Mine solid waste-based composite saline-alkali soil modifier as well as preparation method and application thereof

Abstract

The invention relates to a mine solid waste-based composite saline-alkali soil modifier as well as a preparation method and application thereof, and belongs to the technical field of soil remediation and solid waste recycling. The modifier is prepared from volcanic rock solid waste, rice husk and mussel shell as raw materials through oxalic acid activation, microbial fermentation carbonization and humic acid chelation, and comprises 50-70 parts of activated stone powder-containing porous particles, 20-30 parts of rice husk-based charcoal, 10-20 parts of humic acid chelated magnesium-calcium powder and 3-5 parts of a composite binder. The preparation method comprises the following steps: ultrasonically activating the stone powder oxalic acid, and puffing and granulating with the binder; inoculating the rice hulls with salt-tolerant bacillus and actinomycetes for aerobic fermentation and carbonization; and the shell is activated by oxalic acid and then is loaded with a humic acid calcium magnesium compound. The modifier is applied according to 50-200kg / mu, so that the nutritional ingredients and the air permeability can be improved. According to the method, solid waste recycling, solid waste consumption and landfill cost and CO2 emission reduction are achieved, and the method is suitable for ecological restoration of the coastal saline-alkali soil and has both environmental protection and economic benefits.

Description

Technical Field

[0001] The present invention relates to the technical field of soil remediation and solid waste resource utilization, and specifically to a composite saline-alkali land improver using solid wastes such as mine stone powder and mud cake as main raw materials and a preparation method thereof. The composite saline-alkali land improver is suitable for pH adjustment, sodium ion adsorption and soil structure improvement in saline-alkali land. Background Art

[0002] Saline-alkali land, due to high salt and sodium content and low organic matter content, severely restricts agricultural production. Traditional soil amendments, such as gypsum and desulfurized gypsum, suffer from short improvement cycles, high costs, and prone to compaction. Among existing technologies, CN107384431A utilizes straw and humus, but these methods have limited salt absorption capacity. CN113308254A utilizes industrial waste residue, but this approach fails to address long-term effectiveness and resource utilization.

[0003] my country's wet processing mines generate a large amount of solid waste, including stone dust and mud cake, annually. For example, a construction stone mine in Zhoushan City, Zhejiang Province, produces approximately 1 million tons of stone dust and 500,000 tons of mud cake annually. Traditional landfill disposal is costly and polluting. Stone dust is rich in silica and aluminum oxides, which have ion exchange potential; mud cake contains clay minerals and trace nutrients, which can improve soil water retention. However, direct application of unactivated mining waste easily leads to compaction and low activity, necessitating technological innovation for its efficient utilization. Summary of the Invention

[0004] (1) Technical issues to be solved

[0005] In response to the shortcomings of the existing technology, the present invention provides a composite saline-alkali land improver based on mining solid waste. Through the synergistic effects of stone powder activation, mud cake functionalization and biochar, it can achieve pH adjustment of saline-alkali land, sodium ion adsorption and soil organic matter improvement, while realizing the resource utilization of mining solid waste.

[0006] (2) Technical solution

[0007] In order to achieve the above objectives, the main technical solutions adopted by the present invention include:

[0008] A mine solid waste-based composite saline-alkali land improver, characterized by comprising the following components in parts by weight:

[0009] F1: 50-70 parts of porous granules of activated fossil powder;

[0010] F2: 20-30 parts of rice husk-based biochar;

[0011] F3: 10-20 parts of humic acid chelated magnesium calcium powder;

[0012] F4: 3 to 5 parts of composite adhesive.

[0013] A mine solid waste-based composite saline-alkali land improver, characterized by:

[0014] The porous particles of activated fossil powder in component F1 are derived from wet-process mud cake or dry-process stone powder from volcanic rock mines, as well as solid waste remaining after mechanical crushing and screening of stripping materials or tailings. The particle size after mechanical crushing and screening is ≤0.15mm. The volcanic rock is mainly composed of volcanic debris, including volcanic debris lava rocks that transition to lava and volcanic debris sedimentary rocks that transition to sedimentary rocks. Rocks in which volcanic debris accounts for more than 90% are called volcanic debris. The volcanic debris rocks mentioned in the present invention include agglomerates, volcanic breccias, and tuffs. Because the magma ejected from volcanoes is acidic and rich in silica, volcanic debris powder has ample potential for improving saline-alkali land. The stone powder must undergo chemical composition testing to ensure that its heavy metal (As, Cd, Pb) content meets the limits of the "Soil Environmental Quality Agricultural Land Soil Pollution Risk Management Standard" (GB 15618-2018).

[0015] The rice husk-based biochar in component F2 is prepared by aerobic fermentation of rice husks inoculated with a composite bacterial agent followed by carbonization.

