Pyroclastic rock-seaweed residue composite saline-alkali soil modifier as well as preparation method and application thereof

Abstract

The invention discloses a pyroclastic rock-seaweed residue composite saline-alkali soil modifier as well as a preparation method and application thereof, and belongs to the technical field of soil remediation. The modifier is prepared from volcanic rock solid waste, seaweed residues and shells as raw materials through stone powder puffing granulation, microbial fermentation carbonization and calcium magnesium humate chelation modification of shell powder and comprises 40-60 parts of volcanic clastic rock powder, 20-30 parts of seaweed residue fermented carbon, 10-20 parts of modified shell powder and 3-5 parts of a binder. During preparation, the rock powder and the binder are mixed and puffed; carrying out anaerobic fermentation on the seaweed residue inoculated microbial inoculum, and then carbonizing; the shell powder is activated by citric acid, chelated with the humic acid chelated magnesium calcium freeze-dried powder, dried and crushed, and then mixed with the product and a binder for extrusion forming. The modifier is applied to soil according to 50-200 kg / mu and mixed with the surface layer, the pH can be reduced, sodium ions can be adsorbed, the nutrition and ventilation rate can be improved, the durability is high, and the modifier is suitable for coastal salinized soil treatment.

Description

Technical Field

[0001] The present invention relates to the technical field of soil improvement, and in particular to a composite saline-alkali land improver using pyroclastic rock mine solid waste and seaweed processing waste as raw materials and a preparation method thereof, which is suitable for soil remediation of coastal saline-alkali land and salinized farmland. Background Art

[0002] Soil is the basis for plant growth, and the quality level of soil will directly affect the soil ecosystem and thus the growth and development of plants. Saline-alkali soil seriously restricts agricultural production due to problems such as high salt, high sodium, and low organic matter. Traditional amendments (such as gypsum and desulfurized gypsum) mainly reduce the sodium adsorption ratio (SAR) by replacing sodium ions with calcium ions, but have the following defects: the saline-alkali land amendment disclosed in the Chinese patent document with application publication number CN107384431A relies on straw and humus, has limited salt adsorption capacity, and is prone to soil compaction. A saline-alkali land amendment is disclosed in the Chinese patent document with application publication number CN113308254A, which uses industrial waste residues such as dealuminated red mud powder, but does not solve the problems of material recovery and long-term effectiveness.

[0003] The Dahuangshan building stone mine on Cezi Island in Zhoushan City, Zhejiang Province, has a reserve of approximately 200 million tons. Due to the wet processing of building stone at the mine, the stone dust content is approximately 5%, and the stone dust volume is approximately 10 million tons, with an annual output of approximately 1 million tons. Currently, most domestic mines of the same type that use wet mining methods adopt a disposal method of transporting the stone to a different location and landfilling it. This results in high disposal costs (at a current processing fee of approximately 30 yuan per ton, the annual stone dust disposal cost is approximately 30 million yuan, and the total disposal cost is approximately 300 million yuan). This leads to a heavy environmental burden, wastes resources, occupies land, and causes environmental pollution. For these reasons, the comprehensive utilization of waste mine stone dust is extremely necessary. However, existing technologies (such as CN107384430A) simply carbonize the stone dust, failing to fully utilize its ion exchange potential.

[0004] According to the 2024 Zhoushan Statistical Yearbook, Zhoushan's annual aquatic product output reached 1,956,235 tons in 2023, of which algae aquaculture produced 10,021 tons, and shellfish and cephalopod processing exceeded 900,516 tons. This generated over 10,000 tons of seafood waste annually. This waste primarily consists of organic solid wastes such as algae residues, crustacean exoskeletons, and mollusc shells and viscera. Traditional disposal methods, primarily landfilling, incineration, or ocean dumping, have exposed significant environmental and economic issues. Therefore, the development of efficient and environmentally friendly seafood waste recycling technologies has become an urgent need for the aquatic processing industry to achieve a circular economy. Summary of the Invention

[0005] (1) Technical issues to be solved

[0006] In response to the shortcomings of the existing technology, the present invention provides a pyroclastic rock-seaweed slag composite saline-alkali land improver, which achieves saline-alkali land pH adjustment, sodium ion adsorption and organic matter improvement through the synergistic action of multiple components, while reducing production costs by waste resource utilization.

