Environment-friendly soil improvement and remediation agent and preparation method thereof

Abstract

The present application relates to the technical field of soil remediation, and discloses an environment-friendly soil improvement and remediation agent and a preparation method thereof, the remediation agent is composed of 30-50 parts of biochar, 15-25 parts of humic acid, 2-3 parts of modified attapulgite, 1-1.5 parts of citric acid grafted ramie fiber, 5-10 parts of compound microbial inoculant, 8-15 parts of organic slow-release fertilizer, 5-10 parts of zeolite powder, 3-8 parts of plant source chelating agent and 2-5 parts of pH regulator according to weight parts. The preparation process comprises the steps of raw material pretreatment, initial mixing, remixing, granulation and drying, and the product performance is stable by precisely controlling the crushing particle size, mixing speed and drying temperature. The remediation agent integrates the functions of heavy metal passivation, salt and alkali neutralization, soil loosening and nutrient supplement, the preparation process is green and pollution-free, the remediation effect is durable and there is no secondary pollution, the soil physical and chemical properties can be effectively improved, the soil fertility can be improved, and the sustainable development of agriculture and the improvement of ecological environment can be promoted.

Description

Technical Field

[0001] This invention relates to the field of soil remediation technology, specifically to an environmentally friendly soil amendment and remediation agent and its preparation method. Background Technology

[0002] With the acceleration of industrialization, the excessive use of chemical fertilizers and pesticides in agricultural production, and the unreasonable exploitation of mineral resources, soil pollution problems have become increasingly prominent. These problems are mainly manifested in soil acidification and degradation, excessive heavy metals, aggravated salinization, soil compaction, decreased organic matter content, and nutrient imbalance. These issues seriously affect the growth, development, yield, and quality of crops, and even endanger human health through the food chain, thus hindering the sustainable development of agriculture and the improvement of the ecological environment.

[0003] Currently, soil remediation technologies mainly fall into three categories: physical remediation, chemical remediation, and bioremediation. Physical remediation methods, such as topsoil replacement and soil washing, have drawbacks such as large engineering scale, high cost, and the potential for secondary pollution. Chemical remediation methods reduce the activity of pollutants in the soil by adding chemical chelating agents and amendments, but commonly used chemical agents are mostly synthetic substances that tend to remain in the soil, disrupting the soil microbial community structure and affecting the soil ecological balance. While bioremediation methods are more environmentally friendly, they have long remediation cycles and low efficiency, making it difficult to meet the needs of rapid remediation of large areas of contaminated soil.

[0004] Therefore, there is an urgent need to develop an environmentally friendly soil amendment and remediation agent that uses environmentally friendly and renewable raw materials, has multiple remediation functions, provides long-lasting remediation effects, and does not cause secondary pollution. Summary of the Invention

[0005] (a) Technical problems to be solved

[0006] To address the shortcomings of existing technologies, this invention provides an environmentally friendly soil amendment and remediation agent and its preparation method, which has multiple functions including heavy metal passivation, salinity neutralization, soil loosening, and nutrient replenishment, and the preparation process is green and environmentally friendly.

[0007] (II) Technical Solution

[0008] To achieve the above objectives, the present invention provides the following technical solution: an environmentally friendly soil amendment and remediation agent, comprising, by weight, the following raw materials: 30-50 parts biochar, 15-25 parts humic acid, 2-3 parts modified attapulgite, 1-1.5 parts citric acid-grafted ramie fiber, 5-10 parts compound microbial inoculant, 8-15 parts organic slow-release fertilizer, 5-10 parts zeolite powder, 3-8 parts plant-derived chelating agent, and 2-5 parts pH adjuster.

[0009] Furthermore, the biochar is made from crop straw, forestry waste, or livestock manure through high-temperature anaerobic carbonization at a temperature of 450-650℃ and a carbonization time of 2-4 hours, with a specific surface area of ​​150-300 m² / g and a pore size of 2-10 nm; the crop straw includes one or more of corn straw, wheat straw, and rice straw, and the forestry waste includes one or more of dead branches, fallen leaves, and sawdust.

