Liquorice planting method based on cooperative utilization of coal-based solid waste and desertification land

Abstract

The invention relates to the technical field of soil improvement and ecological restoration, and discloses a liquorice planting method based on synergistic utilization of coal-based solid waste and desertified land, which comprises the following steps: crushing alkaline coal-based solid waste and acidic coal-based solid waste, mixing according to a mass ratio of 2: 8-4: 6, adding a modified humic acid-based heavy metal passivator and water, and uniformly mixing to obtain a mixture; uniformly mixing and aging to obtain a coal-based solid waste mixture; spreading the mixture on the surface layer of the desertification land, performing rotary tillage and deep tillage to mix the mixture with the sandy soil, and adjusting the pH value to be stable at 7.5-8.5; the treated liquorice seeds are sown, main roots are harvested in autumn of the third year, deep root systems and lateral root bud points are reserved, and overground straw is smashed and returned to the field; soil nutrition indexes are monitored regularly, other commercial crops are planted when the soil nutrition indexes reach a set threshold value, and if not, regeneration planting of the liquorice is maintained. Through synergistic compounding of acid-base solid waste and chelating of the passivating agent, substrate pH self-regulation and heavy metal resistance control are achieved, and the physicochemical property of sandy soil is improved.

Description

Technical Field

[0001] This invention relates to the field of soil improvement and ecological restoration technology, specifically a licorice planting method based on the synergistic utilization of coal-based solid waste and desertified land. Background Technology

[0002] The mining and utilization of coal resources generates a large amount of coal gangue and fly ash, coal-based solid waste. Currently, the main methods for treating this type of solid waste are stockpiling and landfilling, which not only occupy land resources but also cause harmful components to migrate and pollute the surrounding soil and groundwater through leaching with rainwater. On the other hand, there are large areas of desertified land in Northwest my country, where the wind-blown sand particles are large and loosely structured, with poor water and fertilizer retention capacity, and low content of organic matter and nitrogen and phosphorus nutrients, hindering vegetation growth.

[0003] Existing technologies attempt to improve soil using coal-based solid waste, but several problems arise in practical applications: First, different types of coal-based solid waste exhibit significant differences in acidity and alkalinity. Some coal gangue becomes acidic after oxidation, while fly ash is typically alkaline. Direct application without regulation leads to unstable soil pH, inhibiting plant root growth. Second, coal-based solid waste contains heavy metals such as lead, cadmium, and mercury, which are converted into bioavailable forms in the soil environment and absorbed by plants, resulting in excessive heavy metal levels in planted crops. Third, simple physical mixing cannot construct stable aggregate structures in sandy soil, failing to improve the poor water and fertilizer retention of desertified land, leading to low plant survival rates. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a licorice cultivation method based on the synergistic utilization of coal-based solid waste and desertified land. This method solves the problems in existing technologies where single treatment methods are difficult to simultaneously address the resource utilization of coal-based solid waste and the efficient improvement of desertified land, and where the use of solid waste to improve soil faces the risk of heavy metal accumulation and unstable soil physicochemical properties.

[0005] To achieve the above objectives, the present invention provides the following technical solution: The first aspect of this invention provides a licorice cultivation method based on the synergistic utilization of coal-based solid waste and desertified land. This method utilizes the synergistic complementarity of acid-base solid waste and chemical passivation technology to construct a soil matrix suitable for plant growth, and combines specific planting and harvesting strategies to achieve ecological restoration and economic benefit recycling. The method includes the following steps: First, coal-based solid waste is modified. Alkaline and acidic coal-based solid wastes are crushed and physically mixed at a mass ratio of 2:8 to 4:6.

[0006] Subsequently, 1.5% to 3.0% of the total mass of the two materials were added as a modified humic acid-based heavy metal passivating agent and water. After stirring evenly, the mixture was aged to obtain a coal-based solid waste mixture.

[0007] This step utilizes the difference in chemical properties between acidic solid waste coal gangue and alkaline solid waste fly ash to achieve preliminary acid-base self-neutralization; Meanwhile, the active groups in the modified humic acid-based heavy metal passivating agent are used to complex and fix the heavy metal ions released from solid waste, thereby reducing their bioavailability.

[0008] The next step is to improve the soil by mixing coal-based solid waste with sand. The coal-based solid waste mixture is evenly spread on the surface of the desertified land, with a thickness controlled at 5-10 cm. Deep tillage is then performed using rotary tillage to ensure thorough mixing of the solid waste mixture with the topsoil. The fine particles of the coal-based solid waste fill the pores between the coarse particles of the sand, increasing the soil's specific surface area and water-holding capacity, and initially establishing a soil aggregate structure that retains water and nutrients.