[0007] (2) Technical solution

[0008] In order to achieve the above objectives, the main technical solutions adopted by the present invention include:

[0009] A pyroclastic rock-seaweed slag composite saline-alkali land improver, characterized by comprising the following components in parts by weight:

[0010] F1: 40-60 parts of pyroclastic rock powder;

[0011] F2: 20-30 parts of seaweed residue fermented charcoal;

[0012] F3: 10-20 parts of modified shell powder;

[0013] F4: 3 to 5 parts of adhesive.

[0014] A pyroclastic rock-seaweed slag composite saline-alkali land improver, characterized by:

[0015] The particle size of the pyroclastic rock powder in component F1 is ≤ 0.075 mm, and is derived from mud cake produced by wet process, stone powder produced by dry process, and solid waste remaining after mechanical crushing and screening of stripping material or tailings of volcanic rock building stone mines.

[0016] The pyroclastic rock powder is mainly composed of pyroclastic material, which is a rock type between volcanic rock and sedimentary rock. There are pyroclastic lava types that transition to lava and pyroclastic sedimentary rocks that transition to sedimentary rock. Rocks in which volcanic debris accounts for more than 90% are called pyroclastic rocks. The pyroclastic rocks mentioned in the present invention include agglomerates, volcanic breccias and tuffs. Because the magma ejected from the volcano is acidic magma rich in silica, pyroclastic rock powder has sufficient potential for improving saline-alkali land. The stone powder must be tested for chemical composition to ensure that its heavy metal (As, Cd, Pb, etc.) content meets the limit values of the "Soil Environmental Quality Agricultural Land Soil Pollution Risk Control Standard" (GB 15618-2018).

[0017] The seaweed residue fermentation charcoal in component F2 is prepared by anaerobic fermentation of seaweed residue with a composite bacterial agent followed by carbonization.

[0018] The seaweed residue is derived from waste from aquatic product processing enterprises and is selected from one or more processing wastes of large seaweeds. The large seaweeds are selected from common algae such as kelp, laver, sargassum, and wakame.

[0019] The modified shell powder in component F3 is obtained by acid-activating, crushing and drying discarded shells, and then loading them with a humic acid calcium-magnesium complex; the discarded shells are selected from oyster shells or scallop shells.

[0020] The volcanic debris rock powder, seaweed residue, discarded shells and other waste materials used above are easy to obtain in Zhejiang area. The production cost of the soil conditioner is low and no additional cost is required.

[0021] The binder in component F4 is selected from at least one of sodium carboxymethyl cellulose, sodium lignin sulfonate, molasses, bentonite, humic acid, sodium alginate, starch, polyvinyl alcohol or protein glue.

[0022] Preferably, all binders can be environmentally friendly natural products or recycled from harmless industrial waste to nature and human body, or modified to make them controllably degradable. After application as a modifier auxiliary material, they can be naturally degraded in the soil without producing toxic substances. Sodium carboxymethyl cellulose is a carboxymethyl derivative of cellulose, which can be extracted from agricultural wastes such as waste cotton, pineapple crowns and mango seed rinds; sodium lignin sulfonate is a natural high molecular polymer second only to cellulose and chitin in nature, and can be produced from wastes such as papermaking waste pulp; molasses is a by-product of the sugar industry, which is the residue left after the sugar solution is concentrated and crystalline sugar is precipitated during the sugar production 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 by the decomposition and transformation of animal and plant remains through microorganisms and geological action, and can be fermented from organic solid wastes such as straw and cotton stalks. Sodium alginate is a by-product of extracting iodine and mannitol from kelp or giant kelp of brown algae. It has the stability, solubility, viscosity and safety required for pharmaceutical preparation excipients. Starch can be extracted from production wastewater in the agricultural and sideline product processing industry (such as high-concentration starch wastewater from potatoes). As an adhesive, it has significant advantages in environmental protection, safety and cost. Polyvinyl alcohol can use oligomeric polyvinyl alcohol, or use oxidative pretreatment or add 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.

[0023] The invention also discloses a preparation method of the saline-alkali land improving agent.

