Salinized soil Na < + > targeted removal method based on biochar composite material coupling microwave assistance

Abstract

The invention relates to a saline soil Na < + > targeted removal method, in particular to a saline soil Na < + > targeted removal method based on biochar composite material coupling microwave assistance. The invention aims to solve the problems that excessive Na < + > in salinized soil can cause soil aggregate structure collapse, soil hardening and porosity reduction, water and nutrient uptake of plant root systems is severely hindered, and land productivity is sharply declined. The preparation method comprises the following steps: step 1, preparing an amphoteric hydrogel-nano biochar composite material; 2, systematic classification and pretreatment are conducted on the salinized soil; 3, the amphoteric hydrogel-nano biological carbon composite material is put into use according to the grade of the salinized soil; 4, watering is conducted, the soil humidity is maintained to be 20-30%, and the amphoteric hydrogel is promoted to absorb water and expand. The invention belongs to the technical field of soil remediation.

Description

Technical Field

[0001] The present invention relates to a saline soil Na + The invention discloses a targeted removal method, belonging to the technical field of soil remediation. Background Art

[0002] At a time when global ecological and environmental problems are becoming increasingly prominent, saline soil, as a widely distributed soil type that restricts agricultural development and ecological balance, urgently needs effective improvement measures. + It will cause the soil aggregate structure to collapse, the soil to become compacted, and the porosity to decrease, which will seriously hinder the plant roots' absorption of water and nutrients, leading to a sharp decline in land productivity.

[0003] Existing methods for saline soil remediation primarily focus on leaching, phytoremediation, and organic soil remediation agents (such as green fertilizers and biochar). Compared to these other methods, organic soil remediation agents offer multi-dimensional remediation benefits, including reducing ion concentrations, increasing soil fertility, and enhancing microbial activity.

[0004] As an emerging soil conditioner, biochar has shown potential in improving soil physical structure, absorbing soil salt, and activating microbial activity due to its unique porous structure and rich and diverse functional groups. However, the following problems still exist: on the one hand, although reducing the biochar particle size to nanometer level will significantly increase its ion adsorption sites, Na + The adsorption capacity is enhanced, but nano-sized particles are easily transferred to groundwater, threatening the health of water ecology. On the other hand, the solid-solid mass transfer rate between traditional biochar and soil particles is slow, and the cation exchange adsorption capacity is weak, which greatly limits its adsorption of Na + The adsorption efficiency is low, and the salt ions after adsorption are easily released for a second time, resulting in frequent soil salt return, making it difficult to maintain the improvement effect for a long time.

[0005] As a three-dimensional network material constructed by hydrophilic polymer chains, hydrogel is well-known for its good water absorption and water retention. It can effectively regulate water distribution in the soil environment and has a certain auxiliary effect on improving soil structure. However, when hydrogel is used alone to treat saline soil, its cation absorption, especially Na + The adsorption capacity of saline soil is seriously insufficient and cannot fundamentally break the Na + problem.

[0006] Microwave technology, as an emerging auxiliary tool, can reduce the binding energy between soil particles and Na⁺ through dielectric heating, promoting ion desorption; enhance microconvection of soil pore water through transient thermal effects, accelerating ion migration; and alter the surface potential of soil particles through non-thermal effects, lowering the energy barrier for ion detachment. Therefore, coupling microwave technology with amphoteric hydrogel-nanobiochar composites can overcome the mass transfer limitations of traditional remediation technologies and improve desalination efficiency. Summary of the Invention

[0007] The present invention is to solve the problem of excessive Na + It will cause the collapse of soil aggregate structure, soil compaction, reduced porosity, and seriously hinder the uptake of water and nutrients by plant roots, leading to a sharp decline in land productivity. Therefore, a method of Na-based saline soil treatment based on biocarbon composite material coupled with microwave assisted + Targeted removal methods.

[0008] The technical solution adopted by the present invention to solve the above problems is: the steps of the present invention include: Step 1, preparing an amphoteric hydrogel-nanobiocarbon composite material; Step 2: Systematically classify and pre-treat the saline soil; Step 3: Implementing the use of the amphoteric hydrogel-nano-biocarbon composite material according to the grade of saline soil; Step 4: Water and maintain the soil moisture at 20-30% to promote the water absorption and expansion of the amphoteric hydrogel.

