Multifunctional composite soil conditioner and preparation method thereof

Abstract

The invention belongs to the technical field of soil remediation, and particularly relates to a multifunctional composite soil conditioner and a preparation method thereof. The composition comprises a component A and a component B, the component A is prepared from the following components in parts by weight: 35 to 50 parts of modified charcoal, 8 to 12 parts of diatomite, 3 to 5 parts of bentonite, 13 to 18 parts of chitosan modified humic acid and 4 to 6 parts of nano silicon dioxide; the component B is prepared from the following components: 8 to 12 parts of lime powder, 5 to 10 parts of polyvinyl alcohol, 5 to 10 parts of polylactic acid, 5 to 8 parts of nanocrystalline cellulose, 6 to 10 parts of plant extract and 5 to 8 parts of sodium alginate. According to the invention, a stable three-dimensional adsorption network is constructed by using biochar and a nano material, so that the heavy metal fixing capability is enhanced; the chitosan modified humic acid promotes the growth of beneficial microorganisms and improves the self-repairing capability of the soil; slow-release lime powder ensures stable adjustment of the pH value, and polyvinyl alcohol and the like form a protective layer to ensure a long-acting effect.

Description

Technical Field

[0001] The invention belongs to the technical field of soil remediation, and specifically relates to a multifunctional composite soil conditioner and a preparation method thereof. Background Art

[0002] With the growth of the global population and the acceleration of urbanization, land resources have become increasingly precious. At the same time, agricultural production and industrial activities have also had a serious impact on soil quality. Soil degradation, acidification, salinization and pollution are becoming increasingly prominent. These problems not only affect the yield and quality of crops, but also threaten the stability and sustainability of the ecosystem. In order to meet these challenges, scientists are committed to developing new multifunctional composite soil conditioners to improve soil structure, regulate soil pH, enhance soil water and fertilizer retention capacity, promote healthy plant growth, and effectively treat polluted or degraded soils. At present, soils in many regions are facing many problems such as acidification, compaction, and nutrient imbalance. For example, in some areas in southern China, due to the long-term and large-scale use of chemical fertilizers, the soil pH has dropped and obvious acidification has occurred; in the arid and semi-arid areas in the north, there are serious wind and water erosion problems, and secondary salinization caused by improper irrigation has further aggravated the deterioration of soil quality. In addition, with the development of industrialization, heavy metal pollution has also become a problem that cannot be ignored. Therefore, there is an urgent need for a comprehensive solution that can solve the above-mentioned soil problems and increase crop yields - that is, a multifunctional composite soil conditioner.

[0003] The goal of multifunctional composite soil conditioners is usually to improve the physical, chemical and biological properties of the soil to promote plant growth and reduce the impact of pollutants. The functions of soil conditioners include improving soil structure, increasing nutrient supply, enhancing microbial activity, etc. For example, organic soil conditioners (such as compost, humus, etc.) improve soil structure and increase nutrient supply by increasing the organic matter content of the soil; while inorganic soil conditioners (such as lime, phosphate, etc.) can adjust the pH value of the soil and improve soil nutrients. For heavy metal pollution, heavy metal adsorbents (such as activated carbon, bentonite and biochar, etc.) can effectively adsorb and fix heavy metals in the soil and reduce the absorption of these pollutants by plants. In addition, phytoremediation and chemical remediation are also effective treatment methods that can remove pollutants in the soil by changing the form of heavy metals or using specific plants. Therefore, based on the above problems, it is extremely necessary to develop a multifunctional composite soil conditioner that simultaneously inhibits soil acidification and heavy metal pollution. Summary of the invention

[0004] In view of the defects of the prior art, the object of the present invention is to provide a multifunctional composite soil conditioner and a preparation method thereof.

[0005] The technical effect of the present invention is achieved by the following technical scheme: a multifunctional composite soil conditioner, which comprises component A and component B; the component A comprises the following components: 35 to 50 parts of modified biochar, 8 to 12 parts of diatomaceous earth, 3 to 5 parts of bentonite, 13 to 18 parts of chitosan modified humic acid and 4 to 6 parts of nano silicon dioxide; the component B comprises the following components: 8 to 12 parts of lime powder, 5 to 10 parts of polyvinyl alcohol, 5 to 10 parts of polylactic acid, 5 to 8 parts of nanocrystalline cellulose, 6 to 10 parts of plant extracts and 5 to 8 parts of sodium alginate.

[0006] Preferably, the plant extract is prepared by extracting active ingredients from 0.6-1 parts of garlic, 0.5-0.9 parts of wormwood, 0.5-0.9 parts of mint, 0.6-1 parts of prickly ash, 0.5-0.9 parts of chili, 0.5-0.9 parts of perilla, 0.6-1 parts of tobacco, 0.8-1 parts of onion, 0.4-0.6 parts of star anise, 0.4-0.8 parts of neem leaves and 0.6-1 parts of bidens pilosa by conventional technical means and mixing them.

