. The leaching concentrations of Pb, Cd, As, and Cr after treatment were far below the limits of GB5085.3-2007 standards. Heavy metals were stably solidified into residues with extremely low environmental mobility. The germination rate of pakchoi seeds was 94.20%, and the yield increased by 31.00%. The heavy metal content of the edible parts of the plants met the food safety standards of GB2762-2022, realizing the high-value utilization of solid waste in agriculture.

[0049] 3. A comparison table of key performance indicators of the coal gangue ecological soil prepared in the comparative example and Example 1 is shown in Table 4.

[0050] Table 4

[0051] Table 4 shows the performance comparison results between Comparative Examples 1-3 and Example 1. It can be seen that the simultaneous addition of nano-iron powder to the system before pyrolysis for low-temperature catalytic modification can significantly improve the desulfurization efficiency of coal gangue and the humic acid content of the product compared with no catalyst, mixing nano-iron powder after pyrolysis, and traditional high-temperature calcination process. This effectively solidifies heavy metals and reduces the risk of heavy metal leaching. Without a catalyst or with the physical mixing of iron powder in the later stage, it is difficult to achieve efficient oxidative desulfurization of pyrite and directional humification conversion of straw. The product has high sulfur residue, low organic matter, and excessive heavy metal leaching, which inhibits crop growth after application. Although traditional high-temperature calcination can achieve desulfurization, the high temperature causes a large amount of straw organic matter to decompose and almost all humic acid to be lost, resulting in poor soil fertility and weak crop yield increase. This invention utilizes the in-situ catalytic effect of nano-iron powder to simultaneously complete deep desulfurization of coal gangue, stabilization and passivation of heavy metals, and humification of agricultural and forestry straw under low temperature conditions of 200-350℃. The resulting ecological soil has excellent fertility and meets the safety standards for heavy metals. When applied to cultivation, it can significantly promote crop yield, highlighting the innovation and practicality of the process of this invention.

[0052] 4. The performance comparison results of different catalysts in Example 2 are shown in Table 5.

[0053] Table 5

[0054] Table 5 shows that nano-iron powder plays an irreplaceable core catalytic role in this system, with significantly better effects than the blank group and the ordinary micron-sized iron powder control group. The catalytic effects of no catalysis / ordinary micron-sized iron powder are relatively poor: the desulfurization rate of the blank group is only 32.00%, the humic acid content is 8.70%, the heavy metal leaching concentration exceeds the standard, and it even inhibits crop growth; the desulfurization rate of the micron-sized iron powder control group is only 58.00%, which still cannot achieve harmless treatment; the performance after catalysis by nano-iron powder is more outstanding. The desulfurization rate of both nano-iron powder experimental groups reaches more than 92%, the humic acid content increases to 19.70%~21.60%, the heavy metal leaching concentration decreases by 1~2 orders of magnitude, and the crop yield increases by 27.40%~31.00%.

[0055] Nano-iron powder, with its high specific surface area and surface activity, significantly reduces the oxidation activation energy of pyrite and simultaneously catalyzes the humification of biomass. It is the core of achieving low-temperature simultaneous desulfurization, weight consolidation, and fertilization, fully demonstrating the technical ingenuity of this invention.

[0056] 5. The results of the catalytic performance verification of nano-iron powder at different pyrolysis temperatures in Example 3 are shown in Tables 6 and 7. Table 6 is the catalytic performance table of nano-iron powder A in Experimental Group 1, and Table 7 is the catalytic performance table of nano-iron powder B in Experimental Group 2.