[0009] Furthermore, the step of preparing the amphoteric hydrogel-nanobiocarbon composite material in step 1 includes: Step 101: Select biomass raw materials with a wide range of sources and rich carbon content, and perform high-temperature oxygen-free pyrolysis at a temperature of 500-700°C. The pyrolysis products are then activated to deeply optimize the pore structure and functional group layout so that the specific surface area of ​​the biochar reaches 300-500 , the pore size distribution is strictly controlled within 2 to 50 nm, limiting the biochar particle size to the nanoscale of 20 to 50 nm; Step 102: Select a hydrophilic polymer to build a skeleton, and incorporate a zwitterionic monomer with polyelectrolyte resistance for modification; Step 103: Simultaneously add monomers with acidic functional groups to enhance the electrostatic capture efficiency of cations; the cross-linking agent is selected to be biodegradable; Step 104: adjusting the mass ratio of the polymer, the zwitterionic monomer, and the cross-linking agent within a range of 3:1 to 5:1; Step 105: evenly disperse the nano-biochar in the solvent, and perform ultrasonic treatment at an ultrasonic power of 300-500W for 30-60 minutes, in combination with mechanical stirring at a stirring speed of 200-300 rpm for 60-120 minutes. Step 106: dissolving the hydrophilic polymer, zwitterionic monomer, and crosslinking agent into the dispersion solution one by one, stirring at a constant speed of 150-200 rpm for 30-60 minutes at a temperature-controlled environment of 40-50° C. to allow the components to be fully and evenly blended to form a pre-gel solution; Step 107: Add an initiator to the pregel solution, raise the temperature to 60-70°C, and continue the reaction for 2-3 hours while passing nitrogen gas to drive the polymer cross-linking polymerization reaction to proceed, thereby encapsulating the nano-biochar in the three-dimensional network structure of the amphoteric hydrogel, and finally successfully obtaining an amphoteric hydrogel-nano-biochar composite material.

[0010] Furthermore, the activation methods of the pyrolysis products include physical activation and chemical activation. The physical activation is the carbon dioxide method, in which the pressure of the introduced carbon dioxide is 0.8 MPa and the duration is 1.5 h; the chemical activation is the phosphoric acid method, in which the impregnation concentration of phosphoric acid is 15% and the duration is 2 h.

[0011] Furthermore, step 2 specifically includes: Collect saline soil samples and subdivide the saline soil into light EC = 2-4 dS / m, moderate EC = 4-8 dS / m, and heavy EC = 8-16 dS / m. Place the collected soil samples in a naturally ventilated environment to air dry, and after air drying, sieve to remove impurities.

[0012] Furthermore, step 3 specifically includes: Step 301: For lightly saline soil, the composite material is uniformly added at a mass ratio of 1 to 3% of the soil mass; for moderately saline soil, the addition ratio is 3 to 5%; for heavily saline soil, the addition ratio is 5 to 8%; Step 302: Use mechanical mixing equipment or manual fine tillage to fully mix the composite material with the saline soil to ensure that the material and the soil are evenly mixed; Step 303: Use a microwave device with a frequency of 2450 MHz to irradiate the mixed soil: for slightly saline soil, set the power to 300-500 W and the irradiation time to 5-10 minutes; for moderately saline soil, set the power to 500-800 W and the irradiation time to 10-15 minutes; for heavily saline soil, set the power to 800-1200 W and the irradiation time to 15-20 minutes.

[0013] Furthermore, in step 3, the light addition ratio is 2%, the moderate addition ratio is 4%, and the heavy addition ratio is 6%.

[0014] Furthermore, in step 3, the power for slightly saline soil is 400 W, and the time is 8 minutes; the power for moderately saline soil is 600 W, and the time is 12 minutes; and the power for heavily saline soil is 1000 W, and the time is 18 minutes.

[0015] Furthermore, the suitable humidity range is 25%.