[0007] Preferably, the specific preparation steps of the modified biochar are as follows: A1: Add ferrous sulfate to deionized water, stir and mix evenly, adjust the pH to neutral with NaOH solution, and let it react at room temperature for 30 to 60 minutes to obtain a precursor iron solution; A2: Select corn stalks, crush, wash, dry at 60-100°C for 12-24 hours, place in nitrogen environment after drying, heat at 600-800°C for 3-6 hours, cool naturally to room temperature, wash with deionized water, and dry at 60°C for 24 hours to obtain biochar; A3: Slowly add the precursor iron solution prepared in step A2 to the biochar prepared in step A1, slowly add sodium borohydride, stir and disperse evenly under nitrogen environment, let stand for 6 to 12 hours, centrifuge, filter, and dry at 50 to 60° C. for 12 hours to obtain modified biochar; Preferably, in step A1, the ratio of the amount of ferrous sulfate to deionized water is 1 g:100 mL:0.2-0.3 g; Preferably, in step A3, the ratio of the amount of the precursor iron solution, biochar and sodium borohydride is 6-10 mL: 1 g: 0.2-0.3 g.

[0008] Preferably, the specific preparation steps of the chitosan-modified humic acid are as follows: B1: Dissolve chitosan in 1wt% acetic acid solution, stir and mix evenly to obtain a chitosan solution; add humic acid into deionized water, heat to 60°C in a water bath, stir and dissolve evenly to obtain a 10-20wt% humic acid solution; B2: slowly adding the humic acid solution prepared in step B1 to the chitosan solution prepared in step B1, then adding glutaraldehyde, controlling the temperature at 30-40° C., stirring the reaction for 1-2 hours, centrifuging, filtering, and vacuum drying at 60° C. for 12-24 hours to obtain chitosan-modified humic acid; Preferably, in step B1, the ratio of the amount of chitosan to the amount of acetic acid solution is 1-2 g:100 mL; Preferably, in step B2, the volume ratio of the humic acid solution to the chitosan solution is 1:1-2; and the amount of glutaraldehyde is 5% of the total mass of the humic acid and chitosan substrates.

[0009] Preferably, another aspect of the present invention is to provide a method for preparing a multifunctional composite soil conditioner, and the specific preparation steps are as follows: S1: adding polyvinyl alcohol to 10 to 20 parts by weight of deionized water, stirring and dissolving uniformly to obtain a polyvinyl alcohol solution; adding polylactic acid to 20 to 30 parts by weight of dichloromethane, stirring and dissolving uniformly to obtain a polylactic acid solution; S2: adding lime powder to the polyvinyl alcohol solution prepared in step S1, stirring and dispersing it evenly, and then slowly adding it to the polylactic acid solution, controlling the pH to be neutral, stirring at 500-800 rpm for 2-3 hours, standing for 6-12 hours, centrifuging, filtering, and freeze-drying at -40°C for 24 hours to obtain coated lime powder; S3: adding nanocrystalline cellulose to 10 to 20 times the weight of deionized water, and dispersing it evenly by ultrasonic treatment to obtain a nanocrystalline cellulose dispersion; adding the nanocrystalline cellulose dispersion to nano-silicon dioxide, and dispersing it evenly by ultrasonic treatment, standing for 2 to 4 hours, and freeze-drying at -40°C for 24 hours to obtain a composite powder; S4: adding sodium alginate to 50 times the weight of deionized water, stirring and dissolving uniformly to obtain a sodium alginate solution; spraying the sodium alginate uniformly onto the coated lime powder prepared in step S2, stirring at 500 rpm for 30 minutes, and spray drying to obtain slow-release lime particles; S5: uniformly mixing the modified biochar, diatomaceous earth, chitosan-modified humic acid, plant extract, the composite powder prepared in step S3, and the slow-release lime particles prepared in step S4 using a ball mill, and vacuum drying at 40° C. for 12 h to obtain a composite soil conditioner; Preferably, in step S4, the spray drying parameters are: inlet temperature 150-160° C., outlet temperature 80-90° C., and atomization pressure 3-5 bar.