[0009] Subsequently, a second precise pH adjustment was performed. The pH value was measured after the mixed soil layer was allowed to stand for 24 hours, and the second adjustment was carried out based on the measurement results. When the pH value is greater than 8.5, add acid-regulating materials and neutralize by rotary tillage; When the pH value is less than 7.5, add alkaline conditioning material and rotary tillage to neutralize it.

[0010] This step eliminates pH rebounds or fluctuations caused by delayed hydrolysis of solid waste mineral components or environmental factors, ensuring that the soil environment remains stable within the suitable range of 7.5 to 8.5 for licorice growth.

[0011] Next, licorice is planted and harvested. Pretreated licorice seeds are sown in the conditioned mixed soil layer. Harvesting takes place in the autumn of the third year. The harvesting process involves cutting and collecting the taproot, preserving the deep root system and lateral root buds in situ, and returning the above-ground straw to the field. Preserving the deep root system utilizes the nitrogen-fixing function of licorice root nodules, a characteristic of leguminous plants, to continuously improve the nitrogen level in the deep soil and provide physical anchoring for the soil, preventing wind erosion caused by exposed soil after harvest. Returning the straw to the field further replenishes soil organic matter.

[0012] Finally, dynamic monitoring of soil nutrient conditions and crop rotation decisions are conducted. After straw is crushed and returned to the field, the organic matter, available nitrogen, available phosphorus, and pH values ​​of the mixed soil layer are monitored regularly. When all monitored indicators reach the set thresholds, it indicates that the soil physicochemical properties have been improved to the required standard. At this time, residual roots are removed and other cash crops with higher requirements for water and fertilizer are planted. If the indicators do not meet the standards, licorice regeneration is maintained by retaining the roots and buds, and soil maturation and improvement continue.

[0013] In a preferred embodiment, the alkaline coal-based solid waste is selected from fly ash emitted from coal-fired power plants, with a pH value of 9.0–11.5 and a particle size passing through a 200-mesh sieve; the acidic coal-based solid waste is selected from coal gangue stored for more than 3 years, with the main mineral components including kaolinite and pyrite, and a pH value of 3.5–5.5. The particle size distribution of the crushed mixture is controlled as follows: particles larger than 2 mm account for 15%–20%, particles with a diameter of 0.05–2 mm account for 40%–50%, and particles smaller than 0.05 mm account for 30%–45%. This specific particle size distribution utilizes larger coal gangue particles to construct the soil framework, and fine fly ash particles and clay minerals to fill the pores, forming a framework-filling structure with suitable porosity and mechanical strength, thus improving the loose structure of aeolian sandy soil.

[0014] In a preferred embodiment, the modified humic acid-based heavy metal passivating agent is prepared from the following raw materials in parts by weight: 100 parts of weathered coal-derived humic acid (free humic acid content greater than 60%), 25-35 parts of acrylamide, 1.5-2.5 parts of N,N'-methylenebisacrylamide, 0.8-1.2 parts of potassium persulfate, and 10-15 parts of 3-mercaptopropyltrimethoxysilane. The passivating agent is prepared by first preparing a humate solution with a pH of 10.0-10.5 from humic acid, then adding acrylamide monomer, a crosslinking agent, and an initiator, reacting at 75-85°C to form a hydrogel precursor, and finally adding 3-mercaptopropyltrimethoxysilane dropwise at 50-55°C for a grafting reaction. This technical solution introduces a polyacrylamide network structure and thiol functional groups onto the humic acid molecular backbone. Polyacrylamide segments adsorb soil and solid waste particles through hydrogen bonds and van der Waals forces, promoting aggregate formation; the thiol groups work synergistically with the carboxyl and phenolic hydroxyl groups in humic acid to chelate lead and cadmium heavy metal ions through coordination bonds, which not only prevents heavy metals from migrating to plants, but also improves the chemical stability of the passivating agent in complex soil environments.

[0015] In a preferred embodiment, during the pretreatment of coal-based solid waste, the water-to-solid ratio is 0.1:1 to 0.2:1, and the aging time is 48 to 72 hours. Appropriate moisture content and aging time ensure sufficient ion exchange and pozzolanic reaction between the acidic and alkaline solid wastes, promoting the formation of aluminosilicate gels and providing a cementing foundation for subsequent bonding with sand and soil.

[0016] In a preferred embodiment, the specific parameters for the secondary adjustment are as follows: when pH > 8.5, desulfurized gypsum is selected as the acidity adjustment material, with an addition amount of 1.0–2.0 kg / mu, utilizing the calcium ions in the gypsum to replace sodium ions on the soil colloids and neutralize excess alkalinity; when pH < 7.5, biochar is selected as the alkalinity adjustment material, with an addition amount of 1.5–2.5 kg / mu, utilizing the porosity and surface alkaline groups of biochar to buffer acidity and simultaneously adsorb free heavy metals.