[0016] The beneficial effects of the present invention are: 1. This invention, with its innovative combination of amphoteric hydrogel and nano-biochar composite material and accompanying precise improvement process, demonstrates significant advantages in all aspects of saline soil treatment. 2. In terms of material preparation and performance optimization, this invention uses high-temperature pyrolysis of biomass raw materials combined with physical / chemical activation techniques to produce nano-biochar with a high specific surface area and a multi-level pore structure. This not only retains a high adsorption capacity but also effectively suppresses the risk of nanoparticle migration through hydrogel encapsulation. The amphoteric hydrogel, by introducing anti-polyelectrolyte monomers and acidic functional groups, achieves intelligent regulation of water channel expansion in high-salt environments (promoting ion migration) and channel closure in low-salt environments (inhibiting secondary release). 3. The microwave thermal effect increases soil temperature, reduces the binding energy between Na⁺ and soil particles, and stimulates pore water micro-convection, significantly improving mass transfer efficiency and greatly shortening the desalination cycle. In addition, nano-biochar provides abundant adsorption sites, and the amphoteric hydrogel synergistically adsorbs through electrostatic interaction and hydrogen bond network, significantly improving the Na⁺ removal rate and reducing electrical conductivity. 4. In the practice of saline soil improvement, the present invention implements policies based on the precise classification of soil salinization levels, ensuring that the amount of composite material added matches the soil requirements, avoiding resource waste and insufficient improvement. Simultaneously, a high-precision conductivity meter is used to monitor changes in soil conductivity in real time. After improvement, the present invention reduces soil conductivity, effectively improving soil salinization and creating a relatively low-salt environment for plant growth. 5. The improved soil aggregate structure is significantly optimized, the porosity is significantly increased, and the soil organic matter content is significantly improved. The nanobiochar itself is rich in high-quality organic matter such as carbon elements, and the amphoteric hydrogel-nanobiochar composite material creates a suitable habitat for soil microorganisms, promotes microbial activity, accelerates the decomposition and transformation of soil organic matter, improves soil fertility, and forms a virtuous cycle of soil improvement. The present invention uses environmentally friendly materials and processes throughout the process, avoiding the problems of soil compaction, microbial community destruction and secondary pollution caused by chemical modifiers, effectively ensuring the health and stability of the soil ecosystem, and providing a highly innovative and feasible example for sustainable agriculture and ecological restoration. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a flow chart of the present invention. DETAILED DESCRIPTION

[0018] Specific embodiment 1: Based on biocarbon composite material coupled with microwave assisted saline soil Na + Targeted removal method, the specific steps include: Step 1: Prepare amphoteric hydrogel-nanobiochar composite materials. Select biomass raw materials with a wide range of sources and rich carbon content, such as discarded fruit tree branches and rice and wheat straw, and subject them to high-temperature anaerobic pyrolysis (pyrolysis temperature 500-700°C). The pyrolysis products are then physically activated (for example, by introducing carbon dioxide or water vapor and treating at 0.5-1.0 MPa for 1-2 hours, or chemically activated (impregnation in 10-20% phosphoric acid followed by thorough washing and drying) to deeply optimize the pore structure and functional group layout, so that the biochar specific surface area accurately reaches 300-500 The pore size distribution is strictly controlled within the range of 2-50 nm, and the biochar particle size is finely limited to the nanoscale (20-50 nm), thereby ensuring high ion adsorption potential while minimizing the risk of nanoparticle migration. At the same time, highly hydrophilic polymers such as polyacrylamide and polyvinyl alcohol are selected to build the skeleton, and zwitterionic monomers with unique anti-polyelectrolyte capabilities are incorporated for modification. Such zwitterionic monomers can responsively regulate the adaptability of water transport channels in high-salt environments, and can promote channel closure in low-salt environments, effectively preventing the adsorbed Na + The secondary desorption process is carried out by adding appropriate amounts of monomers carrying acidic functional groups such as carboxyl and sulfonic acid groups to enhance the electrostatic capture of cations. A biodegradable crosslinker is selected to ensure the material's comprehensive eco-friendliness. The mass ratio of polymer, zwitterionic monomer, and crosslinker is adjusted between 3:1 and 5:1. Finally, the nano-biochar is evenly dispersed in the solvent and subjected to ultrasonic treatment (300-500 W for 30-60 minutes) and mechanical stirring (200-300 rpm for 60-120 minutes) to prevent biochar agglomeration. The hydrophilic polymer, zwitterionic monomer, and crosslinker are then dissolved in the dispersion in appropriate proportions. Under a controlled temperature of 40-50°C, the mixture is stirred at a constant speed of 150-200 rpm for 30-60 minutes to ensure thorough and uniform mixing of the components, thereby forming a pre-gel solution. Subsequently, an initiator (ammonium persulfate, azobisisobutyronitrile, etc., with an amount of 0.5-1.5% of the total mass of the reactants) is added to the pre-gel solution, the temperature is raised to 60-70°C, and nitrogen is passed through to continue the reaction for 2-3 hours to drive the polymer cross-linking polymerization reaction, encapsulating the nanobiochar in the three-dimensional network structure of the amphoteric hydrogel, and finally successfully obtaining an amphoteric hydrogel-nanobiochar composite material.