[0010] Further, the modified attapulgite is prepared as follows: 4-5g of attapulgite is pulverized to 100-200 mesh, and 5-8 times its mass of deionized water is added, and the mixture is stirred and dispersed to form a suspension; 3-6% by mass of aluminum sulfate and 2-5% by mass of polyacrylamide are added to the suspension, and the mixture is stirred and reacted at 50-70℃ for 1-2 hours; after the reaction is completed, the mixture is filtered and washed until the filtrate is neutral, and then dried at 105-115℃ for 3-5 hours.

[0011] Furthermore, the compound microbial agent is prepared by mixing Bacillus subtilis, phosphate-solubilizing bacteria, potassium-solubilizing bacteria, nitrogen-fixing bacteria, and Saccharomyces cerevisiae in a mass ratio of 3:2:2:2:1, with an effective viable count ≥2.0 × 10⁻⁶. 9 cfu / g.

[0012] Furthermore, the organic slow-release fertilizer is made by mixing well-rotted livestock and poultry manure, soybean meal, bone meal and modified chitosan in a mass ratio of 5:3:1:1, wherein the organic matter content is ≥40% and the total nitrogen, phosphorus and potassium content is ≥8%.

[0013] Furthermore, the plant-derived chelating agent is one or more of citric acid, malic acid, or tea saponin, with a purity ≥95%; the pH adjuster is one or more of wood ash, dolomite powder, or gypsum powder, with a particle size of 100-200 mesh.

[0014] Furthermore, the preparation method of the environmentally friendly soil amendment and remediation agent is as follows:

[0015] (1) Raw material pretreatment: Crush biochar, humic acid and zeolite powder to 100-200 mesh and sieve them; crush organic slow-release fertilizer to 80-120 mesh and sieve it for later use;

[0016] (2) Initial mixing: Add the pretreated biochar, humic acid, zeolite powder, modified attapulgite, citric acid-grafted ramie fiber, and organic slow-release fertilizer into a double-screw mixer and mix for 20-30 minutes at a speed of 150-200 r / min to obtain the initial mixed material.

[0017] (3) Compound mixing: Add plant-derived chelating agent and pH adjuster to the initial mixture and continue mixing at 180-220 r / min for 15-25 min; then add compound microbial agent and mix at low speed at 80-120 r / min for 5-10 min to obtain the mixture.

[0018] (4) Granulation and drying: The mixture is fed into a disc granulator, and deionized water is sprayed to adjust the humidity of the material. The mixture is granulated to form particles with a diameter of 2-5 mm. The particles are then fed into a low-temperature dryer and dried at 40-50℃ until the moisture content is ≤8%, thus obtaining an environmentally friendly soil amendment and remediation agent.

[0019] Furthermore, in step (4), the material humidity is adjusted to 20-30%.

[0020] (III) Beneficial technical effects:

[0021] In this invention, the highly porous structure of biochar provides ample adsorption sites. Plant-derived chelating agents (citric acid, malic acid, etc.) form stable chelates with heavy metal ions. Modified attapulgite soil, after modification with aluminum sulfate and polyacrylamide, exhibits enhanced adsorption performance. The synergistic effect of these three components reduces the available content of heavy metals such as lead and cadmium in the soil, significantly decreasing the migration of heavy metals to crop roots. The chelated and adsorbed states formed by heavy metals and the remediation agent are stable and will not be released again due to changes in the soil environment. This solves the problems of easy decomposition and heavy metal rebound associated with traditional chemical chelating agents, and long-term use can sustainably reduce the risk of heavy metal pollution in soil.