[0024] A method for preparing a pyroclastic rock-seaweed slag composite saline-alkali land conditioner, characterized by comprising the following steps:

[0025] S1: Pyroclastic rock powder is mixed with a binder and expanded to form porous particles;

[0026] S2: Inoculating the seaweed residue with a composite bacterial agent, anaerobic fermentation and carbonization to obtain seaweed residue fermentation charcoal;

[0027] S3: activating the shell powder with citric acid, chelating it with humic acid chelated magnesium calcium freeze-dried powder, drying and crushing it to obtain modified shell powder;

[0028] S4: Mix the products of steps S1-S3 with a binder and extrude them into granular products.

[0029] A method for preparing a pyroclastic rock-seaweed slag composite saline-alkali land conditioner, characterized in that in step S1:

[0030] The puffing method is selected from any one of hot air puffing, steam flash puffing, microwave puffing or screw extrusion puffing.

[0031] A method for preparing a pyroclastic rock-seaweed slag composite saline-alkali land improver, characterized by:

[0032] The conditions of the hot air puffing method are: temperature 140-200° C., time 15-30 min; preferably, temperature 160° C., time 20 min.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] Preferably, the porous particles after granulation are sieved and the average particle size is 4 mm.

[0037] A method for preparing a pyroclastic rock-seaweed slag composite saline-alkali land conditioner, characterized in that in step S2:

[0038] The composite bacterial agent is a compound bacterial agent of halophilic bacteria and lactic acid bacteria, and the weight ratio of halophilic bacteria to lactic acid bacteria is (2-3):1; preferably, the weight ratio of halophilic bacteria to lactic acid bacteria is 2:1.

[0039] Halophiles can adapt to high-salt environments, decomposing complex polysaccharides (such as alginate and cellulose) in seaweed residue to produce small-molecule organic matter (such as monosaccharides and organic acids). This can improve the degradability of seaweed residue and provide a more uniform pore structure for subsequent carbonization. Lactic acid bacteria lower the pH value through lactic acid fermentation, inhibit the growth of putrefactive bacteria, reduce odor and harmful gases during the fermentation process, optimize the fermentation environment, and improve the stability of organic matter. High-salt environments require more halophiles to lead decomposition, and lactic acid bacteria assist in regulating the acid-base balance. An imbalance in the ratio will lead to a decrease in fermentation efficiency. Previous experimental data show that the polysaccharide degradation rate is highest when the weight ratio of halophiles to lactic acid bacteria is 2:1.

[0040] The conditions for the anaerobic fermentation are as follows: inoculating the composite bacterial agent at 5-10% of the dry weight of the seaweed residue, with an initial moisture content of 65-70% and a pH value of 6.5-7.0; after uniform mixing, loading into a sealed fermentation tank, and fermenting in an anaerobic environment for 70-72 hours, maintaining the pressure in the tank at 0.05-0.1 MPa and the temperature at 35-40° C. during the fermentation process.

[0041] Preferably, the fermentation time is 72 hours. To ensure sufficient degradation of polysaccharides, the fermentation time must be maintained. Experimental results show that reducing sugar content reaches its peak at 72 hours. An initial moisture content of 65-70% in seaweed residue is beneficial for bacterial attachment. The optimal growth temperature for halophiles is 35-40°C.

[0042] The anaerobic environment includes introducing an inert gas as the ambient atmosphere. The inert gas is selected from conventional types in the art, including nitrogen, helium, neon, etc.

[0043] A method for preparing a pyroclastic rock-seaweed slag composite saline-alkali land conditioner, characterized in that in step S2:

[0044] The carbonization method is selected from any one of a tubular furnace carbonization method, a rotary kiln carbonization method or a microwave carbonization method.

[0045] A method for preparing a pyroclastic rock-seaweed slag composite saline-alkali land improver, characterized by:

[0046] 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;

[0047] The conditions of the rotary kiln carbonization method are: temperature 480-520°C, residence time 2h, and water cooling after discharge;

[0048] The conditions of the microwave carbonization method are: microwave power of 800-1000W, carbonization time of 30-40min, and rapid cooling after discharge.

[0049] The purpose of carbonization is to convert fermented organic matter into stable porous carbon materials to enhance ion exchange capacity; fix the carbon structure, generate hierarchical pores (micropores + mesopores), and increase the specific surface area (≥800m 2 / g), extending the soil improvement cycle. Experiments have found that carbonization temperature is the primary factor affecting the physical and chemical properties of biochar. If the appropriate carbonization temperature is not selected, the prepared biochar will not have a rich pore structure and a wide specific surface area, ultimately reducing its effect on improving soil acidity.

[0050] 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.