[0017] In a preferred embodiment, the rotary tillage depth is controlled at 25–35 cm, and the rotary tillage blade rotation speed is 220–260 r / min. These parameters ensure that the improved layer thickness covers the main root distribution area of ​​licorice, while avoiding damage to the underlying native soil structure.

[0018] In a preferred embodiment, the licorice seed treatment process involves: treating the seeds with a friction machine until the seed coat abrasion rate reaches 90%–95%, and then soaking them in warm water at 40–50℃ for 6–8 hours. This combined physical and hydrothermal treatment breaks down the hard seed coat barrier of licorice seeds, increases the water penetration rate, and significantly improves the germination rate. The sowing rate is controlled at 1.5–2.0 kg / mu, with a soil covering thickness of 1.5–2.0 cm to ensure a reasonable population density and seedling vigor.

[0019] In a preferred embodiment, the digging depth during harvesting is 30–40 cm, collecting taproots with a diameter greater than 0.5 cm; the above-ground straw is pulverized and returned to the field by rotary tillage to a depth of 10–15 cm. This harvesting strategy balances the yield of medicinal herbs with the needs of ecological restoration, preserving the organic pores formed by the root system during decomposition, which is beneficial for soil aeration and water permeability.

[0020] In a preferred embodiment, the crop rotation threshold is set as follows: soil organic matter ≥1.5%, available nitrogen ≥60mg / kg, available phosphorus ≥15mg / kg, and pH maintained between 7.5 and 8.5; the subsequent crop rotation is wolfberry. The threshold setting is based on the critical indicators for transforming desertified land into mature farmland. Wolfberry, as a crop with high economic value and certain requirements for water and fertilizer conditions, not only continues the ecological restoration effect but also enhances the economic added value of land use.

[0021] This invention provides a licorice cultivation method based on the synergistic utilization of coal-based solid waste and desertified land. It has the following beneficial effects: 1. This invention utilizes the complementary properties of the alkalinity of fly ash and the acidity of coal gangue. By controlling the mixing ratio of the two and the particle size distribution after crushing, the acid-base self-neutralization and physical structure reorganization of coal-based solid waste are achieved. The specific ratio of the mixture adjusts the pH value of the matrix, reducing the dependence on exogenous chemical regulators. At the same time, the mixing of solid waste particles of different sizes with desert sand changes the single loose structure of the sand, increases the soil porosity and specific surface area, thereby improving the water and fertilizer retention capacity of the improved soil, and realizing the synergistic effect of resource utilization of coal-based solid waste and desertification land improvement.

[0022] 2. The modified humic acid-based heavy metal passivating agent used in this invention has a three-dimensional network structure and multiple active functional groups, which can simultaneously achieve heavy metal passivation and soil moisture retention. The grafted thiol groups and the original carboxyl and phenolic hydroxyl groups of humic acid form stable complexes with heavy metal ions in solid waste through coordination, reducing the bioavailability of heavy metals and blocking their migration to licorice plants. At the same time, the cross-linked network constructed by polyacrylamide segments has water absorption and swelling properties, which can effectively store water and release it slowly in arid desert environments, alleviating water stress during plant growth.

[0023] 3. This invention accelerates the soil maturation process through a cyclical operation of licorice planting, harvesting specific parts, and returning straw to the field. It increases soil nitrogen sources by utilizing the nitrogen-fixing effect of licorice rhizobia, fixes sandy soil by retaining deep roots and lateral root buds, and increases deep organic matter through root decomposition. Combined with the return of crushed straw to the field, it enhances the fertility of the topsoil. This biological approach increases the content of soil organic matter, available nitrogen, and available phosphorus, providing a soil fertility foundation for the rotational succession from tolerant crops to high-value crops. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the method flow of the present invention. Detailed Implementation

[0025] Preparation Examples 1-3: Preparation Example 1: This preparation example provides a modified humic acid-based heavy metal passivating agent, the raw material components of which include: 100 parts of weathered coal-derived humic acid, 30 parts of acrylamide, 2.0 parts of N,N'-methylenebisacrylamide, 1.0 part of potassium persulfate, and 12.5 parts of 3-mercaptopropyltrimethoxysilane; Includes the following steps: (1) Dissolve 100 parts of humic acid in deionized water, add 1 mol / L sodium hydroxide solution to adjust the pH to 10.2, and stir at 400 r / min for 40 minutes in a 65℃ water bath to obtain sodium humate solution. (2) Add 30 parts acrylamide, 2.0 parts N,N'-methylenebisacrylamide and 1.0 parts potassium persulfate to the above solution in sequence, purge with nitrogen for protection, heat to 80°C, and react for 3.5 hours to form humic acid-polyacrylamide hydrogel precursor; (3) Lower the temperature to 52°C, add 12.5 parts of 3-mercaptopropyltrimethoxysilane dropwise, and continue the reaction for 2.5 hours; (4) After the product is precipitated with anhydrous ethanol and washed three times with deionized water, it is dried in a vacuum oven at 60°C for 24 hours and then pulverized through a 100-mesh sieve to obtain the modified humic acid-based heavy metal passivating agent.