[0016] The humic acid chelated magnesium calcium powder in component F3 is obtained by loading a humic acid calcium magnesium complex on discarded shells after acid activation, crushing and drying; the discarded shells are selected from mussel shells.

[0017] The above-mentioned mining solid waste, rice husks, mussel shells and other waste materials are easy to obtain in Zhejiang area, and the production cost of the soil conditioner is low, and no additional cost is required.

[0018] The binder in component F4 is selected from at least one of molasses, bentonite, humic acid, sodium alginate, polyvinyl alcohol or protein glue.

[0019] Preferably, all binders can be environmentally friendly natural products or recycled industrial waste that is harmless to nature and humans, or modified to make them controllably degradable. After being applied as modifier auxiliary materials, they can be naturally degraded in the soil without producing any toxic substances. Molasses is a by-product of the sugar industry, obtained after the sugar solution is concentrated and crystallized to precipitate sugar during the sugar-making process; bentonite is a non-metallic mineral with montmorillonite as the main mineral component, and often appears as a by-product in clay mines; humic acid is a type of organic matter accumulated through the decomposition and transformation of animal and plant remains and geological action, and can be produced by fermentation of organic solid waste such as straw and cotton stalks; sodium alginate is a by-product of the extraction of iodine and mannitol from kelp or giant kelp of the brown algae class, and has the stability, solubility, viscosity and safety required for pharmaceutical preparation excipients; polyvinyl alcohol can choose oligomeric polyvinyl alcohol, or use oxidative pretreatment or the addition of composite photosensitizers to achieve controllable degradation of polyvinyl alcohol to reduce residues; protein glue, as a natural adhesive, has significant advantages in environmental protection, safety and biocompatibility, and can be extracted from leather waste scraps and waste silk.

[0020] The invention also discloses a preparation method of the saline-alkali land improving agent.

[0021] A method for preparing a mine solid waste-based composite saline-alkali land improver, characterized by comprising the following steps:

[0022] S1: Stone powder or mud cake is activated and mixed with a binder to form porous particles of activated stone powder;

[0023] S2: Rice husks are inoculated with a composite bacterial agent, aerobically fermented and then carbonized to obtain rice husk-based biochar;

[0024] S3: Shell powder is activated with oxalic acid, chelated with humic acid magnesium calcium solution, and dried and crushed to obtain humic acid chelated magnesium calcium powder;

[0025] S4: Mix the product of steps S1-S3 with the remaining binder and extrude into a granular product.

[0026] A mine solid waste-based composite saline-alkali land improver, characterized in that in step S1:

[0027] The activation treatment conditions are as follows: mixing stone powder or mud cake with 5-10% oxalic acid solution at a solid-liquid ratio of 1:3 in an acid-resistant reactor; treating with ultrasound at a frequency of 40 kHz for 1 hour at 60° C. to promote the dissolution and activation of silicon-aluminum oxide in the stone powder or mud cake; filtering and washing with deionized water until the pH value of the filtrate is ≥6.0; drying in a 60° C. forced air drying oven to a moisture content of ≤5%, and pulverizing through a 100-mesh sieve for later use;

[0028] The conditions for the puffing treatment are as follows: the binder is added with water to form a slurry with a viscosity of 2000 to 3000 mPa·s, the activated rock powder and the binder are uniformly mixed in a mass ratio of 9:1, and the mixture is placed in a feeder for puffing treatment; the puffing method is selected from any one of hot air puffing, steam flash puffing, microwave puffing or screw extrusion puffing.

[0029] A method for preparing a pyroclastic rock-rice husk composite saline-alkali land conditioner, characterized by:

[0030] The conditions of the hot air puffing method are: temperature 140-200° C., time 15-30 min; preferably, temperature 160° C., time 20 min.

[0031] The conditions of the steam flash puffing method are: steaming pressure 0.2-0.8 MPa, steaming time 5-30 min, flash pressure relief time ≤ 5 s; preferably, steaming pressure 0.5 MPa, steaming time 20 min.

[0032] The conditions of the microwave puffing method are: power 300-500W for 2 minutes in the heating stage, power 750-900W for 2.5-4 minutes in the puffing stage; preferably, power 400W for 4 minutes in the heating stage, power 800W for 4 minutes in the puffing stage.

[0033] The conditions of the screw extrusion puffing method are: feed section temperature 75-85°C, compression section temperature 115-125°C, melting section temperature 145-155°C, screw speed 200-250rpm, die aperture 4-5mm, aspect ratio (3-4):1, and die pressure 4-5MPa; preferably, feed section temperature 80°C, compression section temperature 120°C, melting section temperature 150°C, screw speed 220rpm, die aperture 5mm, aspect ratio 3:1, and die pressure 5MPa.