[0051] A method for preparing a pyroclastic rock-seaweed slag composite saline-alkali land conditioner, characterized in that in step S3:

[0052] 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;

[0053] 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, 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 ≤0.3mm.

[0054] Citric acid activation has the following effects: citric 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.

[0055] The invention also discloses the application of the saline-alkali land improver in improving alkaline soil.

[0056] A pyroclastic rock-seaweed slag composite saline-alkali land improver is used in saline-alkali land improvement, which is characterized by:

[0057] 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 / mu; the saline-alkali land is soil with a pH of ≥8.5 or an electrical conductivity (EC) of ≥4dS / m.

[0058] 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.

[0059] (3) Beneficial effects

[0060] The beneficial effects of the present invention are:

[0061] 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, seaweed residue fermentation charcoal (porous structure) to increase soil organic matter and fix salt, and modified shell powder (calcium and magnesium slow release) 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.

[0062] 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.

[0063] 3. Each ton of this amendment can absorb 500kg of volcanic rock dust, 300kg of seaweed residue, and approximately 150kg of shells, significantly reducing CO2 emissions compared to traditional landfills. This amendment can also be used to prepare vegetation substrates for saline-alkali land restoration projects. Its use in combination with salt-tolerant plants (such as Suaeda salsa and Tamarix chinensis) can improve survival rates. BRIEF DESCRIPTION OF THE DRAWINGS

[0064] The present invention is described with the aid of the following drawings:

[0065] Figure 1 This is a physical diagram according to Example 1 of the present invention. DETAILED DESCRIPTION

[0066] 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.

[0067] Example 1

[0068] A tuff-seaweed slag composite saline-alkali land improver, characterized by comprising the following components in parts by weight:

[0069] F1: 50 parts of tuff dry stone powder;

[0070] F2: 30 parts of seaweed residue fermented charcoal;

[0071] F3: 17 parts of modified shell powder;

[0072] F4: 3 parts of sodium carboxymethyl cellulose binder.

[0073] A method for preparing a tuff-seaweed slag composite saline-alkali land improver is characterized by comprising the following steps:

[0074] S1: tuff stone powder was mixed with half of the binder and expanded using microwaves to form porous particles. The expansion conditions were a heating stage with a power of 400 W for 2 minutes and an expansion stage with a power of 800 W for 3 minutes.

[0075] S2: Inoculate seaweed residue with a composite bacterial agent, with a weight ratio of halophilic bacteria to lactic acid bacteria of 2:1. After anaerobic fermentation for 72 hours, carbonize the residue in a rotary kiln to obtain seaweed residue fermentation charcoal. The carbonization conditions are: temperature 500°C, residence time 2 hours, and water cooling after discharge.

[0076] S3: Oyster shell powder (particle size ≤ 0.3 mm) was mixed with 5% citric acid solution at a solid-liquid ratio of 1:3, activated by shaking at 25°C for 2 h, filtered, washed with water until neutral, and dried at 60°C; the activated shell powder was mixed with humic acid chelated magnesium calcium freeze-dried powder (5% w / v) at a weight ratio of 1:5, ultrasonically treated at 40 kHz for 30 min, adsorbed by shaking at 25°C for 4 h, dried at 60°C, and then crushed to a particle size ≤ 0.3 mm;

[0077] S4: Mix the products of steps S1-S3 with the remaining binder and extrude them into granular product A1.

[0078] The application of saline-alkali land improver A1 in saline-alkali land improvement is characterized by:

[0079] The improver is evenly spread on the soil to be improved and mixed with the surface soil at an application rate of 150 kg / mu. The raw materials of this soil improver are easily available, the equipment investment is low, and it is suitable for the initial promotion of saline-alkali land treatment.

[0080] Example 2

[0081] A volcanic breccia-seaweed slag composite saline-alkali land improver, characterized by comprising the following components in parts by weight:

[0082] F1: 56 parts of volcanic breccia tailings powder;

[0083] F2: 20 parts of seaweed residue fermented charcoal;

[0084] F3: 20 parts of modified shell powder;

[0085] F4: 4 parts of alginate-starch (weight ratio 1:1) binder.