[0057] Table 6

[0058] Table 7

[0059] As shown in Tables 6 and 7, the nano-iron powder catalytic system of this invention has wide temperature range and high efficiency adaptability, and there is an optimal process temperature. In the low temperature range of 200℃ to 350℃, both types of nano-iron powder can achieve a desulfurization rate of over 88%, and the heavy metal stabilization effect meets the standard, significantly reducing energy consumption compared with traditional high-temperature calcination (>800℃). The optimal pyrolysis temperature is 280℃. At this temperature, the desulfurization rate, humic acid content, and crop yield increase reach their peak, and the biomass undergoes mild humification without excessive carbonization. When the temperature exceeds 300℃, humic acid undergoes thermal decomposition, and the fertility of the product decreases. Nano-iron powders of different particle sizes and addition amounts can maintain stable catalytic effects and can be flexibly adjusted according to production costs and raw material conditions, making it suitable for industrial-scale production.

[0060] Figure 1 The process flow diagram for preparing high-fertility coal gangue ecological soil according to this invention is as follows: agricultural and forestry straw is dried and crushed to 80-200 mesh → raw materials are mixed according to the formula and nano iron powder is added, water is added and granulation is carried out → low-temperature oxygen-containing atmosphere pyrolysis is performed; the pyrolysis tail gas is divided into two paths, sulfur-containing flue gas is sprayed and recovered to prepare industrial sulfuric acid, and the remaining waste gas is alkali washed to meet the emission standards → the pyrolysis solid products are cooled and screened to obtain ecological soil matrix → the matrix is ​​compounded with loess, exogenous humic acid and microbial agents to finally produce high-fertility coal gangue ecological soil.

[0061] Figure 2 This diagram illustrates the process flow for collecting, crushing, and recycling coal gangue solid waste into coal gangue. The entire chain of disposal, from raw coal mine solid waste to finished eco-friendly soil, is fully represented: coal mining generates two types of coal gangue solid waste: tunneling gangue and washing gangue → coal gangue is crushed and screened to 1~5mm.

[0062] The advantages of the invention are evidenced by its technological logic: it simultaneously consumes two major types of solid waste, high-sulfur coal gangue and waste agricultural and forestry straw, resulting in a high rate of solid waste resource utilization and solving the problems of land occupation from gangue stockpiling and pollution from straw burning; it recovers sulfur resources to produce sulfuric acid as a byproduct, turning waste into treasure and offsetting the cost of desulfurization process; the entire process is carried out at a low temperature of 200~350℃, abandoning the traditional high-temperature calcination above 800℃, which significantly reduces energy consumption and meets the requirements of low-carbon production.

[0063] Figure 3This is a physical image of the ecological soil matrix prepared in Example 1 of the present invention. The actual product is a loose, brownish-red granular material with a particle size controlled within 5 mm. The soil is loose and porous, without hard lumps, and its appearance is significantly different from the original grayish-black, dense, and hard high-sulfur coal gangue. This visually demonstrates the modification effect of the present invention: the color change confirms the in-situ generation of humic acid. The raw material coal gangue has no organic matter and is grayish-black. The dark brown color of the product comes from the humic acid-like substance generated by the depolymerization and polymerization of lignin in straw under the catalysis of nano-iron powder. The measured total humic acid content of the matrix can reach 21.6%. The high humic acid content is the reason why the product has high... The core reason for fertility is the improved soil physicochemical properties due to the loose porous structure: low-temperature pyrolysis and carbonization of straw creates pores, and the reaction of nano-iron generates iron oxides that open up the gaps between minerals, forming a rich porous structure. This significantly improves the substrate's permeability, water and fertilizer retention capacity, and solves the defects of original coal gangue such as compaction, poor water and air permeability, and inability to be directly planted. The absence of hard sulfide lumps proves that desulfurization is thorough: the original gangue contains hard pyrite crystal particles, and the product has no hard sulfur mineral agglomerates. Combined with the test results showing a desulfurization rate of 93.8%, the pyrite is basically completely decomposed, eliminating the material basis for spontaneous combustion of gangue from a physical perspective.

[0064] Figure 4 The XPS image of the ecological soil matrix prepared in Example 1 of this invention shows that sulfur is converted into a stable sulfate form. The sulfate form has stable chemical properties and significantly reduced water solubility, effectively inhibiting acid production from gangue leaching and improving the industry pain point of water and soil pollution caused by acidic leachate from high-sulfur gangue.