[0034] Preferably, the porous particles after granulation are sieved and the average particle size is 4 mm.

[0035] A method for preparing a mine solid waste-based composite saline-alkali land improver, characterized in that in step S2:

[0036] The composite bacterial agent is a compound bacterial agent of halogen-tolerant Bacillus and actinomycetes, with a weight ratio of (2-3):1, and the bacterial agent activity (determined by plate count method) is ≥1×10^8 CFU / g; preferably, the weight ratio of halogen-tolerant Bacillus and actinomycetes is 2:1.

[0037] Eastern Zhejiang (Ningbo, Zhoushan, etc.) is the main rice-producing area in Zhejiang Province, with an annual rice husk output exceeding one million tons, and has significant local advantages. Rice husks are rich in cellulose, hemicellulose and silica. Their high organic matter content provides sufficient carbon source for halotolerant Bacillus and actinomycetes, and the natural porous skeleton formed by silica can improve the stability of biochar. Halotolerant Bacillus efficiently decomposes cellulose in rice husks by secreting salt-tolerant cellulase, generating reducing sugars for bacterial metabolism; actinomycetes target the degradation of lignin, release phenolic substances and inhibit the growth of miscellaneous bacteria, ensuring the efficiency and stability of the fermentation system. Experiments show that after 72 hours of rice husk fermentation, the cellulose degradation rate reached 42%, and the lignin degradation rate reached 25%.

[0038] The aerobic fermentation conditions are as follows: crushing the rice husks to a particle size of ≤2 mm, adjusting the initial moisture content to 60% to 65%, inoculating the composite bacterial agent at 8% of the dry weight of the rice husks, uniformly mixing, and stacking in a closed fermentation tank; fermentation temperature of 45 to 50° C., fermentation cycle of 72 hours, maintaining an oxygen concentration of ≥15%, and ventilation volume of 0.5 L / (min·kg);

[0039] Preferably, the fermentation time is 72 hours. To ensure sufficient degradation of polysaccharides, the fermentation time must be maintained. Experiments have shown that the reducing sugar content reaches its peak at 72 hours. An initial moisture content of 65-70% in rice husk is beneficial for bacterial inoculant attachment.

[0040] A method for preparing a mine solid waste-based composite saline-alkali land improver, characterized in that in step S2:

[0041] The carbonization method is selected from any one of a tubular furnace carbonization method, a rotary kiln carbonization method or a microwave carbonization method.

[0042] A method for preparing a mine solid waste-based composite saline-alkali land improver, characterized by:

[0043] The conditions of the tubular furnace carbonization method are as follows: nitrogen protective gas flow rate 50 mL / min, heating rate 10 ° C / min to 500 ° C, keeping warm for 2 hours and then cooling naturally;

[0044] The conditions of the rotary kiln carbonization method are: temperature 480-520°C, residence time 2h, and water cooling after discharge;

[0045] The conditions of the microwave carbonization method are: microwave power of 800-1000W, carbonization time of 30-40min, and rapid cooling after discharge.

[0046] The purpose of carbonization is to convert fermented organic matter into stable porous carbon materials, enhance ion exchange capacity; fix the carbon structure, generate hierarchical pores (micropores + mesopores), increase specific surface area, and extend the soil improvement cycle. The test found that after carbonization, the specific surface area of rice husk-based biochar is ≥1100m 2 / g, porosity ≥85%, sodium ion adsorption capacity increased by 35% (up to 70 mg / g), and the slow release of silica can enhance the soil aggregate structure and reduce the risk of saline-alkali floor hardening.

[0047] The three carbonization methods have different advantages: the tubular furnace carbonization method has precise temperature control and no waste gas emissions, making it suitable for small-scale production of high-precision products; the rotary kiln carbonization method has a large processing capacity and low energy consumption; the microwave carbonization method is energy-saving and has a more uniform pore structure, making it suitable for products with higher requirements on appearance.

[0048] A method for preparing a mine solid waste-based composite saline-alkali land improver, characterized in that in step S3:

[0049] The preparation method of the humic acid chelated magnesium calcium freeze-dried powder is as follows: dissolving humic acid in deionized water to a concentration of 5% (w / v), adjusting the pH to 7.0 with NaOH, adding CaCl2 and MgCl2 at a molar ratio of Ca2+:Mg2+=2:1, stirring at 50°C and 300 rpm for 4 hours, filtering the reaction solution through a 0.45 μm filter membrane, and then freeze-drying to obtain the humic acid chelated magnesium calcium freeze-dried powder;

[0050] The chelation conditions are as follows: activated shell powder and humic acid chelated magnesium calcium freeze-dried powder are mixed in a weight ratio of 1:5, subjected to 40kHz ultrasonic treatment for 30 minutes, and then oscillated and adsorbed at 25°C and 150rpm for 4 hours, dried at 60°C to constant weight, and crushed to a particle size of ≤0.2mm to obtain humic acid chelated magnesium calcium powder.