[0026] Preparation Example 2: This preparation example provides a modified humic acid-based heavy metal passivating agent, the raw material components of which include: 100 parts of weathered coal-derived humic acid, 25 parts of acrylamide, 1.5 parts of N,N'-methylenebisacrylamide, 0.8 parts of potassium persulfate, and 10 parts of 3-mercaptopropyltrimethoxysilane. Includes the following steps: (1) Dissolve 100 parts of humic acid in deionized water, add 1 mol / L sodium hydroxide solution to adjust the pH to 10.0, and stir at 300 r / min for 30 minutes in a 60℃ water bath to obtain sodium humate solution. (2) Add 25 parts acrylamide, 1.5 parts N,N'-methylenebisacrylamide and 0.8 parts potassium persulfate to the above solution in sequence, purge with nitrogen for protection, heat to 75°C, react for 3 hours to form humic acid-polyacrylamide hydrogel precursor; (3) Lower the temperature to 50°C, add 10 parts of 3-mercaptopropyltrimethoxysilane, and continue the reaction for 2 hours; (4) After the product is precipitated with anhydrous ethanol and washed three times with deionized water, it is dried in a vacuum oven at 60°C for 24 hours and then pulverized through a 100-mesh sieve to obtain the modified humic acid-based heavy metal passivating agent.

[0027] Preparation Example 3: This preparation example provides a modified humic acid-based heavy metal passivating agent, the raw material components of which include: 100 parts of weathered coal-derived humic acid, 35 parts of acrylamide, 2.5 parts of N,N'-methylenebisacrylamide, 1.2 parts of potassium persulfate, and 15 parts of 3-mercaptopropyltrimethoxysilane. Includes the following steps: (1) Dissolve 100 parts of humic acid in deionized water, add 1 mol / L sodium hydroxide solution to adjust the pH to 10.5, and stir at 500 r / min for 45 minutes in a 70℃ water bath to obtain sodium humate solution. (2) Add 35 parts acrylamide, 2.5 parts N,N'-methylenebisacrylamide and 1.2 parts potassium persulfate to the above solution in sequence, purge with nitrogen for protection, heat to 85°C, react for 4 hours to form humic acid-polyacrylamide hydrogel precursor; (3) Lower the temperature to 55°C, add 15 parts of 3-mercaptopropyltrimethoxysilane, and continue the reaction for 3 hours; (4) After the product is precipitated with anhydrous ethanol and washed three times with deionized water, it is dried in a vacuum oven at 60°C for 24 hours and then pulverized through a 100-mesh sieve to obtain the modified humic acid-based heavy metal passivating agent.

[0028] Examples 1-3: Example 1: This embodiment provides a licorice cultivation method based on the synergistic utilization of coal-based solid waste and desertified land, including the following steps: (1) Pretreatment of coal-based solid waste: Alkaline coal-based solid waste (fly ash) and acidic coal-based solid waste (coal gangue) were crushed separately. The proportion of particles larger than 2 mm in the crushed mixture was controlled to be 18%, particles between 0.05 and 2 mm to be 45%, and particles smaller than 0.05 mm to be 37%. Take the crushed solid waste, add the modified humic acid-based heavy metal passivating agent prepared in Preparation Example 1 at 2.2% of the total mass of the solid waste, spray with water with a water-to-solid ratio of 0.15:1, and stir in a forced mixer for 18 minutes. The optimal mass blending ratio of alkaline coal-based solid waste to acidic coal-based solid waste was determined to be 3:7 through small-scale experiments. The two were mixed in a twin-shaft mixer according to this ratio, and an appropriate amount of water was added to adjust the moisture content to 18%. The mixture was aged in a sealed stockpile for 48 hours to obtain a coal-based solid waste mixture with a pH value of 8.1.

[0029] (2) Improvement by mixing coal-based solid waste with sand: The coal-based solid waste mixture obtained in step (1) is evenly spread on the surface of the desertified land to be improved, with a thickness of 8cm. Deep tillage is carried out using a rotary tiller with a tillage depth of 30cm, a rotary blade shaft speed of 240r / min, and a travel speed of 1.0m / s, so that solid waste and sand are mixed evenly. After standing for 24 hours, the pH value of the mixed soil layer at 0-20cm was measured to be 8.0, which is within the range of 7.5-8.5, and no secondary adjustment is required.