[0010] The beneficial effects of the present invention are as follows: The present invention has developed a multifunctional composite soil conditioner including component A and component B, wherein component A mainly targets heavy metal pollution in the soil, and reduces the bioavailability of pollutants through efficient fixation and conversion; component B focuses on regulating the pH of the soil and improving the physical structure, providing a suitable growth environment and nutrient retention; the combination of the two can not only effectively control pollution, but also optimize the soil environment and promote the healthy growth of plants. Biochar is modified with nano zero-valent iron, and based on the excellent reducibility of nano zero-valent iron (nZVI), heavy metal ions (such as lead, cadmium, mercury, etc.) are effectively reduced to a more stable form; combined with a large number of adsorption sites provided by the porous structure of biochar, the fixation capacity of heavy metals is significantly improved. In addition, biochar has a highly porous and hydrophobic surface structure, which provides a physical barrier for nano zero-valent iron, reduces the contact of oxygen and water, and effectively delays the oxidative inactivation of nano zero-valent iron. At the same time, the porous structure of biochar helps to evenly disperse nano zero-valent iron, prevent its agglomeration, and further improve its stability. Nano-silicon dioxide is not only suitable for harsh conditions due to its own chemical stability and mechanical strength, but its small size and high dispersibility enable it to be effectively and evenly distributed in the porous structure of biochar and to build a mesh structure with nanocrystalline cellulose, together building a highly effective three-dimensional adsorption network, providing a more stable environment and extending the active life of nano zero-valent iron. Chitosan-modified humic acid enhances the fixation ability of heavy metals through its powerful chelation effect. At the same time, humic acid can improve the dispersibility and solubility of chitosan, making it more evenly distributed in the soil and enhancing its contact with harmful microorganisms. At the same time, humic acid itself has the ability to promote the growth of beneficial microorganisms, forming a dual effect of beneficial microorganisms and antibacterial chitosan, inhibiting harmful microorganisms while promoting the healthy development of soil microbial communities. Through the joint action of multiple materials, not only can the multi-level fixation of heavy metals be achieved through physical adsorption and chemical reaction, but also the reproduction of beneficial microorganisms can be promoted by providing organic matter and carbon sources, thereby enhancing the biological activity and self-repairing ability of the soil. Lime powder and plant extracts (such as onions and neem leaves contain organic acids) can neutralize soil acidity and raise the soil pH to an appropriate range. Polyvinyl alcohol and polylactic acid, as biodegradable polymers, coat lime powder to form a slow-release structure to ensure the continuous release of lime, avoid drastic fluctuations in pH, and provide a long-term and stable acid-base adjustment effect. Sodium alginate, as a binder, enhances the stability of slow-release lime particles and ensures their uniform distribution and slow release in the soil; nanocrystalline cellulose not only enhances the soil's aggregate structure and mechanical strength, but also prevents soil compaction. Plant extracts such as wormwood, perilla and onion contain organic matter, which can serve as a nutrient source for beneficial microorganisms, promote the reproduction of beneficial bacteria, and enhance soil biological activity. The slow-release and stable release mechanism constructed by a variety of materials provides long-lasting pH adjustment and nutrient supply, ensuring that crops receive continuous nutrient support throughout the growth cycle, while optimizing the physical structure of the soil and improving air permeability, drainage and water retention.

[0011] In summary, the composite soil conditioner constructed by the synergistic effect of materials in the present invention can not only stably adjust the soil pH value and ensure the suitability of the soil environment, but also efficiently fix heavy metal pollution through multiple adsorption mechanisms, significantly reduce its biological effectiveness, and protect the health of crops and ecosystems. At the same time, biochar, diatomaceous earth and nanocrystalline cellulose jointly optimize the physical structure of the soil, improve air permeability, drainage and pellet stability. Nutrients are effectively managed through the adsorption retention of biochar and diatomaceous earth and the sustained release mechanism of slow-release lime-based materials, ensuring that crops obtain the required nutrients in a long-term and balanced manner, and improving crop yield and quality. Chitosan-modified humic acid promotes the reproduction of beneficial microorganisms by providing organic matter and carbon sources, enhances the biological activity and self-repairing ability of the soil, and further improves soil health and productivity. In addition, polyvinyl alcohol and polylactic acid polymer networks and sodium alginate ensure the mechanical stability and ease of application of the conditioner, and ensure the uniform distribution and long-term stability of each functional component in the soil. All materials are selected from environmentally friendly and degradable ingredients to ensure the sustainability and environmental friendliness of the conditioner, which meets the needs of green agricultural development. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings in the following description are only for the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0013] Figure 1 It is a graph showing the adsorption results of metal arsenic by the composite soil conditioner prepared in Example 2 of the present invention and Comparative Examples 1 to 5; Figure 2 It is a graph showing the adsorption results of metal cadmium by the composite soil conditioner prepared in Example 2 of the present invention and Comparative Examples 1 to 5; Figure 3 It is a graph showing the adsorption results of metal lead by the composite soil conditioner prepared in Example 2 of the present invention and Comparative Examples 1 to 5; Figure 4 It is a graph showing the test results of acidified soil of the composite soil conditioner prepared in Example 2 of the present invention and Comparative Examples 1 to 5; Figure 5 This is a SEM scanning electron microscope image of the composite soil conditioner prepared in Example 2 of the present invention. DETAILED DESCRIPTION

[0014] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them; based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention. It should be noted that, unless otherwise specified, the raw materials involved in the present invention are purchased through conventional commercial channels.