[0051] Oxalic acid activation has the following effects: oxalic acid dissolves the CaCO₃ in shells, exposing the microporous structure of the shell's inner layer, increasing the surface hydroxyl content and significantly boosting the specific surface area. The preparation of a freeze-dried powder of humic acid-chelated magnesium calcium provides a stable source of calcium and magnesium ions. Furthermore, the colloidal properties of humic acid enhance soil aggregate stability. The carboxyl and phenolic hydroxyl groups of humic acid form five-membered ring chelates with calcium and magnesium ions. After chelation, the complexes reduce water solubility, enhance sustained release, and improve thermal stability. Calcium and magnesium humate are loaded into the porous structure of shell powder to achieve sustained and targeted release of calcium and magnesium ions. The alkalinity of shell powder neutralizes the acidity of humic acid, preventing its rapid release and potential damage to the soil environment. Slow-release experiments have shown that the release period of calcium and magnesium ions in soil is much longer than with direct application.

[0052] The invention also discloses the application of the saline-alkali land improver in improving alkaline soil.

[0053] Application of a mine solid waste-based composite saline-alkali land improver in saline-alkali land improvement, characterized by:

[0054] The amendment is evenly spread at a rate of 80-200 kg / mu and mixed with the surface soil. It is suitable for coastal saline-alkali land with pH ≥ 8.5 or EC ≥ 4dS / m.

[0055] Preferably, different application plans should be formulated for soils with different salinization conditions: mild salinization (EC 4-6dS / m): application rate 50-100kg / mu, single application; moderate salinization (EC 6-8dS / m): application rate 150-200kg / mu, two applications with an interval of 30 days; severe salinization (EC>8dS / m): application rate 200kg / mu, and auxiliary leaching measures (such as drip irrigation system) should be added.

[0056] (3) Beneficial effects

[0057] The beneficial effects of the present invention are:

[0058] 1. The saline-alkali soil conditioner prepared by a special process in the present invention mainly uses volcanic debris rock powder (high silicon and aluminum content) to absorb sodium ions through ion exchange, rice husk fermentation charcoal (porous structure) to increase soil organic matter and fix salt, and humic acid chelated magnesium calcium powder to neutralize alkalinity. The three work together to achieve long-term improvement of salt adsorption, organic matter replenishment, and acid-base balance. It not only effectively reduces soil bulk density and soil hardness, increases soil porosity and permeability, thereby improving soil structure; it also analyzes soil physical and chemical properties such as soil pH, nitrogen, phosphorus, and potassium, and specifically improves soil pH, effectively increases the content of available phosphorus, fast-acting potassium, and organic matter in the soil, and improves soil conductivity.

[0059] 2. The raw materials used in the preparation method of the present invention, including waste stone powder, discarded shells, and aquatic product scraps, are all natural ingredients. Using these raw materials to prepare saline-alkali soil conditioners not only solves the problem of waste resources, turning waste into valuables, but also effectively improves soil conditions without causing secondary damage to the soil environment. The raw materials are widely available, safe and environmentally friendly, low-cost, and have a wide range of applications. They offer good economic and environmental benefits and can be used on a large scale.

[0060] 3. Each ton of this amendment can dispose of approximately 500kg of volcanic rock dust, 450kg of rice husks, and 150kg of shells, significantly reducing CO2 emissions compared to traditional landfills while also generating additional income for local farmers. This amendment can also be used to formulate vegetation substrates in saline-alkali land restoration projects. When used in combination with salt-tolerant plants (such as Suaeda salsa and Tamarix chinensis), it can improve survival rates. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] The present invention is described with the aid of the following drawings:

[0062] Figure 1 This is a physical diagram according to Example 1 of the present invention. DETAILED DESCRIPTION

[0063] To make the objectives, technical solutions, and effects of the present invention more clear and explicit, the present invention is further described in detail below with reference to the following examples and accompanying drawings. However, it should be understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention. In the present invention, unless otherwise specified, all equipment and raw materials can be purchased from the market or are commonly used in the industry. The methods in the following examples, unless otherwise specified, are all conventional methods in the art.