[0030] (3) Planting and harvesting of licorice: Ural licorice seeds were selected and treated with a centrifugal seed abrasion machine until the seed coat abrasion rate was 92%. They were then soaked in 45℃ warm water for 7 hours, drained, and mixed with fine sand at a volume ratio of 1:3. In early April, mechanical row sowing is used, with a sowing rate of 1.8 kg / mu, row spacing of 35 cm, furrow depth of 2.5 cm, and soil covering thickness of 1.8 cm, followed by compaction. Harvest in October of the third year of planting, dig to a depth of 35cm, cut and collect the main root with a diameter greater than 0.5cm, and retain the deep root system and lateral root buds; Crush the straw on the ground, spread it, and then rotary till it into the soil to a depth of 12cm.

[0031] (4) Dynamic monitoring of soil nutrient conditions and optimization of crop rotation: Soil samples from 0-40cm depth are collected quarterly to monitor nutrient levels. When organic matter ≥1.5%, available nitrogen ≥60mg / kg, available phosphorus ≥15mg / kg, and pH is maintained between 7.5 and 8.5, root clearing and harvesting are carried out and the soil is replanted with wolfberry. If the indicators are not met, the regeneration and cultivation of licorice will continue.

[0032] Example 2: This embodiment provides a licorice cultivation method based on the synergistic utilization of coal-based solid waste and desertified land, including the following steps: (1) Pretreatment of coal-based solid waste: Alkaline coal-based solid waste and acidic coal-based solid waste were crushed separately. The proportion of particles larger than 2 mm in the crushed mixture was controlled to be 15%, particles between 0.05 and 2 mm to be 40%, and particles smaller than 0.05 mm to be 45%. Take the crushed solid waste, add the modified humic acid-based heavy metal passivating agent prepared in Preparation Example 2 at 1.5% of the total mass of the solid waste, spray with water with a water-to-solid ratio of 0.1:1, and stir in a forced mixer for 15 minutes. The optimal mass mixing ratio of alkaline coal-based solid waste to acidic coal-based solid waste was determined to be 2:8 through small-scale experiments. The two were mixed according to this ratio, and an appropriate amount of water was added to adjust the moisture content to 15%. The mixture was aged for 48 hours to obtain a coal-based solid waste mixture.

[0033] (2) Improvement by mixing coal-based solid waste with sand: The coal-based solid waste mixture obtained in step (1) is evenly spread on the surface of the desertified land to be improved, with a thickness of 5cm. Deep tillage was carried out using a rotary tiller, with a tillage depth of 25cm, a rotary tiller shaft speed of 220r / min, and a travel speed of 0.8m / s; After standing for 24 hours, the pH value of the mixed soil layer was measured to be 8.8 (greater than 8.5). Desulfurized gypsum powder was added at a rate of 1.5 kg / mu for secondary rotary tillage and neutralization. After equilibration for 24 hours, the pH value was measured again to be 8.3.

[0034] (3) Planting and harvesting of licorice: Seed treatment was the same as in Example 1, with a sowing rate of 1.5 kg / mu, row spacing of 30 cm, furrow depth of 2 cm, and soil covering thickness of 1.5 cm. Harvest in the autumn of the third year after planting, dig to a depth of 30cm, and leave roots in the same way as in Example 1; The straw is pulverized and rotary tilled to a depth of 10cm.

[0035] (4) Dynamic monitoring of soil nutrient conditions and optimization of crop rotation: The monitoring and decision-making logic is the same as in Example 1.

[0036] Example 3: This embodiment provides a licorice cultivation method based on the synergistic utilization of coal-based solid waste and desertified land, including the following steps: (1) Pretreatment of coal-based solid waste: Alkaline coal-based solid waste and acidic coal-based solid waste were crushed separately. The proportion of particles larger than 2 mm in the crushed mixture was controlled to be 20%, particles between 0.05 and 2 mm to be 50%, and particles smaller than 0.05 mm to be 30%. Take the crushed solid waste, add the modified humic acid-based heavy metal passivating agent prepared in Preparation Example 3 at 3.0% of the total mass of the solid waste, spray with water with a water-to-solid ratio of 0.2:1, and stir in a forced mixer for 20 minutes. The optimal mass blending ratio of alkaline coal-based solid waste to acidic coal-based solid waste was determined to be 4:6 through small-scale experiments. The two were mixed according to this ratio, and an appropriate amount of water was added to adjust the moisture content to 20%. The mixture was aged for 72 hours to obtain a coal-based solid waste mixture.

[0037] (2) Improvement by mixing coal-based solid waste with sand: The coal-based solid waste mixture obtained in step (1) is evenly spread on the surface of the desertified land to be improved, with a thickness of 10cm. Deep tillage was carried out using a rotary tiller, with a tillage depth of 35cm, a rotary blade shaft speed of 260r / min, and a travel speed of 1.2m / s; After standing for 24 hours, the pH value of the mixed soil layer was measured to be 7.2 (less than 7.5). Biochar powder was added at a rate of 2.0 kg / mu for secondary rotary tillage to neutralize the soil. After equilibration for 24 hours, the pH value was measured again to be 7.8.