[0015] Embodiment 1: A multifunctional composite soil conditioner, comprising component A and component B; the component A comprises the following components: 35 parts of modified biochar, 8 parts of diatomaceous earth, 3 parts of bentonite, 13 parts of chitosan-modified humic acid and 4 parts of nano-silicon dioxide; the component B comprises the following components: 8 parts of lime powder, 5 parts of polyvinyl alcohol, 5 parts of polylactic acid, 5 parts of nanocrystalline cellulose, 6 parts of plant extracts and 5 parts of sodium alginate.

[0016] The specific preparation steps of modified biochar are as follows: A1: Add 5 g of ferrous sulfate to 500 mL of deionized water, stir and mix well, adjust the pH to neutral with NaOH solution, and let it react at room temperature for 30 min to obtain a precursor iron solution; A2: Select corn stalks, crush, wash, and dry at 60°C for 24 hours. After drying, place them in a nitrogen environment, heat them at 600°C for 6 hours, cool them naturally to room temperature, wash them with deionized water, and dry them at 60°C for 24 hours to obtain biochar; A3: Slowly add 300 mL of the precursor iron solution prepared in step A2 to 5 g of the biochar prepared in step A1, slowly add 1 g of sodium borohydride, stir and disperse evenly under nitrogen environment, let stand for 6 hours, centrifuge, filter, and dry at 50°C for 12 hours to obtain modified biochar; The specific preparation steps of chitosan modified humic acid are as follows: B1: Dissolve 10g chitosan in 1000mL 1wt% acetic acid solution, stir and mix evenly to obtain a chitosan solution; add 75g humic acid into 500mL deionized water, heat to 60°C in a water bath, stir and dissolve evenly to obtain a 15wt% humic acid solution; B2: Slowly add 500 mL of humic acid solution prepared in step B1 to 1000 mL of chitosan solution prepared in step B1, then add 4.25 g of glutaraldehyde, control the temperature at 30°C, stir and react for 2 h, centrifuge, filter, and vacuum dry at 60°C for 12 h to obtain chitosan-modified humic acid; The specific preparation steps of the multifunctional composite soil conditioner are as follows: S1: adding polyvinyl alcohol to 20 parts by weight of deionized water, stirring and dissolving uniformly to obtain a polyvinyl alcohol solution; adding polylactic acid to 30 parts by weight of dichloromethane, stirring and dissolving uniformly to obtain a polylactic acid solution; S2: adding lime powder to the polyvinyl alcohol solution prepared in step S1, stirring and dispersing evenly, then slowly adding it to the polylactic acid solution, controlling the pH to be neutral, stirring at 500 rpm for 3 hours, standing for 6 hours, centrifuging, filtering, and freeze-drying at -40°C for 24 hours to obtain coated lime powder; S3: adding nanocrystalline cellulose to 20 times the weight of deionized water, and dispersing the nanocrystalline cellulose evenly by ultrasonic treatment to obtain a nanocrystalline cellulose dispersion; adding the nanocrystalline cellulose dispersion to nano-silicon dioxide, and dispersing the nanocrystalline cellulose evenly by ultrasonic treatment, standing for 2 hours, and freeze-drying at -40°C for 24 hours to obtain a composite powder; S4: adding sodium alginate to 50 times the weight of deionized water, stirring and dissolving uniformly to obtain a sodium alginate solution; spraying the sodium alginate uniformly onto the coated lime powder prepared in step S2, stirring at 500 rpm for 30 min, spray drying, setting parameters as follows: inlet temperature 150° C., outlet temperature 80° C., atomization pressure 3 bar, to obtain slow-release lime particles; S5: uniformly mixing the modified biochar, diatomaceous earth, chitosan-modified humic acid, plant extract, the composite powder prepared in step S3, and the slow-release lime particles prepared in step S4 using a ball mill, and drying at 40° C. for 12 h to obtain a composite soil conditioner; The plant extract is prepared by extracting active ingredients from 0.6 parts of garlic, 0.5 parts of wormwood, 0.5 parts of mint, 0.6 parts of prickly ash, 0.5 parts of chili, 0.5 parts of perilla, 0.6 parts of tobacco, 0.8 parts of onion, 0.4 parts of star anise, 0.4 parts of neem leaves and 0.6 parts of bidens pilosa by conventional technical means and mixing them.

[0017] Example 2: A multifunctional composite soil conditioner, comprising component A and component B; the component A comprises the following components: 45 parts of modified biochar, 10 parts of diatomaceous earth, 4 parts of bentonite, 16 parts of chitosan-modified humic acid and 5 parts of nano-silicon dioxide; the component B comprises the following components: 10 parts of lime powder, 8 parts of polyvinyl alcohol, 8 parts of polylactic acid, 7 parts of nanocrystalline cellulose, 8 parts of plant extracts and 6 parts of sodium alginate.