[0022] In this technical solution, citric acid-grafted ramie fiber possesses excellent fiber toughness and porous structure. Working synergistically with biochar and zeolite powder, it reduces soil bulk density, increases porosity, breaks up soil aggregates, enhances soil aeration and water permeability, and promotes crop root extension. The porous structure of biochar, modified attapulgite, and humic acid exhibits strong water and fertilizer retention properties, increasing soil water retention and reducing irrigation water consumption. Simultaneously, it adsorbs and stores nutrient molecules in the soil, reducing leaching losses of nitrogen, phosphorus, potassium, and other nutrients, and extending nutrient availability. The organic slow-release fertilizer is made by mixing well-rotted livestock and poultry manure, soybean meal, and other natural raw materials with modified chitosan in a specific ratio. The coating structure formed by the modified chitosan controls the nutrient release rate, extending the nutrient release cycle and avoiding the "seedling burn" and rapid nutrient loss problems associated with traditional chemical fertilizers. This meets the differentiated nutrient needs of crops during the seedling, growth, and fruiting stages. Biochar, humic acid, and well-rotted livestock and poultry manure are rich in natural organic matter. Their application can increase soil organic matter content, replenish the soil carbon pool, promote soil microbial activity and material cycling, and long-term use can reverse soil degradation trends, achieving sustainable improvement in soil fertility. The biochar in this invention is derived from agricultural and forestry solid waste such as crop straw and forestry waste, while the organic slow-release fertilizer uses well-rotted livestock and poultry manure as its main component, realizing the resource utilization of waste and reducing environmental pollution caused by solid waste incineration and landfill. All raw materials are natural or bio-based, containing no artificially synthesized toxic or harmful substances. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] For the preparation of modified chitosan, referring to the literature "Homogeneous Synthesis and Characterization of Chitosan / Polycaprolactone Graft Copolymer", appropriate amounts of ε-caprolactone and catalyst Sn(OCt)2 were weighed and added to a chitosan / [BMIM]Ac solution. The reaction was continued under N2 atmosphere at the appropriate temperature with stirring. After the reaction was completed, the solution was cooled to room temperature and 3-5 times the volume of ethanol was added to precipitate the graft copolymer. The precipitate was repeatedly washed with ethanol and collected. The product was extracted with toluene as the extractant using a Soxhlet extractor until the caprolactone homopolymer was completely removed. The obtained graft copolymer was dried in a vacuum drying oven at 80℃ for 24 h.

[0025] The method for preparing citric acid-grafted ramie fiber is as follows: 1 g of dried ramie fiber is placed in 100 mL of 18% sodium hydroxide aqueous solution and treated at room temperature for 3 h. Then, it is washed with water until neutral and dried at 60 °C for 12 h for later use. The pretreated ramie fiber is mixed with 100 mL of 20 mmol citric acid solution and sodium hypophosphite (0.4 g) is added. After stirring at room temperature for 30 min, it is dried at 60 °C for 24 h to remove water. Then, it is heated to 120 °C for esterification reaction for 90 min. After cooling to room temperature, it is washed with water until neutral and dried at 60 °C to obtain citric acid-grafted ramie fiber.

[0026] Example 1:

[0027] An environmentally friendly soil amendment and remediation agent, by weight, comprises the following raw materials: 30 parts biochar, 15 parts humic acid, 2 parts modified attapulgite, 1 part citric acid-grafted ramie fiber, 5 parts compound microbial inoculant, 8 parts organic slow-release fertilizer, 5 parts zeolite powder, 3 parts plant-derived chelating agent, and 2 parts pH adjuster.

[0028] The biochar is made from crop straw through high-temperature anaerobic carbonization at a temperature of 450℃ for 2 hours, with a specific surface area of ​​150 m² / g and a pore size of 2 nm; the crop straw is corn straw.

[0029] The modified attapulgite is prepared as follows: 4g of attapulgite is crushed to 100 mesh, and 5 times its weight of deionized water is added. The mixture is stirred and dispersed to form a suspension. 3% aluminum sulfate and 2% polyacrylamide by weight of the attapulgite are added to the suspension, and the mixture is stirred and reacted at 50°C for 1 hour. After the reaction is completed, the mixture is filtered and washed until the filtrate is neutral. The filtrate is then dried at 105°C for 3 hours.

[0030] The compound microbial agent is prepared by mixing Bacillus subtilis, phosphate-solubilizing bacteria, potassium-solubilizing bacteria, nitrogen-fixing bacteria, and Saccharomyces cerevisiae in a mass ratio of 3:2:2:2:1, with an effective viable count ≥2.0×10⁻⁶. 9 cfu / g.

[0031] The organic slow-release fertilizer is made by mixing well-rotted livestock and poultry manure, soybean meal, bone meal and modified chitosan in a mass ratio of 5:3:1:1, wherein the organic matter content is ≥40% and the total nitrogen, phosphorus and potassium content is ≥8%.

[0032] The plant-derived chelating agent is citric acid with a purity of ≥95%; the pH adjuster is wood ash with a particle size of 100 mesh.

[0033] The preparation method of the environmentally friendly soil amendment and remediation agent is as follows:

[0034] (1) Raw material pretreatment: The biochar, humic acid and zeolite powder are crushed to 100 mesh and sieved; the organic slow-release fertilizer is crushed to 80 mesh and sieved for later use.