[0038] (3) Planting and harvesting of licorice: Seed treatment was the same as in Example 1, with a sowing rate of 2.0 kg / mu, row spacing of 40 cm, furrow depth of 3 cm, and soil covering thickness of 2.0 cm; Harvest in the autumn of the third year after planting, digging to a depth of 40cm, and leaving roots in the same way as in Example 1; The straw is pulverized and rotary tilled to a depth of 15cm.

[0039] (4) Dynamic monitoring of soil nutrient conditions and optimization of crop rotation: The monitoring and decision-making logic is the same as in Example 1.

[0040] Comparative Examples 1-6: Comparative Example 1: Compared with Example 1, the difference is that: no coal-based solid waste was mixed and improved, that is, steps (1) and (2) were not carried out; licorice was planted directly on the original desertified land in step (3), and the water and fertilizer management during the planting period was the same as in Example 1.

[0041] Comparative Example 2: Compared with Example 1, the difference is that only alkaline coal-based solid waste (fly ash) is used in step (1), and acidic coal-based solid waste (coal gangue) is not added; in order to adjust the pH value to 8.1, industrial dilute sulfuric acid is used for acid-base neutralization treatment, and the rest of the steps are the same.

[0042] Comparative Example 3: Compared with Example 1, the difference is that the modified humic acid-based heavy metal passivating agent prepared in Example 1 was not added in step (1), and only physical crushing and blending and aging of acid and alkali solid waste were carried out. The other steps are the same.

[0043] Comparative Example 4: Compared with Example 1, the difference is that the heavy metal passivating agent used in step (1) is replaced with an equal mass of commercially available ordinary polyacrylamide (PAM, molecular weight 12 million), and the other steps are the same.

[0044] Comparative Example 5: Compared with Example 2, the difference is that in step (2), when the pH value of the mixed soil layer is measured to be 8.8 (greater than 8.5), desulfurized gypsum is not added for secondary neutralization and adjustment, but the state is directly maintained for subsequent planting. The other steps are the same.

[0045] Comparative Example 6: Compared with Example 1, the difference is that the harvesting method in step (3) is changed to the traditional digging method, that is, the digging depth is 50cm, and all the licorice roots (including the main root, lateral roots and fibrous roots) are dug out, without deliberately preserving the deep roots and root buds. The rest of the steps are the same.

[0046] Test Examples 1-2: Test Example 1: Evaluation of the physicochemical stability and environmental safety of the modified matrix.

[0047] Experimental description: This test aims to verify the acid-base buffering capacity and heavy metal retention stability of the coal-based solid waste sand-soil mixture matrix treated by the method of this invention under simulated natural environmental conditions. Modified mixed soil samples prepared in Examples 1-3, as well as corresponding soil samples from Comparative Example 2 (without acidic solid waste synergy / only chemical acid adjustment), Comparative Example 3 (without passivating agent), and Comparative Example 4 (with ordinary PAM passivating agent) were selected as test subjects.

[0048] Experimental steps: The improved mixed soil samples prepared in Examples 1 to 3, as well as the soil samples corresponding to Comparative Examples 2, 3, and 4, were selected as test subjects. 500g of freshly prepared mixed soil samples from each group were placed in an environment of 25±2℃ and 60% relative humidity. Deionized water was sprayed onto the soil surface every 3 days to maintain the soil moisture content between 60% and 70% of field capacity. Soil samples were collected on days 1, 7, 15, 30, and 60, and suspensions were prepared at a soil-to-water ratio of 1:2.5. The pH value was determined using the potentiometric method. Dry samples from each group after 60 days of curing were also taken, and leaching toxicity tests were conducted according to the HJ / T299-2007 standard. A sulfuric acid-nitric acid mixture with a pH of 3.20±0.05 was used as the extraction solvent, with a liquid-to-solid ratio of 10:1, and the mixture was shaken for 18 hours. After filtration through a 0.45μm filter and digestion, the concentrations of lead, cadmium, and chromium were determined using inductively coupled plasma mass spectrometry.

[0049] Experimental data: Table 1. Dynamic changes in pH value of each mixed substrate during simulated culture.

[0050] Table 2. Heavy metal leaching concentrations (mg / L) in the matrix of each group after 60 days of curing.

[0051] in conclusion: The pH values ​​of the mixed matrices in Examples 1 to 3 fluctuated by less than 0.15 during the 60-day monitoring period, consistently remaining in the slightly alkaline range. In Comparative Example 2, which only used acid to adjust the fly ash, the pH value rebounded to above 9.0 in the later stages. This is because the examples utilized a mixture of acidic coal gangue and alkaline fly ash. The clay minerals in the coal gangue reacted with the active calcium oxide in the fly ash to form an aluminosilicate gel system, providing ion exchange sites and acid-base buffering capacity, thus inhibiting the delayed release of residual alkali from the fly ash. Comparative Example 2 lacked a mineral buffering system and experienced a pH rebound under alternating moisture conditions.