[0019] Step 2: Systematically classify and pre-treat saline soil. Collect saline soil samples from various regions and with diverse origins. These samples are categorized as mild (EC = 2-4 dS / m), moderate (EC = 4-8 dS / m), and severe (EC = 8-16 dS / m). Air-dry the collected soil samples in a naturally ventilated environment. After drying, they are sieved to remove debris, rocks, and other impurities.

[0020] Step 3: Targeted application of the amphoteric hydrogel-nanobiochar composite material is performed based on the saline soil grade. For mildly saline soil, the composite material is evenly added at a mass ratio of 1-3% of the soil mass. For moderately saline soil, the addition ratio is moderately increased to 3-5%, and for severely saline soil, the addition ratio is further increased to 5-8%. The composite material and saline soil are thoroughly mixed using mechanical mixing equipment or manual tillage to ensure uniform mixing and maximize the material's improvement potential. Simultaneously, the mixed soil is irradiated using a 2450 MHz microwave device: for mildly saline soil, the power setting is 300-500 W for 5-10 minutes; for moderately saline soil, the power setting is 500-800 W for 10-15 minutes; and for severely saline soil, the power setting is 800-1200 W for 15-20 minutes.

[0021] Step 4: Water appropriately to maintain soil moisture at 20-30% to promote sufficient water absorption and expansion of the amphoteric hydrogel. At the same time, select salt-tolerant plant varieties such as Suaeda salsa, Suaeda salsa, and Lycium barbarum based on local climate and soil conditions, and implement a dense planting plan according to the plant's own growth habits. During the growth and development of the plant's root system, on the one hand, root secretions continuously improve the soil microenvironment, promote the interaction between the amphoteric hydrogel-nanobiochar composite material and the soil, and accelerate the soil improvement process; on the other hand, the plant's ability to absorb nutrients from the soil is utilized to reduce soil salt concentration, achieving the goal of a virtuous ecological cycle that synergizes with the composite material to improve saline soil.

[0022] Preferably, when preparing the composite material in step 1, if the physical activation carbon dioxide method is used for the activation treatment of biochar, the pressure of the introduced carbon dioxide is 0.8 MPa and the duration is 1.5 h; if the chemical activation phosphoric acid method is used, the impregnation concentration of phosphoric acid is 15% and the duration is 2 h.

[0023] Preferably, in step 3, the light addition ratio is 2%, the moderate addition ratio is 4%, and the heavy addition ratio is 6%.

[0024] Preferably, in step 3, the power for slightly saline soil is 400 W, and the time is 8 minutes; the power for moderately saline soil is 600 W, and the time is 12 minutes; and the power for heavily saline soil is 1000 W, and the time is 18 minutes.

[0025] Preferably, in step 4, the suitable humidity range is 25%.