[0086] A method for preparing a volcanic breccia-seaweed slag composite saline-alkali land improver is characterized by comprising the following steps:

[0087] S1: Mix volcanic breccia rock powder with half of the binder and use steam flash expansion to form porous particles. The expansion conditions are steam curing pressure of 0.5 MPa, steam curing time of 20 minutes, and flash pressure release time of ≤5 seconds. Sodium alginate gels when exposed to water. Steam pretreatment can enhance the stability of the particles. Under optimal conditions, microwave assisted expansion can be used.

[0088] S2: The seaweed residue was inoculated with a composite bacterial agent, with a weight ratio of halophilic bacteria to lactic acid bacteria of 2:1. After anaerobic fermentation for 71 hours, it was carbonized in a tubular furnace to obtain seaweed residue fermentation charcoal. The carbonization conditions were nitrogen shielding gas flow rate of 50 mL / min, heating rate of 10°C / min to 500°C, holding for 2 hours, and then cooling naturally.

[0089] S3: Scallop shell powder (particle size ≤ 0.3 mm) was mixed with 5% citric acid solution at a solid-liquid ratio of 1:3, activated by shaking at 25°C for 2 h, filtered, washed with water until neutral, and dried at 60°C; the activated shell powder was mixed with humic acid chelated magnesium calcium freeze-dried powder (5% w / v) at a weight ratio of 1:5, ultrasonicated at 40 kHz for 30 min, adsorbed by shaking at 25°C for 4 h, dried at 60°C, and then crushed to a particle size ≤ 0.3 mm;

[0090] S4: Mix the products of steps S1-S3 with the remaining binder and extrude them into granular product A2.

[0091] The application of saline-alkali land improver A2 in saline-alkali land improvement is characterized by:

[0092] The soil conditioner is evenly spread on the soil to be improved and mixed with the surface soil at an application rate of 200 kg / mu. This soil conditioner contains no chemical additives and replenishes organic matter after degradation, making it suitable for organic farming areas.

[0093] Example 3

[0094] A volcanic agglomerate rock-seaweed slag composite saline-alkali land improver, characterized by comprising the following components in parts by weight:

[0095] F1: 60 parts of stone powder from the agglomerate rock stripping layer;

[0096] F2: 25 parts of seaweed residue fermented charcoal;

[0097] F3: 10 parts of modified shell powder;

[0098] F4: 5 parts of humic acid-polyvinyl alcohol (weight ratio 1:4) binder.

[0099] A method for preparing a volcanic agglomerate rock-seaweed slag composite saline-alkali land improver, characterized by comprising the following steps:

[0100] S1: Mix tuff rock powder with half of the binder and use screw extrusion to expand to form porous particles. The expansion conditions are: feed section temperature 80°C, compression section temperature 120°C, melting section temperature 150°C, screw speed 220 rpm, die head aperture 5 mm, aspect ratio 3:1, and die head pressure 5 MPa. PVA requires hot melt plasticization, and humic acid is high temperature resistant and suitable for the high temperature section of screw extrusion. It can produce particles with high bonding strength and strong weather resistance.

[0101] S2: Inoculate seaweed residue with a composite bacterial agent, with a weight ratio of halophilic bacteria to lactic acid bacteria of 2:1. After anaerobic fermentation for 72 hours, microwave carbonization is used to obtain seaweed residue fermentation charcoal. The carbonization conditions are microwave power 900W, carbonization time 35 minutes, and rapid cooling after discharge.

[0102] S3: Oyster shell powder (particle size ≤ 0.3 mm) was mixed with 5% citric acid solution at a solid-liquid ratio of 1:3, activated by shaking at 25°C for 2 h, filtered, washed with water until neutral, and dried at 60°C; the activated shell powder was mixed with humic acid chelated magnesium calcium freeze-dried powder (5% w / v) at a weight ratio of 1:5, ultrasonically treated at 40 kHz for 30 min, adsorbed by shaking at 25°C for 4 h, dried at 60°C, and then crushed to a particle size ≤ 0.3 mm;

[0103] S4: The products of steps S1-S3 are mixed with the remaining binder and extruded to form granular product A3.

[0104] The application of saline-alkali land improver A3 in saline-alkali land improvement is characterized by:

[0105] Evenly spread the soil conditioner into the soil to be improved and mix it with the topsoil at a rate of 100 kg / mu. This soil conditioner is highly robust and suitable for mine remediation applications requiring high mechanical strength.

[0106] Comparative Example 1

[0107] The preparation process was essentially the same as in Example 1, except that the mine waste stone powder was not granulated, and 50 parts by weight of mine waste stone powder was used directly in place 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.