[0052] Heavy metal leaching tests showed that the heavy metal leaching concentrations in Examples 1 to 3 met the relevant standard requirements and were lower than those in the comparative example. The lead and cadmium leaching amounts in Example 1 were significantly lower than those in Comparative Example 3 without the added passivating agent, confirming the chemical retention effect of the custom-modified humic acid-based passivating agent. The thiol groups in this passivating agent form coordination bonds with heavy metal ions such as lead and cadmium, and the humic acid framework further fixes the metal ions through ion exchange. Comparative Example 4 used ordinary polyacrylamide, which easily desorbed heavy metals under acidic leaching conditions, and its stability was not as good as the modified passivating agent containing thiol groups and humic acid structures.

[0053] Test Example 2: Comprehensive evaluation of field planting efficiency and soil ecological restoration.

[0054] Experimental description: This test aims to verify the long-term effects of the planting method of this invention on licorice growth indicators, medicinal quality and safety, and soil physicochemical properties improvement in practical applications. The experimental site was selected at a semi-arid desertification experimental base in Northwest China, and the experimental period was 3 years (one complete planting cycle).

[0055] Experimental steps: Experimental plots were established in a semi-arid desertification experimental base, each plot covering 667 m², with isolation strips. Soil pretreatment, sowing, and field management were carried out according to the methods of Examples 1 to 3 and Comparative Examples 1 to 6, with a cycle of 3 years. In the autumn of the third year, after the licorice harvest, soil samples were collected from the 0-40 cm topsoil layer using a five-point sampling method to determine soil bulk density, content of water-stable aggregates larger than 0.25 mm, and organic matter content. The number of surviving plants was counted and the survival rate was calculated in randomly selected quadrats, and the yield per mu was calculated. The glycyrrhizic acid content in dried rhizomes was determined using high-performance liquid chromatography. The lead and cadmium content in the licorice roots and corresponding soil were measured, and the bioaccumulation coefficient was calculated. For Examples 1 and 6, the number of regrowth plants per unit area was counted in the spring of the following year.

[0056] Experimental data: Table 3. Effects of soil physicochemical property improvement in each experimental area in the autumn of the third year.

[0057] Table 4. Statistics on Licorice Yield, Quality, and Safety Indicators

[0058] Table 5. Assessment of Crop Rotation Potential and Regeneration Capacity

[0059] in conclusion: The soil bulk density in Examples 1 to 3 was reduced to 1.21-1.28 g / cm³. 3 The content of water-stable large aggregates increased to over 35%. Coal gangue particles formed a skeleton in the sandy soil, fly ash microspheres filled the gaps, and the binding effect of polymer segments in the passivating agent improved the soil pore structure and wind erosion resistance. Comparative Example 2 relied solely on chemical regulation, lacking skeleton materials and organic binders, resulting in poor aggregate structure formation.

[0060] In the example group, the yield of licorice per mu (approximately 0.067 hectares) remained stable at over 800 kg, with a survival rate exceeding 89%. In contrast, in Comparative Example 5, the initial high pH environment inhibited seedling growth due to the lack of secondary pH adjustment, resulting in a lower survival rate. The glycyrrhizic acid content in all example groups exceeded 3.0%, indicating that the trace elements released from coal-based solid waste are beneficial for the synthesis of secondary metabolites.

[0061] In Example 1, the bioaccumulation coefficients of lead and cadmium remained at a low level, while those in Comparative Example 3, which did not contain a passivating agent, were higher. The modified passivating agent reduced the bioavailability of heavy metals through complexation, blocking their transfer into plants. In Example 1, soil nutrient indicators met the requirements for crop rotation by the end of the third year, and the number of plants that greened up the following year was relatively high. Comparative Example 6 involved whole-root excavation, which removed rhizosphere nitrogen fixation products and damaged root channels, resulting in low soil organic matter accumulation and poor regeneration capacity, confirming the necessity of a root-retaining harvesting strategy for maintaining soil fertility and ecological restoration.

Claims

1. A method for licorice cultivation based on the synergistic utilization of coal-based solid waste and desertified land, characterized in that, Includes the following steps: Alkaline coal-based solid waste and acidic coal-based solid waste are crushed and mixed in a mass ratio of 2:8 to 4:

6. Modified humic acid-based heavy metal passivating agent and water are added at a total mass of 1.5% to 3.0% of the two, and the mixture is mixed and aged to obtain a coal-based solid waste mixture. The coal-based solid waste mixture was spread on the surface of the desertified land and then rotary tilled and deeply plowed to mix it evenly with the sand. After standing, the pH value of the mixed soil layer is measured and adjusted a second time by adding acidic or alkaline conditioning materials and rotary tilling to neutralize it until the pH value stabilizes between 7.5 and 8.