[0026] Example Example 1 (1) A saline soil sample was collected from a coastal saline soil area. The soil conductivity was 6 dS / m and the sodium ion content was about 4500 mg / kg, which is classified as moderate saline soil. Abandoned fruit tree branches were selected for high-temperature anaerobic pyrolysis. The pyrolysis temperature was controlled at 550℃ for 3 hours. After pyrolysis, the physical activation of carbon dioxide was used. The carbon dioxide pressure was 0.6 MPa for 1.5 hours to prepare nano-biochar with a specific surface area of ​​350 , the pore size distribution is 10-40 nm, and the particle size is 30-40 nm. Polyacrylamide was selected as the hydrophilic polymer, and zwitterionic monomers with anti-polyelectrolyte ability and appropriate carboxyl monomers were introduced. The cross-linking agent was selected to be biodegradable, and the mixture was prepared in a mass ratio of 4:1:0.5. Ultrasonic treatment (power 400W) was performed for 45 minutes, and mechanical stirring (stirring speed 250 rpm, stirring for 90 minutes) was used to prepare a stable dispersion. For the moderately saline soil collected, the composite material was added at 4% of the soil mass, and the composite material and the soil were fully mixed with the help of a tillage machine. After mixing, microwave irradiation was performed at 600 W for 12 minutes, and then the soil moisture was maintained at 22% by watering in moderation. Salicornia salsa seedlings were planted and observed regularly. Two months later, it was observed that the Salicornia salsa seedlings were growing well, with an average plant height of 12 cm higher than that of the control group, and the root system was more developed. Soil testing showed that Na + The removal rate reached 75%, the electrical conductivity decreased by 40%, the soil aggregate structure was significantly improved, and the porosity increased, which preliminarily verified the improvement effect of this program on moderately saline soil and its role in promoting plant growth.

[0027] Example 2 (1) Severe saline soil samples were collected from an inland soda saline soil area. The soil conductivity was as high as 12 dS / m and the sodium ion content was about 8500 mg / kg. Rice and wheat straw were used as raw materials for high-temperature anaerobic pyrolysis at 650℃ for 3 h. Then, chemical activation phosphoric acid method was used with phosphoric acid impregnation concentration of 18% for 2 h. Nano-biochar with a specific surface area of ​​450 , pore size distribution 20 - 50 nm, particle size 20 - 30 nm. The hydrophilic polymer is polyvinyl alcohol, matched with zwitterionic monomers and sulfonic acid group-containing monomers, and a biodegradable cross-linking agent. It is formulated at a mass ratio of 5:1:0.8 and mixed evenly by ultrasound (power 450W, duration 50 min) and mechanical stirring (speed 280 rpm, time 100 min). For this heavily saline soil, the composite material is added at 7% of the soil mass, and the soil and materials are mixed evenly through manual fine plowing. After mixing, microwave irradiation of 1000 W is carried out for 18 minutes, and appropriate amount of water is applied to maintain the soil moisture at 25%. Lycium barbarum seedlings are planted and observed regularly. Three months later, the survival rate of Lycium barbarum seedlings reached 75%, and the soil Na + The removal rate reached 80%, the electrical conductivity decreased by 45%, the organic matter content increased, and the soil structure was optimized, proving that this program is effective in improving heavily saline soil.

[0028] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention has been disclosed as a preferred embodiment as above, it is not intended to limit the present invention. Any technician familiar with the present profession can make some changes or modifications to equivalent embodiments of equivalent changes using the technical content disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent replacement and improvement of the above embodiments made according to the technical essence of the present invention, within the spirit and principles of the present invention, without departing from the content of the technical solution of the present invention, shall still fall within the scope of protection of the technical solution of the present invention.

Claims

1. Biochar composite coupled with microwave-assisted saline soil Na + The targeted removal method is characterized in that The specific steps include: Step 1, preparing an amphoteric hydrogel-nanobiocarbon composite material; Step 2: Systematically classify and pre-treat the saline soil; Step 3: Implementing the use of the amphoteric hydrogel-nano-biocarbon composite material according to the grade of saline soil; Step 4: Water and maintain the soil moisture at 20-30% to promote the water absorption and expansion of the amphoteric hydrogel.