[0108] Comparative Example 2

[0109] The preparation process is basically the same as that of Example 1, except that the seaweed residue fermentation charcoal in step S2 is replaced with unfermented and carbonized seaweed residue.

[0110] Comparative Example 3

[0111] The preparation process is basically the same as that of Example 1, except that the modified shell powder is replaced with unactivated and chelated shell powder in step S3. At this time, the saline-alkali soil conditioner D3 is prepared.

[0112] Soil improvement tests were carried out using the products of the above examples and comparative examples to verify their performance.

[0113] 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.

[0114] 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.

[0115] (1) Effects of different soil conditioners on soil pH

[0116] 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).

[0117] Table 1 Effects of different soil amendments on soil pH

[0118]

[0119] After the amendment was applied to the soil, the soil pH changed at different levels.

[0120] (2) Effects of different soil conditioners on soil nutrients

[0121] 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.

[0122] Table 2 Effects of different soil conditioners on soil nutrients

[0123]

[0124] 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.

[0125] (3) Effects of different soil conditioners on soil aeration

[0126] 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.

[0127] Table 3 Effects of different soil conditioners on soil aeration

[0128]

[0129]

[0130] (4) Effect of weathering resistance of different soil conditioners

[0131] 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.

[0132] Table 4 Effect of different soil conditioners on weather resistance

[0133]

[0134] Compared with the blank group, different bonding methods have a significant impact on the weather resistance of the modifier. Polyvinyl alcohol adhesives can improve soil structure in a long-term manner (such as anti-compaction and fertilizer retention), and are suitable for perennial crops or poor soil restoration; sodium carboxymethyl cellulose adhesives are easily decomposed and can be used in mild environments and fast-growing crops; starch-sodium diatomate adhesives are low in cost, have both water retention and air permeability, and are suitable for moderate long-term needs.

[0135] 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 seaweed residue 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.

[0136] 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 pyroclastic rock-seaweed slag composite saline-alkali land improver, characterized in that: It comprises the following components in parts by weight: F1: 40-60 parts of pyroclastic rock powder; F2: 20-30 parts of seaweed residue fermented charcoal; F3: 10-20 parts of modified shell powder; F4: 3 to 5 parts of adhesive.

2. The saline-alkali land improving agent according to claim 1, characterized in that: The pyroclastic rock powder in component F1 has a particle size of ≤0.075 mm and is derived from mud cake produced by wet process, stone powder produced by dry process, and solid waste remaining after mechanical crushing and screening of stripping material or tailings from volcanic rock building stone mines; The seaweed residue fermentation charcoal in component F2 is prepared by anaerobic fermentation of seaweed residue with a composite bacterial agent followed by carbonization; The modified shell powder in component F3 is prepared by acid-activating discarded shells, crushing and drying them, and then loading them with a calcium-magnesium humate complex; the discarded shells are selected from oyster shells or scallop shells; The binder in component F4 is selected from at least one of sodium carboxymethyl cellulose, sodium lignin sulfonate, molasses, bentonite, humic acid, sodium alginate, starch, 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: Pyroclastic rock powder is mixed with a binder and expanded to form porous particles; S2: Inoculating the seaweed residue with a composite bacterial agent, anaerobic fermentation and carbonization to obtain seaweed residue fermentation charcoal; S3: activating the shell powder with citric acid, chelating it with humic acid chelated magnesium calcium freeze-dried powder, drying and crushing it to obtain modified shell 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 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 any one of claims 3 to 5, characterized in that In step S2: The composite bacterial agent is a composite bacterial agent of halophilic bacteria and lactic acid bacteria, and the weight ratio of halophilic bacteria to lactic acid bacteria is (2-3):1; The conditions for the anaerobic fermentation are as follows: inoculating the composite bacterial agent at 5-10% of the dry weight of the seaweed residue, with an initial moisture content of 65-70% and a pH value of 6.5-7.0; after uniform mixing, loading into a sealed fermentation tank, and fermenting in an anaerobic environment for 70-72 hours, maintaining the pressure in the tank at 0.05-0.1 MPa and the temperature at 35-40° C. during the fermentation process.

7. The preparation method according to any one of claims 3 to 5, 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 any one of claims 3 to 5, 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, 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 ≤0.3mm.

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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