[0018] The specific preparation steps of modified biochar are as follows: A1: Add 5 g of ferrous sulfate to 500 mL of deionized water, stir and mix well, adjust the pH to neutral with NaOH solution, and let it react at room temperature for 50 min to obtain a precursor iron solution; A2: Select corn stalks, crush, wash, dry at 80℃ for 18h, place in nitrogen environment, heat at 700℃ for 4h, cool naturally to room temperature, wash with deionized water, dry at 60℃ for 24h to obtain biochar; A3: Slowly add 400 mL of the precursor iron solution prepared in step A2 to 5 g of the biochar prepared in step A1, slowly add 1.3 g of sodium borohydride, stir and disperse evenly under nitrogen environment, let stand for 10 h, centrifuge, filter, and dry at 55 ° C for 12 h to obtain modified biochar; The specific preparation steps of chitosan modified humic acid are as follows: B1: Dissolve 10g chitosan in 800mL 1wt% acetic acid solution, stir and mix evenly to obtain a chitosan solution; add 60g humic acid into 600mL deionized water, heat to 60°C in a water bath, stir and dissolve evenly to obtain a 10wt% humic acid solution; B2: Slowly add 600 mL of humic acid solution prepared in step B1 to 800 mL of chitosan solution prepared in step B1, then add 3.5 g of glutaraldehyde, control the temperature at 35°C, stir and react for 1.5 h, centrifuge, filter, and vacuum dry at 60°C for 20 h to obtain chitosan-modified humic acid; The specific preparation steps of the multifunctional composite soil conditioner are as follows: S1: adding polyvinyl alcohol to 15 parts by weight of deionized water, stirring and dissolving uniformly to obtain a polyvinyl alcohol solution; adding polylactic acid to 25 parts by weight of dichloromethane, stirring and dissolving uniformly to obtain a polylactic acid solution; S2: adding lime powder to the polyvinyl alcohol solution prepared in step S1, stirring and dispersing evenly, then slowly adding it to the polylactic acid solution, controlling the pH to be neutral, stirring at 700 rpm for 2.5 hours, standing for 10 hours, centrifuging, filtering, and freeze-drying at -40°C for 24 hours to obtain coated lime powder; S3: adding nanocrystalline cellulose to 15 times the weight of deionized water, and dispersing it evenly by ultrasonic treatment to obtain a nanocrystalline cellulose dispersion; adding the nanocrystalline cellulose dispersion to nano-silicon dioxide, and dispersing it evenly by ultrasonic treatment, standing for 3 hours, and freeze-drying at -40°C for 24 hours to obtain a composite powder; S4: adding sodium alginate to 50 times the weight of deionized water, stirring and dissolving uniformly to obtain a sodium alginate solution; spraying the sodium alginate uniformly onto the coated lime powder prepared in step S2, stirring at 500 rpm for 30 min, spray drying, setting parameters as follows: inlet temperature 155°C, outlet temperature 85°C, atomization pressure 4 bar, to obtain slow-release lime particles; S5: uniformly mixing the modified biochar, diatomaceous earth, chitosan-modified humic acid, plant extract, the composite powder prepared in step S3, and the slow-release lime particles prepared in step S4 using a ball mill, and drying at 40° C. for 12 h to obtain a composite soil conditioner; The plant extract is prepared by extracting active ingredients from 0.8 parts of garlic, 0.8 parts of wormwood, 0.6 parts of mint, 0.8 parts of prickly ash, 0.7 parts of chili, 0.8 parts of perilla, 0.8 parts of tobacco, 0.9 parts of onion, 0.5 parts of star anise, 0.5 parts of chinaberry leaves and 0.8 parts of bidens pilosa by conventional technical means and mixing them.

[0019] Example 3: A multifunctional composite soil conditioner, comprising component A and component B; the component A comprises the following components: 50 parts of modified biochar, 12 parts of diatomaceous earth, 5 parts of bentonite, 18 parts of chitosan-modified humic acid and 6 parts of nano-silicon dioxide; the component B comprises the following components: 12 parts of lime powder, 10 parts of polyvinyl alcohol, 10 parts of polylactic acid, 8 parts of nanocrystalline cellulose, 10 parts of plant extracts and 8 parts of sodium alginate.