2. The biocarbon composite material coupled with microwave-assisted saline soil Na according to claim 1 + The targeted removal method is characterized in that The steps of preparing the amphoteric hydrogel-nano-biocarbon composite material in step 1 include: Step 101: Select biomass raw materials with a wide range of sources and rich carbon content, and subject them to high-temperature oxygen-free pyrolysis at a temperature of 500-700°C. The pyrolysis products are then activated to deeply optimize the pore structure and functional group layout so that the specific surface area of ​​the biochar reaches 300-500m 2 / g, the pore size distribution is strictly controlled within 2 to 50 nm, and the biochar particle size is limited to the nanoscale of 20 to 50 nm; Step 102: Select a hydrophilic polymer to build a skeleton, and incorporate a zwitterionic monomer with polyelectrolyte resistance for modification; Step 103: Simultaneously add monomers with acidic functional groups to enhance the electrostatic capture efficiency of cations; the cross-linking agent is selected to be biodegradable; Step 104: adjusting the mass ratio of the polymer, the zwitterionic monomer, and the cross-linking agent within a range of 3:1 to 5:1; Step 105: evenly disperse the nano-biochar in the solvent, and perform ultrasonic treatment at an ultrasonic power of 300-500 W for 30-60 min, in combination with mechanical stirring at a stirring speed of 200-300 rpm for 60-120 min; Step 106: dissolving the hydrophilic polymer, zwitterionic monomer, and crosslinking agent into the dispersion solution one by one, stirring at a constant speed of 150-200 rpm for 30-60 minutes under a temperature-controlled environment of 40-50° C. to allow the components to be fully and evenly blended to form a pre-gel solution; Step 107: Add an initiator to the pregel solution, raise the temperature to 60-70°C, and continue the reaction for 2-3 hours while passing nitrogen to drive the polymer cross-linking polymerization reaction to proceed, thereby encapsulating the nano-biochar in the three-dimensional network structure of the amphoteric hydrogel, and finally successfully obtaining an amphoteric hydrogel-nano-biochar composite material.

3. The biocarbon composite material coupled with microwave-assisted saline soil Na according to claim 2 + The targeted removal method is characterized in that The activation methods of pyrolysis products include physical activation and chemical activation. The physical activation is the carbon dioxide method, in which the pressure of the carbon dioxide introduced is 0.8 MPa and the duration is 1.5 hours; the chemical activation is the phosphoric acid method, in which the impregnation concentration of phosphoric acid is 15% and the duration is 2 hours.

4. The biocarbon composite material coupled with microwave-assisted saline soil Na according to claim 1 + The targeted removal method is characterized in that Step 2 specifically includes: Collect saline soil samples and subdivide the saline soil into mild EC = 2-4dS / m, moderate EC = 4-8dS / m, and severe EC = 8-16dS / m. Place the collected soil samples in a naturally ventilated environment to air dry, and after air drying, sieve to remove impurities.

5. The biocarbon composite material coupled with microwave-assisted saline soil Na + The targeted removal method is characterized in that Step 3 specifically includes: Step 301: For slightly saline soil, the composite material is uniformly added at a mass ratio of 1 to 3% of the soil mass; for moderately saline soil, the addition ratio is 3 to 5%; and for heavily saline soil, the addition ratio is 5 to 8%. Step 302: Use mechanical mixing equipment or manual fine tillage to fully mix the composite material with the saline soil to ensure that the material and the soil are evenly mixed; Step 303: Use microwave equipment with a frequency of 2450 MHz to irradiate the mixed soil: for slightly saline soil, set the power to 300-500 W and the irradiation time to 5-10 minutes; for moderately saline soil, set the power to 500-800 W and the irradiation time to 10-15 minutes; for heavily saline soil, set the power to 800-1200 W and the irradiation time to 15-20 minutes.

6. The biocarbon composite material coupled with microwave-assisted saline soil Na according to claim 5 + The targeted removal method is characterized in that In step 3, the light addition ratio is 2%, the moderate addition ratio is 4%, and the heavy addition ratio is 6%.

7. The biocarbon composite material coupled with microwave-assisted saline soil Na + The targeted removal method is characterized in that In step 3, the power for slightly saline soil is 400W, and the time is 8 minutes; the power for moderately saline soil is 600W, and the time is 12 minutes; the power for heavily saline soil is 1000W, and the time is 18 minutes.

8. The biocarbon composite material coupled with microwave-assisted saline soil Na + The targeted removal method is characterized in that The suitable humidity range is 25%.

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