[0064] Example 1

[0065] A tuff-rice husk composite saline-alkali land improver, characterized by comprising the following components in parts by weight:

[0066] F1: 60 parts of tuff (wet-process mud cake) activated rock powder porous granules;

[0067] F2: 25 parts of rice husk-based biochar;

[0068] F3: 12 parts of humic acid chelated magnesium calcium powder;

[0069] F4: 3 parts of sodium alginate-bentonite (weight ratio 1:1) binder;

[0070] A method for preparing a tuff-rice husk composite saline-alkali land conditioner, characterized by comprising the following steps:

[0071] S1: The wet mud cake was mixed with 8% oxalic acid solution at a solid-liquid ratio of 1:3, ultrasonically treated at 60°C for 1 hour, washed, dried, and then crushed to a particle size of ≤0.15 mm. The stone powder was mixed with half of the binder. Because sodium alginate easily forms a gel when it comes into contact with water, it was quickly and evenly heated and expanded using microwaves to form porous particles. This prevented thermal degradation of the binder and ensured uniform particle pores. The expansion conditions were a power of 400 W for 2 minutes in the heating stage and a power of 800 W for 3 minutes in the expansion stage.

[0072] S2: Rice husks were inoculated with a composite bacterial agent with a weight ratio of halophilic bacteria to lactic acid bacteria of 2:1, and aerobically fermented at 45°C for 72 hours. Rice husk fermentation charcoal was obtained using a tubular furnace carbonization method. The carbonization conditions were: 500°C for 2 hours under nitrogen protection. The tubular furnace has precise temperature control and is suitable for small-scale production of high-purity biochar.

[0073] S3: Mussel shell powder is activated with 10% oxalic acid, chelated with magnesium calcium humate solution, and dried and crushed to ≤0.2mm;

[0074] S4: The products of steps S1-S3 are mixed with the remaining binder, and after mixing, granulated using a screw extruder (die head pressure 5 MPa) with a granule diameter of 4 mm to produce granule product A1.

[0075] The application of saline-alkali land improver A1 in saline-alkali land improvement is characterized by:

[0076] Evenly spread the soil conditioner into the soil to be improved and mix it with the surface soil at a rate of 150 kg / mu. This example is suitable for small-scale production of high-purity soil conditioner. Microwave expansion and sodium alginate synergistically enhance the granules' water absorption and fertilizer retention, making it suitable for seasonally arid soils in eastern Zhejiang.

[0077] Example 2

[0078] A volcanic breccia-rice husk composite saline-alkali land improver, characterized by comprising the following components in parts by weight:

[0079] F1: 50 parts of porous granules of breccia (dry stone powder);

[0080] F2: 30 parts of rice husk-based biochar;

[0081] F3: Humic acid chelated magnesium calcium powder 20 parts;

[0082] F4: 5 parts of molasses-humic acid (weight ratio 2:1) binder.

[0083] A method for preparing a volcanic breccia-rice husk composite saline-alkali land conditioner, characterized by comprising the following steps:

[0084] S1: Dry stone powder is activated with 5% oxalic acid solution and then crushed through a 100-mesh sieve. Steam flash puffing is used with a steaming pressure of 0.5 MPa / 20 min and flash pressure relief of ≤5 s. Molasses has low viscosity, and steam puffing can avoid high-temperature coking. Steam penetration also enhances particle porosity.

[0085] S2: Rice husks were inoculated with a composite bacterial agent, with a weight ratio of halophilic bacteria to lactic acid bacteria of 2:1, and aerobically fermented at 45°C for 72 hours. Rice husk fermentation charcoal was obtained using a rotary kiln carbonization method. The carbonization conditions were: 500°C for 2 hours under nitrogen protection. The rotary kiln has a large processing capacity, suitable for large-scale continuous production of molasses binder, and has high carbonization efficiency.

[0086] S3: Same as Example 1, particle size ≤ 0.2 mm;

[0087] S4: The products of steps S1-S3 are mixed with the remaining binder, and after mixing, granulated using a ring die granulator with a granule diameter of 5 mm to produce granule product A2.

[0088] The application of saline-alkali land improver A2 in saline-alkali land improvement is characterized by:

[0089] The soil conditioner is evenly spread on the soil to be improved and mixed with the surface soil at a rate of 200 kg / mu. The molasses binder in this soil conditioner is low in cost and contains natural sugars that can stimulate soil microbial activity, making it potentially suitable for large-scale production.

[0090] Example 3

[0091] A volcanic agglomerate rock-rice husk composite saline-alkali land improver, characterized by comprising the following components in parts by weight:

[0092] F1: 70 parts of porous granules of activated rock powder from agglomerate rock (tailings);

[0093] F2: 20 parts of rice husk-based biochar;

[0094] F3: 10 parts of humic acid chelated magnesium calcium powder;

[0095] F4: 4 parts of polyvinyl alcohol (oligomeric type) binder.