[0065] Figure 5 The image shows the SEM image of the ecological soil matrix prepared in Example 1 of this invention, which shows the composite porous structure formed by iron oxide and humic acid.

[0066] Figure 6 The image shows a comparison of the growth of wheat grown in coal gangue ecological soil prepared in Example 1 and wheat grown in ordinary soil after 28 days (cultivation conditions: 14h light / 10h darkness, temperature 25±2℃, relative humidity 60%, and consistent water and fertilizer management). On the left, wheat grown in ordinary soil is stunted, with yellowing leaves and weak root development; on the right, wheat grown in the coal gangue ecological soil of this invention is taller, with dark green leaves and dense roots, visually verifying the agricultural fertilizer advantages of the product.

[0067] Finally, it should be noted that the above specific embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for preparing high-fertility coal gangue ecological soil, characterized in that, Includes the following steps: Step S1. Provide coal gangue and agricultural and forestry straw, and mix the coal gangue, agricultural and forestry straw and nano iron powder to obtain a mixture; Step S2. The mixture is subjected to pyrolysis under an oxygen-containing atmosphere to obtain an ecological soil matrix; Step S3. Mix the ecological soil matrix with exogenous humic acid and microbial inoculant to obtain the high-fertility coal gangue ecological soil.

2. The method for preparing high-fertility coal gangue ecological soil according to claim 1, characterized in that, Step S1 also includes a pretreatment step: crushing and sieving the coal gangue to a particle size of 1-5 mm; crushing the agricultural and forestry straw to 80-200 mesh; and the nano-iron powder having a particle size of 1-100 nm.

3. The method for preparing high-fertility coal gangue ecological soil according to claim 1, characterized in that, In step S1, the mass ratio of coal gangue to agricultural and forestry straw is 1:0.2 to 1:0.8; the amount of nano iron powder added accounts for 0.1% to 2% of the total mass of the mixture.

4. The method for preparing high-fertility coal gangue ecological soil according to claim 1, characterized in that, In step S2, the oxygen-containing atmosphere is composed of oxygen and inert gas, wherein the volume fraction of oxygen is 3% to 10%; the temperature of the pyrolysis reaction is 200℃ to 350℃, and the reaction time is 30 to 120 min.

5. The method for preparing high-fertility coal gangue ecological soil according to claim 1, characterized in that, Step S2 also includes a tail gas treatment step, specifically: collecting the sulfur-containing gas generated by pyrolysis, absorbing it through water or dilute acid spray to prepare sulfuric acid, and discharging the remaining tail gas after washing with alkaline solution.

6. The method for preparing high-fertility coal gangue ecological soil according to claim 1, characterized in that, Step S3 also includes adding loess to the ecological soil matrix; the mass ratio of the ecological soil matrix, loess, exogenous humic acid, and microbial agent is 40~70:20~50:1~5:0.1~2.

7. The method for preparing high-fertility coal gangue ecological soil according to claim 1, characterized in that, The exogenous humic acid is selected from one of ammonium humate, potassium humate, and sodium humate; the microbial agent is selected from at least one of rhizobium, Bacillus megaterium, and Bacillus subtilis.

8. The method for preparing high-fertility coal gangue ecological soil according to claim 1, characterized in that, The solid product after pyrolysis in step S2 is cooled and then sieved to a particle size ≤ 5 mm to obtain the ecological soil matrix.

9. A high-fertility coal gangue ecological soil, characterized in that, Prepared by the method according to any one of claims 1 to 8, comprising the following components in parts by weight: 40-70 parts of ecological soil matrix, 20-50 parts of loess, 1-5 parts of exogenous humic acid, and 0.1-2 parts of microbial inoculant.

10. The application of the high-fertility coal gangue ecological soil according to claim 9, characterized in that, The high-fertility coal gangue ecological soil is used as a crop cultivation substrate, a mining area ecological restoration substrate, or a slope greening substrate.

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