[0035] (2) Initial mixing: The pretreated biochar, humic acid, zeolite powder, modified attapulgite, citric acid-grafted ramie fiber, and organic slow-release fertilizer are added to a double-helix mixer and mixed for 20 minutes at a speed of 150 r / min to obtain the initial mixed material.

[0036] (3) Compound mixing: Add plant-derived chelating agent and pH adjuster to the initial mixture and continue mixing at 180 r / min for 15 min; then add compound microbial agent and mix at low speed at 80 r / min for 5 min to obtain the mixture.

[0037] (4) Granulation and drying: The mixture is fed into a disc granulator, and deionized water is sprayed to adjust the material humidity to 20% to form particles with a particle size of 2mm. The particles are then fed into a low-temperature dryer and dried at 40℃ until the moisture content is ≤8% to obtain an environmentally friendly soil amendment and remediation agent.

[0038] Example 2:

[0039] An environmentally friendly soil amendment and remediation agent, by weight, comprises the following raw materials: 50 parts biochar, 25 parts humic acid, 3 parts modified attapulgite soil, 1.5 parts citric acid-grafted ramie fiber, 10 parts compound microbial agent, 15 parts organic slow-release fertilizer, 10 parts zeolite powder, 8 parts plant-derived chelating agent, and 5 parts pH adjuster.

[0040] The biochar is made from crop straw through high-temperature anaerobic carbonization at a temperature of 650℃ for 4 hours, with a specific surface area of ​​300 m² / g and a pore size of 10 nm; the crop straw is wheat straw.

[0041] The modified attapulgite is prepared as follows: 5g of attapulgite is crushed to 200 mesh, and 8 times its weight of deionized water is added. The mixture is stirred and dispersed to form a suspension. 6% aluminum sulfate and 5% polyacrylamide by weight of the attapulgite are added to the suspension, and the mixture is stirred and reacted at 70°C for 2 hours. After the reaction is completed, the mixture is filtered and washed until the filtrate is neutral. The filtrate is then dried at 115°C for 5 hours.

[0042] The compound microbial agent is prepared by mixing Bacillus subtilis, phosphate-solubilizing bacteria, potassium-solubilizing bacteria, nitrogen-fixing bacteria, and Saccharomyces cerevisiae in a mass ratio of 3:2:2:2:1, with an effective viable count ≥2.0×10⁻⁶. 9 cfu / g.

[0043] The organic slow-release fertilizer is made by mixing well-rotted livestock and poultry manure, soybean meal, bone meal and modified chitosan in a mass ratio of 5:3:1:1, wherein the organic matter content is ≥40% and the total nitrogen, phosphorus and potassium content is ≥8%.

[0044] The plant-derived chelating agent is malic acid with a purity of ≥95%; the pH adjuster is dolomite powder with a particle size of 200 mesh.

[0045] The preparation method of the environmentally friendly soil amendment and remediation agent is as follows:

[0046] (1) Raw material pretreatment: The biochar, humic acid and zeolite powder are crushed to 200 mesh and sieved; the organic slow-release fertilizer is crushed to 120 mesh and sieved for later use.

[0047] (2) Initial mixing: The pretreated biochar, humic acid, zeolite powder, modified attapulgite, citric acid-grafted ramie fiber, and organic slow-release fertilizer are added to a double-helix mixer and mixed for 30 minutes at a speed of 200 r / min to obtain the initial mixed material.

[0048] (3) Compound mixing: Add plant-derived chelating agent and pH adjuster to the initial mixture and continue mixing at 220 r / min for 25 min; then add compound microbial agent and mix at 120 r / min for 10 min to obtain the mixture.

[0049] (4) Granulation and drying: The mixture is fed into a disc granulator, and deionized water is sprayed to adjust the material humidity to 30% to form particles with a particle size of 5mm. The particles are then fed into a low-temperature dryer and dried at 50℃ until the moisture content is ≤8% to obtain an environmentally friendly soil amendment and remediation agent.

[0050] Example 3:

[0051] An environmentally friendly soil amendment and remediation agent, by weight, comprises the following raw materials: 40 parts biochar, 20 parts humic acid, 2.5 parts modified attapulgite, 1.2 parts citric acid-grafted ramie fiber, 7 parts compound microbial inoculant, 12 parts organic slow-release fertilizer, 8 parts zeolite powder, 5.5 parts plant-derived chelating agent, and 3.5 parts pH adjuster.