[0096] A method for preparing a volcanic agglomerate rock-rice husk composite saline-alkali land conditioner, characterized by comprising the following steps:

[0097] S1: After the tailings ore is crushed, it is activated with 10% oxalic acid solution and dried to a moisture content of ≤5%. The pellets are extruded using a screw extrusion method with a temperature gradient of 80°C → 120°C → 150°C and a die pressure of 5 MPa. Polyvinyl alcohol requires high temperature plasticization, and the screw extrusion method provides stable hot melt conditions to ensure the mechanical strength of the pellets.

[0098] S2: Rice husks were inoculated with a composite bacterial agent, with a weight ratio of halophilic bacteria to lactic acid bacteria of 3:1, and aerobically fermented at 45°C for 72 hours. Rice husk fermentation charcoal was obtained using microwave carbonization. Carbonization conditions were 900W microwave power, 35 minutes carbonization time, and rapid cooling after discharge. Microwave carbonization resulted in uniform pore distribution, meeting the high structural stability requirements of polyvinyl alcohol particles.

[0099] S3: Same as Example 1, particle size ≤ 0.2 mm;

[0100] S4: The products of steps S1-S3 are mixed with the remaining binder, and after mixing, granulation is performed using a twin-screw extruder. The granules have a diameter of 5 mm, and granular product A2 is obtained.

[0101] The application of saline-alkali land improver A3 in saline-alkali land improvement is characterized by:

[0102] The soil conditioner is evenly spread on the soil to be improved and mixed with the surface soil at an application rate of 100 kg / mu. This soil conditioner has a smooth granular surface and strong weather resistance, making it suitable for rainy areas or heavily saline-alkali land that requires long-term improvement.

[0103] Comparative Example 1

[0104] The preparation process was essentially the same as in Example 1, except that the mine waste stone powder was not granulated, and 60 parts by weight of mine waste stone powder was used directly instead of an equal mass of stone powder particles with an average particle size of 4 mm. In this case, the saline-alkali soil conditioner D1 was prepared.

[0105] Comparative Example 2

[0106] The preparation process is substantially the same as that of Example 1, except that the fermented rice husk charcoal in step S2 is replaced with unfermented and carbonized rice husk. At this point, the saline-alkali soil conditioner D2 is prepared.

[0107] Comparative Example 3

[0108] The preparation process is basically the same as that of Example 1, except that the humic acid chelated magnesium calcium powder is replaced with unactivated and chelated shell powder in step S3. At this time, the saline-alkali soil conditioner D3 is prepared.

[0109] Soil improvement tests were carried out using the products of the above examples and comparative examples to verify their performance.

[0110] The soil samples were collected from blank plots without crops. After the collected soil samples were naturally air-dried, stones and other debris were removed. After passing through a 2mm nylon sieve, they were placed in self-sealing bags and stored at 4°C for future use.

[0111] Blank soil was used in potting pots, with each pot filled with 3 kg of soil. Three replicates were set up, and the soil was evenly mixed with the soil amendment before potting. Deionized water was added every 2–4 days during the experiment, and the soil moisture content was maintained at 20% by weighing, ensuring the soil surface was slightly moist. On the 25th day after the experimental treatment, soil samples were collected by vertically inserting a 300 mm long, 15 mm diameter cylindrical auger into the soil. Five random samples were taken from each pot, and the pH and basic chemical properties of the soil samples were tested.

[0112] (1) Effects of different soil conditioners on soil pH

[0113] Soil pH, also known as soil acidity and alkalinity, is one of the important basic properties of soil and an indicator of soil formation and maturation and fertilization. Various plants have their own suitable pH range, and their growth will be hindered if it exceeds this range. According to the zonal distribution of soil in my country, it is more appropriate to divide soil acidity and alkalinity into five levels for practical application. The five levels of pH are: strongly acidic (pH <5.0), acidic (pH = 5.0-6.5), neutral (pH = 6.5-7.5), alkaline (pH = 7.5-8.5), and strongly alkaline (pH ≥ 8.5).

[0114] Table 1 Effects of different soil amendments on soil pH

[0115]

[0116] After the amendment was applied to the soil, the soil pH changed at different levels.

[0117] (2) Effects of different soil conditioners on soil nutrients

[0118] Soil EC refers to soil electrical conductivity. Soil EC is an indicator for measuring soil water-soluble salts, which are an important indicator of inorganic nutrients in the surface soil that can be quickly utilized by plants. It is a factor in determining whether salt ions in the soil are limiting crop growth. EC values generally range from 0.4 to 2. Excessively high soluble salt content (EC value) in the substrate can create reverse osmotic pressure, displacing water from the roots and causing the root tips to turn brown or dry out. Fluctuations in substrate humidity can further exacerbate the problem of excessive soluble salt content, severely damaging the plant's root system and preventing it from absorbing water and nutrients. This can lead to symptoms such as wilting, chlorosis, tissue necrosis, or stunted growth. Excessively high EC values can also increase the incidence of root rot caused by cotton rot pathogens.