[0020] The specific preparation steps of modified biochar are as follows: A1: Add 5 g of ferrous sulfate to 500 mL of deionized water, stir and mix well, adjust the pH to neutral with NaOH solution, and let it react at room temperature for 60 min to obtain a precursor iron solution; A2: Select corn stalks, crush, wash, dry at 100℃ for 12h, place in nitrogen environment after drying, heat at 800℃ for 3h, cool naturally to room temperature, wash with deionized water, and dry at 60℃ for 24h to obtain biochar; A3: Slowly add 500 mL of the precursor iron solution prepared in step A2 to 5 g of the biochar prepared in step A1, slowly add 1.5 g of sodium borohydride, stir and disperse evenly under nitrogen environment, let stand for 12 hours, centrifuge, filter, and dry at 60°C for 12 hours to obtain modified biochar; The specific preparation steps of chitosan modified humic acid are as follows: B1: Dissolve 10g chitosan in 500mL 1wt% acetic acid solution, stir and mix evenly to obtain a chitosan solution; add 100g humic acid into 500mL deionized water, heat to 60°C in a water bath, stir and dissolve evenly to obtain a 20wt% humic acid solution; B2: Slowly add 500 mL of humic acid solution prepared in step B1 to 500 mL of chitosan solution prepared in step B1, then add 5.5 g of glutaraldehyde, control the temperature at 40°C, stir and react for 1 hour, centrifuge, filter, and vacuum dry at 60°C for 24 hours to obtain chitosan-modified humic acid; The specific preparation steps of the multifunctional composite soil conditioner are as follows: S1: adding polyvinyl alcohol to 20 parts by weight of deionized water, stirring and dissolving uniformly to obtain a polyvinyl alcohol solution; adding polylactic acid to 30 parts by weight of dichloromethane, stirring and dissolving uniformly to obtain a polylactic acid solution; S2: adding lime powder to the polyvinyl alcohol solution prepared in step S1, stirring and dispersing evenly, then slowly adding it to the polylactic acid solution, controlling the pH to be neutral, stirring at 800 rpm for 2 hours, standing for 12 hours, centrifuging, filtering, and freeze-drying at -40°C for 24 hours to obtain coated lime powder; S3: adding nanocrystalline cellulose to 20 times the weight of deionized water, and dispersing the nanocrystalline cellulose evenly by ultrasonic treatment to obtain a nanocrystalline cellulose dispersion; adding the nanocrystalline cellulose dispersion to nano-silicon dioxide, and dispersing the nanocrystalline cellulose evenly by ultrasonic treatment, standing for 4 hours, and freeze-drying at -40°C for 24 hours to obtain a composite powder; S4: adding sodium alginate to 50 times the weight of deionized water, stirring and dissolving uniformly to obtain a sodium alginate solution; spraying the sodium alginate uniformly onto the coated lime powder prepared in step S2, stirring at 500 rpm for 30 min, spray drying, setting parameters as follows: inlet temperature 160°C, outlet temperature 90°C, atomization pressure 5 bar, to obtain slow-release lime particles; S5: uniformly mixing the modified biochar, diatomaceous earth, chitosan-modified humic acid, plant extract, the composite powder prepared in step S3, and the slow-release lime particles prepared in step S4 using a ball mill, and drying at 40° C. for 12 h to obtain a composite soil conditioner; The plant extract is prepared by extracting active ingredients from 1 part of garlic, 0.9 part of wormwood, 0.9 part of mint, 1 part of prickly ash, 0.9 part of chili, 0.9 part of perilla, 1 part of tobacco, 1 part of onion, 0.6 part of star anise, 0.8 part of neem leaves and 1 part of bidens pilosa by conventional technical means and mixing them.

[0021] Comparative Example 1: The operation of Comparative Example 1 is basically the same as that of Example 2, except that in Comparative Example 1, nano zero-valent iron is not used to modify the biochar.

[0022] Comparative Example 2: The operation of Comparative Example 2 is substantially the same as that of Example 2, except that chitosan is not used to modify humic acid in Comparative Example 2.

[0023] Comparative Example 3: The operation of Comparative Example 3 is substantially the same as that of Example 2, except that polylactic acid and polyvinyl alcohol are not added in Comparative Example 3.

[0024] Comparative Example 4: The operation of Comparative Example 4 is basically the same as that of Example 2, except that no nano-silicon dioxide is added in Comparative Example 4.

[0025] Comparative Example 5: The operation of Comparative Example 5 is substantially the same as that of Example 2, except that nanocrystalline cellulose is not added in Comparative Example 5.

[0026] Performance Testing: Ecotoxicity test: The test was conducted using earthworms, and the earthworm culture medium was used as a reference to prepare a control group (blank control + heavy metal control) and a treatment group (composite soil conditioner treatment + composite soil conditioner and heavy metal treatment); the blank control was an earthworm culture medium without any treatment, and the heavy metal control was an earthworm culture medium containing a 10 mg / L heavy metal ion cadmium solution; the composite soil conditioner treatment was an earthworm culture medium to which 1 g of the composite soil conditioner prepared in Example 2 was added, and the composite soil conditioner and heavy metal treatment was an earthworm culture medium containing a 10 mg / L heavy metal ion cadmium solution and 1 g of Example 2. Prepared earthworm culture medium of composite soil conditioner; 120 earthworms were randomly allocated to the above four test groups, 120 earthworms in each group, and cultured at 20°C, pH 6.5 for 7 days, and the earthworm mortality rate was calculated (mortality rate (%) = (initial number - number after the test) × 100%), and the weight changes of earthworms were measured on the 2nd, 4th and 7th days (20 earthworms were randomly selected from each group for weighing, and the average weight change of the whole group was estimated and recorded, and the weight change percentage was calculated = (average weight after the test - average weight before the test) / average weight before the test × 100%), and the results are shown in Table 1 below.