5. The treated licorice seeds were sown in the conditioned mixed soil layer, and the licorice was harvested in the autumn of the third year. The harvesting includes: cutting and collecting the taproot, retaining the deep root system and lateral root buds in situ, and crushing the above-ground straw and returning it to the field; After straw is returned to the field, the mixed soil index is monitored regularly. When all the indexes reach the set threshold, the residual roots are removed and other cash crops are planted. Otherwise, the deep roots and lateral root buds are used to maintain the regeneration of licorice.

2. The licorice cultivation method based on the synergistic utilization of coal-based solid waste and desertified land according to claim 1, characterized in that, The alkaline coal-based solid waste is fly ash emitted from coal-fired power plants, with a pH value of 9.0 to 11.5 and a particle size passing through a 200-mesh sieve. The acidic coal-based solid waste is coal gangue that has been stored for more than 3 years. Its main mineral components include kaolinite and pyrite, and its pH value is 3.5 to 5.

5. The particle size distribution of the mixture of alkaline coal-based solid waste and acidic coal-based solid waste after crushing meets the following conditions: particles with a diameter greater than 2 mm account for 15% to 20%, particles with a diameter of 0.05 to 2 mm account for 40% to 50%, and particles with a diameter less than 0.05 mm account for 30% to 45%.

3. The licorice cultivation method based on the synergistic utilization of coal-based solid waste and desertified land according to claim 1, characterized in that, The modified humic acid-based heavy metal passivating agent is made from raw materials comprising the following parts by weight: Weathered coal-derived humic acid (free humic acid content greater than 60%): 100 parts; Acrylamide: 25-35 parts; N,N'-methylenebisacrylamide: 1.5-2.5 parts; Potassium persulfate: 0.8-1.2 parts; 3-mercaptopropyltrimethoxysilane: 10-15 parts.

4. A licorice cultivation method based on the synergistic utilization of coal-based solid waste and desertified land according to claim 3, characterized in that, The preparation method of the modified humic acid-based heavy metal passivating agent includes the following steps: Humic acid is dissolved in water, and the pH is adjusted to 10.0-10.5 by adding alkaline solution. The solution is stirred at 60-70°C to obtain a humate solution. Acrylamide, N,N'-methylenebisacrylamide and potassium persulfate were added to the humate solution, and the mixture was heated to 75-85°C under nitrogen protection and reacted for 3-4 hours to form a hydrogel precursor. Cool the temperature to 50-55℃, add 3-mercaptopropyltrimethoxysilane dropwise, and continue the reaction for 2-3 hours. The modified humic acid-based heavy metal passivating agent is obtained by precipitation, washing, drying and pulverizing the product.

5. A licorice cultivation method based on the synergistic utilization of coal-based solid waste and desertified land according to claim 1, characterized in that, The water-to-solid ratio of the added water to the total mass of the alkaline coal-based solid waste and the acidic coal-based solid waste is 0.1:1 to 0.2:1; the aging time is 48 to 72 hours.

6. A licorice cultivation method based on the synergistic utilization of coal-based solid waste and desertified land according to claim 1, characterized in that, The specific method of the secondary adjustment is as follows: When the pH value is greater than 8.5, desulfurized gypsum, which is used as the acidity adjusting material, is added at a rate of 1.0 to 2.0 kg / mu. When the pH value is less than 7.5, biochar, which is used as the alkaline adjustment material, is added at a rate of 1.5 to 2.5 kg / mu.

7. A licorice cultivation method based on the synergistic utilization of coal-based solid waste and desertified land according to claim 1, characterized in that, The thickness of the spread layer is 5-10cm; the rotary tillage depth is 25-35cm, and the rotary tillage blade shaft speed is 220-260r / min.

8. A method for licorice cultivation based on the synergistic utilization of coal-based solid waste and desertified land according to claim 1, characterized in that, The method for obtaining the treated licorice seeds is as follows: Licorice seeds were treated with a friction machine until the seed coat abrasion rate was 90%–95%, and then soaked in warm water at 40–50°C for 6–8 hours. The sowing rate is 1.5–2.0 kg / mu, and the soil covering thickness is 1.5–2.0 cm.

9. A method for licorice cultivation based on the synergistic utilization of coal-based solid waste and desertified land according to claim 1, characterized in that, The digging depth during harvesting is 30-40cm, collecting the main roots with a diameter greater than 0.5cm; the rotary tillage depth for returning the above-ground straw to the field is 10-15cm.

10. A method for licorice cultivation based on the synergistic utilization of coal-based solid waste and desertified land according to claim 1, characterized in that, The monitoring indicators and set thresholds are: soil organic matter ≥1.5%, available nitrogen ≥60mg / kg, available phosphorus ≥15mg / kg, and pH maintained between 7.5 and 8.5; The other economic crop mentioned is wolfberry.

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