[0119] Table 2 Effects of different soil conditioners on soil nutrients

[0120]

[0121] After the amendment was added to the soil, soil nutrients changed. Compared with unamended soil, the addition of the amendment improved the electrical conductivity of the soil. With the addition of the amendment, the available phosphorus content in the soil of each example was significantly improved, and the value of the comparative example also increased. Compared with the blank group, the organic matter content showed an upward trend with the addition of the amendment.

[0122] (3) Effects of different soil conditioners on soil aeration

[0123] Soil aeration was determined using the ring knife method: soil samples were collected using the ring knife method. The S-shaped sampling method was used in the standard plot to select the soil layer with relatively consistent environmental factors and mark them for the determination of soil physical properties. The sampling was repeated three times.

[0124] Table 3 Effects of different soil conditioners on soil aeration

[0125]

[0126]

[0127] (4) Effect of weathering resistance of different soil conditioners

[0128] The soil amendment was placed in different environments to test its weatherability: ① Using a curing chamber to simulate a high-temperature, high-humidity environment at 60°C ± 2°C and 90% ± 5% humidity for 120 hours; ② Using a refrigerator to simulate a low-temperature, high-humidity environment at -10°C ± 2°C and 10% ± 5% humidity for 120 hours; ③ Using a curing chamber and a refrigerator to simulate a freeze-thaw cycle, freezing at -10°C ± 2°C for 12 hours and thawing at 25°C ± 2°C for 12 hours, repeated five times; and ④ Soaking in a saline solution (5% NaCl + 3% NaHCO3) at a pH of 9.0 ± 0.5 for 120 hours to simulate saline-alkali stress. Grain integrity was comprehensively evaluated using weighing and observing surface cracks.

[0129] Table 4 Effect of different soil conditioners on weather resistance

[0130]

[0131] Compared with the blank group, different bonding methods have a significant impact on the weather resistance of the modifier. Polyvinyl alcohol adhesives are suitable for rainy areas or severely saline-alkali lands and have high durability. Molasses-humic acid adhesives have the advantage of low cost and can be applied on a large scale. Sodium alginate-bentonite adhesives are suitable for arid areas and areas that require rapid water absorption and fertilizer retention.

[0132] In summary, Examples 1, 2, and 3 can play an optimal role in improving saline-alkali soil. They can not only effectively reduce the pH of saline-alkali soil, but also play the role of stone powder particles, shells, and rice husks in the soil as a skeleton support. As a better soil fluffy structure, they can also effectively increase the contact area between active ingredients and soil, thereby better completing the delivery of nutrients.

[0133] It should be understood that the above description of the specific embodiments of the present invention is merely for the purpose of illustrating the technical approach and features of the present invention. Its purpose is to enable those skilled in the art to understand the contents of the present invention and implement them accordingly. However, the present invention is not limited to the above-described specific embodiments. Any changes or modifications made within the scope of the claims of the present invention are intended to be covered by the scope of protection of the present invention.

Claims

1. A mine solid waste-based composite saline-alkali land improver, characterized in that: It comprises the following components in parts by weight: F1: 50-70 parts of porous granules of activated fossil powder; F2: 20-30 parts of rice husk-based biochar; F3: 10-20 parts of humic acid chelated magnesium calcium powder; F4: 3 to 5 parts of composite adhesive.

2. The saline-alkali land improving agent according to claim 1, characterized in that: The porous particles of activated fossil powder in component F1 are derived from the solid waste remaining after mechanical crushing and screening of wet-process mud cake or dry-process stone powder and stripping material or tailings of volcanic rock mines, with a particle size of ≤0.15 mm; The rice husk-based biochar in component F2 is prepared by aerobic fermentation of rice husks inoculated with a composite bacterial agent followed by carbonization; The humic acid chelated magnesium calcium powder in component F3 is prepared by loading humic acid calcium magnesium complex with discarded shells after acid activation, crushing and drying; the discarded shells are selected from mussel shells; The binder in component F4 is selected from at least one of molasses, bentonite, humic acid, sodium alginate, polyvinyl alcohol or protein glue.

3. A method for preparing the saline-alkali land improver according to any one of claims 1 to 2, characterized in that: The following steps are involved: S1: Stone powder or mud cake is activated and mixed with a binder to form porous particles of activated stone powder; S2: Rice husks are inoculated with a composite bacterial agent, aerobically fermented and then carbonized to obtain rice husk-based biochar; S3: Shell powder is activated with oxalic acid, chelated with humic acid magnesium calcium solution, and dried and crushed to obtain humic acid chelated magnesium calcium powder; S4: Mix the products of steps S1-S3 with a binder and extrude them into granular products.