[0027] Table 1. Ecotoxicity test results of composite soil conditioners

[0028] It can be seen from the results in Table 1 that the composite soil conditioner prepared by the present invention is safe and reliable, has no significant effect on earthworms, has extremely low ecotoxicity, and is safe and reliable; and it can be seen from the composite soil conditioner and heavy metal treatment groups that the composite soil conditioner prepared by the present invention has excellent adsorption performance for metal ions and can significantly improve the survival rate of earthworms.

[0029] Heavy metal adsorption test: prepare 10 mg / L standard solutions of arsenic, cadmium and lead, take 1 g of the composite soil conditioner prepared in Example 2 and Comparative Examples 1 to 5, respectively, add them to 100 mL of the standard solutions of arsenic, cadmium and lead prepared above, adjust the pH to 7, stir and mix evenly at 200 rpm at room temperature, let stand for 24 h, sample and calculate the adsorption rate at 0 h, 3 h, 6 h, 12 h, 24 h and 48 h (adsorption rate (%) = (initial concentration - concentration at sampling) / initial concentration × 100%), each test is repeated three times, and the average value is taken. The adsorption rate results of Example 2 and Comparative Examples 1 to 5 are as follows Figure 1 , 2 , as shown in Figure 3.

[0030] Depend on Figure 1 , Figure 2 and Figure 3 The results show that the composite soil conditioner prepared by the present invention utilizes the synergistic effect of multiple raw materials to exert excellent adsorption performance; from the results of Example 2 and Comparative Example 1, it can be seen that the lack of the synergistic effect of nano zero-valent iron has a significant impact on the adsorption efficiency, especially the decrease in the adsorption rate of arsenic is more obvious; from the results of Example 2 and Comparative Example 2, it can be seen that the lack of chitosan-modified humic acid weakens the chelating ability of heavy metals, and the adsorption rates of arsenic and cadmium decrease significantly, and the adsorption rate is significantly reduced; from the results of Comparative Example 3 and Example 2, it can be seen that the lack of polylactic acid and polyvinyl alcohol causes the sustained-release structure of lime powder to fail, and the lime release The rate is accelerated, resulting in unstable pH adjustment, and pH fluctuations may occur, affecting the adsorption behavior of heavy metals, thereby resulting in a decrease in adsorption efficiency; from the results of Comparative Example 4 and Example 2, it can be seen that the lack of nano-silicon dioxide affects the construction of the three-dimensional adsorption network, the fixation capacity of heavy metals decreases, and the stability and active life of nano-zero-valent iron may be affected, thereby causing its reduction ability and heavy metal conversion ability to be affected to a certain extent; from the results of Comparative Example 5 and Example 2, it can be seen that the lack of nanocrystalline cellulose causes the stability and efficiency of the three-dimensional adsorption network to decrease, resulting in a slight weakening of the heavy metal adsorption capacity.

[0031] Soil improvement test: The composite soil conditioner prepared in Example 2 and Comparative Examples 1 to 5 was added to acidified soil with a pH of 4.5, placed in an environmental simulator, maintained at a temperature of 25°C and a humidity of 60%, and the soil pH values ​​at the 1st, 2nd, 3rd and 6th month were recorded. The results are as follows: Figure 4 shown.

[0032] Depend on Figure 4 The results show that the composite soil conditioner prepared by the present invention has excellent soil acidification repair function, and can effectively alleviate the acidity of acidified soil to neutrality; from the results of Comparative Example 2 and Example 2, it can be seen that the chelation effect and microbial environment optimization performance are significantly affected by the lack of chitosan-modified humic acid; from the results of Comparative Example 3 and Example 2, it can be seen that the pH value fluctuates greatly in the early stage due to the lack of sustained-release structure, and the improvement effect in the later stage is insufficient.

[0033] Spectrum test: The SEM scanning electron microscope spectrum of the composite soil conditioner prepared in Example 2 was observed using a scanning electron microscope. The results are as follows: Figure 5 shown.

[0034] Depend on Figure 5The results show that the complex porous network structure can be clearly seen in the image. This pore distribution helps to provide abundant adsorption sites, which is beneficial to the fixation of heavy metals. The granular features in the image represent the distribution of nano-silica. These particles are evenly distributed and embedded in the porous structure. There is an obvious fibrous mesh interwoven structure in the image, covering the porous surfaces, which is in line with expectations.