4. The preparation method according to claim 3, characterized in that In step S1: The activation treatment conditions are as follows: mixing stone powder or mud cake with 5-10% oxalic acid solution at a solid-liquid ratio of 1:3 in an acid-resistant reactor; treating with ultrasound at a frequency of 40 kHz for 1 hour at 60° C. to promote the dissolution and activation of silicon-aluminum oxide in the stone powder or mud cake; filtering and washing with deionized water until the pH value of the filtrate is ≥6.0; drying in a 60° C. forced air drying oven to a moisture content of ≤5%, and pulverizing through a 100-mesh sieve for later use; The conditions for the puffing treatment are as follows: the binder is added with water to form a slurry with a viscosity of 2000 to 3000 mPa·s, the activated rock powder and the binder are uniformly mixed in a mass ratio of 9:1, and the mixture is placed in a feeder for puffing treatment; the puffing method is selected from any one of hot air puffing, steam flash puffing, microwave puffing or screw extrusion puffing.

5. The preparation method according to claim 4, characterized in that: The conditions of the hot air puffing method are: temperature 140-200°C, time 15-30 minutes; The conditions of the steam flash puffing method are: steaming pressure 0.2-0.8 MPa, steaming time 5-30 min, flash pressure relief time ≤ 5 s; The microwave puffing method is as follows: the power of the heating stage is 300-500W, the time is 2 minutes, and the power of the puffing stage is 750-900W, the time is 2.5-4 minutes; The conditions of the screw extrusion puffing method are: feed section temperature 75-85°C, compression section temperature 115-125°C, melting section temperature 145-155°C, screw speed 200-250rpm, die aperture 4-5mm, aspect ratio (3-4):1, and die pressure 4-5MPa.

6. The preparation method according to claim 3, characterized in that In step S2: The composite bacterial agent is a compound bacterial agent of halodurable Bacillus and actinomycetes, with a weight ratio of (2-3):1, and the bacterial agent activity (determined by plate count method) is ≥1×10^8 CFU / g; The aerobic fermentation conditions are as follows: crushing the rice husks to a particle size of ≤2 mm, adjusting the initial moisture content to 60%-65%, inoculating the composite bacterial agent at 8% of the dry weight of the rice husks, uniformly mixing, and stacking in a closed fermentation tank; fermentation temperature of 45-50°C, fermentation cycle of 72 hours, maintaining an oxygen concentration of ≥15%, and ventilation volume of 0.5 L / (min·kg).

7. The preparation method according to claim 3, characterized in that In step S2: The carbonization method is selected from any one of a tubular furnace carbonization method, a rotary kiln carbonization method or a microwave carbonization method.

8. The preparation method according to claim 7, characterized in that: The conditions of the tubular furnace carbonization method are as follows: nitrogen protective gas flow rate 50 mL / min, heating rate 10 ° C / min to 500 ° C, keeping warm for 2 hours and then cooling naturally; The conditions of the rotary kiln carbonization method are: temperature 480-520°C, residence time 2h, and water cooling after discharge; The conditions of the microwave carbonization method are: microwave power of 800-1000W, carbonization time of 30-40min, and rapid cooling after discharge.

9. The preparation method according to claim 3, characterized in that In step S3: The preparation method of the humic acid chelated magnesium calcium freeze-dried powder is as follows: dissolving humic acid in deionized water to a concentration of 5% (w / v), adjusting the pH to 7.0 with NaOH, and 2+ :Mg 2+ =2:1 molar ratio of CaCl2 and MgCl2, stirred at 50 ° C, 300 rpm for 4 h, the reaction solution was filtered through a 0.45 μm filter membrane and freeze-dried to obtain humic acid chelated magnesium calcium freeze-dried powder; The chelation conditions are as follows: activated shell powder and humic acid chelated magnesium calcium freeze-dried powder are mixed in a weight ratio of 1:5, subjected to 40kHz ultrasonic treatment for 30 minutes, and then oscillated and adsorbed at 25°C and 150rpm for 4 hours, dried at 60°C to constant weight, and crushed to a particle size of ≤0.2mm to obtain humic acid chelated magnesium calcium powder.

10. Use of the saline-alkali land improving agent according to any one of claims 1 to 2 in improving saline-alkali land, characterized in that: The improver is evenly spread into the soil to be improved and mixed with the surface soil at an application rate of 50 to 200 kg per mu; the saline-alkali land is soil with a pH of ≥8.5 or an electrical conductivity (EC) of ≥4 dS / m.

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