[0035] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A multifunctional composite soil conditioner, characterized in that: The composition includes component A and component B; the component A includes the following components: 35-50 parts of modified biochar, 8-12 parts of diatomaceous earth, 3-5 parts of bentonite, 13-18 parts of chitosan modified humic acid and 4-6 parts of nano silicon dioxide; the component B includes the following components: 8-12 parts of lime powder, 5-10 parts of polyvinyl alcohol, 5-10 parts of polylactic acid, 5-8 parts of nanocrystalline cellulose, 6-10 parts of plant extract and 5-8 parts of sodium alginate; The plant extract is prepared by extracting active ingredients from 0.6-1 parts of garlic, 0.5-0.9 parts of wormwood, 0.5-0.9 parts of mint, 0.6-1 parts of prickly ash, 0.5-0.9 parts of chili, 0.5-0.9 parts of perilla, 0.6-1 parts of tobacco, 0.8-1 parts of onion, 0.4-0.6 parts of star anise, 0.4-0.8 parts of chinaberry leaves and 0.6-1 parts of bidens pilosa by conventional technical means and mixing them.

2. A multifunctional composite soil conditioner according to claim 1, characterized in that: The specific preparation steps of the modified biochar are as follows: A1: Add ferrous sulfate to deionized water, stir and mix evenly, adjust the pH to neutral with NaOH solution, and let it stand at room temperature to react to obtain a precursor iron solution; A2: Select corn stalks, crush, wash, and dry them. After drying, place them in a nitrogen environment, heat them, cool them naturally to room temperature, wash them with deionized water, and dry them to obtain biochar; A3: Slowly add the precursor iron solution prepared in step A2 to the biochar prepared in step A1, slowly add sodium borohydride, stir and disperse evenly under a nitrogen environment, let stand, centrifuge, filter, and dry to obtain modified biochar.

3. A multifunctional composite soil conditioner according to claim 2, characterized in that: In step A1, the ratio of the amount of ferrous sulfate to deionized water is 1 g:100 mL:0.2-0.3 g.

4. A multifunctional composite soil conditioner according to claim 3, characterized in that: In step A3, the ratio of the amount of the precursor iron solution, biochar and sodium borohydride is 6-10 mL: 1 g: 0.2-0.3 g.

5. A multifunctional composite soil conditioner according to claim 4, characterized in that: The specific preparation steps of the chitosan modified humic acid are as follows: B1: Dissolve chitosan in 1wt% acetic acid solution, stir and mix evenly to obtain a chitosan solution; add humic acid into deionized water, heat in a water bath, stir and dissolve evenly to obtain a humic acid solution; B2: slowly add the humic acid solution prepared in step B1 to the chitosan solution prepared in step B1, then add glutaraldehyde, control the temperature at 30-40° C., stir to react, centrifuge, filter, and vacuum dry to obtain chitosan-modified humic acid.

6. A multifunctional composite soil conditioner according to claim 5, characterized in that: In step B1, the ratio of the chitosan to the acetic acid solution is 1-2 g:100 mL.

7. A multifunctional composite soil conditioner according to claim 6, characterized in that: In step B2, the volume ratio of the humic acid solution to the chitosan solution is 1:1-2; the amount of glutaraldehyde used is 5% of the total mass of the humic acid and chitosan substrates.

8. A method for preparing the multifunctional composite soil conditioner according to any one of claims 1 to 7, characterized in that: The specific preparation steps are as follows: S1: adding polyvinyl alcohol to deionized water, stirring and dissolving uniformly to obtain a polyvinyl alcohol solution; adding polylactic acid to dichloromethane, stirring and dissolving uniformly to obtain a polylactic acid solution; S2: adding lime powder to the polyvinyl alcohol solution prepared in step S1, stirring and dispersing it evenly, and then slowly adding it to the polylactic acid solution, controlling the pH to neutral, stirring, standing, centrifuging, filtering, and freeze-drying to obtain coated lime powder; S3: adding nanocrystalline cellulose to deionized water, dispersing it evenly by ultrasonic treatment, and obtaining a nanocrystalline cellulose dispersion; adding the nanocrystalline cellulose dispersion to nano-silicon dioxide, dispersing it evenly by ultrasonic treatment, standing it, and freeze-drying it to obtain a composite powder; S4: adding sodium alginate to deionized water, stirring and dissolving uniformly to obtain a sodium alginate solution; spraying the sodium alginate uniformly onto the coated lime powder prepared in step S2, stirring, spray drying, and obtaining slow-release lime particles; S5: uniformly mixing the modified biochar, diatomaceous earth, chitosan-modified humic acid, plant extract, the composite powder prepared in step S3 and the slow-release lime particles prepared in step S4 using a ball mill, and vacuum drying to obtain a composite soil conditioner.

9. The method for preparing a multifunctional composite soil conditioner according to claim 8, characterized in that: In step S4, the spray drying parameters are: inlet temperature 150-160°C, outlet temperature 80-90°C, and atomization pressure 3-5 bar.

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