[0052] The biochar is made from crop straw, forestry waste, or livestock manure through high-temperature anaerobic carbonization at a temperature of 500℃ for 3 hours, with a specific surface area of ​​200 m² / g and a pore size of 6 nm; the crop straw is rice straw.

[0053] The modified attapulgite is prepared as follows: 4.5g of attapulgite is crushed to 150 mesh, and 6 times its mass of deionized water is added. The mixture is stirred and dispersed to form a suspension. 5% aluminum sulfate and 4% polyacrylamide by mass of attapulgite are added to the suspension, and the mixture is stirred and reacted at 60°C for 1.5h. After the reaction is completed, the mixture is filtered and washed until the filtrate is neutral. The filtrate is then dried at 110°C for 4h.

[0054] The compound microbial agent is prepared by mixing Bacillus subtilis, phosphate-solubilizing bacteria, potassium-solubilizing bacteria, nitrogen-fixing bacteria, and Saccharomyces cerevisiae in a mass ratio of 3:2:2:2:1, with an effective viable count ≥2.0×10⁻⁶. 9 cfu / g.

[0055] The organic slow-release fertilizer is made by mixing well-rotted livestock and poultry manure, soybean meal, bone meal and modified chitosan in a mass ratio of 5:3:1:1, wherein the organic matter content is ≥40% and the total nitrogen, phosphorus and potassium content is ≥8%.

[0056] The plant-derived chelating agent is malic acid with a purity of ≥95%; the pH adjuster is gypsum powder with a particle size of 150 mesh.

[0057] The preparation method of the environmentally friendly soil amendment and remediation agent is as follows:

[0058] (1) Raw material pretreatment: The biochar, humic acid and zeolite powder are crushed to 150 mesh and sieved; the organic slow-release fertilizer is crushed to 100 mesh and sieved for later use.

[0059] (2) Initial mixing: The pretreated biochar, humic acid, zeolite powder, modified attapulgite, citric acid-grafted ramie fiber, and organic slow-release fertilizer are added to a double-helix mixer and mixed for 25 minutes at a speed of 170 r / min to obtain the initial mixed material.

[0060] (3) Compound mixing: Add plant-derived chelating agent and pH adjuster to the initial mixture and continue mixing at 200 r / min for 20 min; then add compound microbial agent and mix at 100 r / min for 7 min to obtain the mixture.

[0061] (4) Granulation and drying: The mixture is fed into a disc granulator, and deionized water is sprayed to adjust the material humidity to 25% to form particles with a particle size of 3mm. The particles are then fed into a low-temperature dryer and dried at 45℃ until the moisture content is ≤8% to obtain an environmentally friendly soil amendment and remediation agent.

[0062] Comparative Example 1:

[0063] The difference between this comparative example and Example 3 is that attapulgite soil was used instead of modified attapulgite soil.

[0064] Comparative Example 2:

[0065] The difference between this comparative example and Example 3 is that ramie fiber was used instead of citric acid-grafted ramie fiber.

[0066] Comparative Example 3:

[0067] The difference between this comparative example and Example 3 is that chitosan was used instead of modified chitosan.

[0068] Comparative Example 4:

[0069] The difference between this comparative example and Example 3 is that only 40 parts of biochar with the same specifications as in Example 3 were used, without any other ingredients added.

[0070] Test soils: Two typical degraded soil types were selected: heavy metal contaminated saline-alkali land (soil A) and acidic compacted soil (soil B). Initial physicochemical and pollution indicators are as follows: | Soil type | Lead content (mg / kg) | Cadmium content (mg / kg) | pH value | Bulk density (g / cm³) | Organic matter content (%) | Total nitrogen, phosphorus, and potassium content (%) | Viable bacteria count (×10⁻⁶) 9 CFU / g) | Porosity (%) |

[0071] |Soil A (Heavy Metal Contaminated Saline-Alkali Land)|810|5.1|8.8|1.53|1.12|0.76|0.43|34.5|

[0072] Soil B (Acidic Compacted Soil) | 790 | 4.9 | 5.0 | 1.62 | 0.96 | 0.73 | 0.41 | 32.8 |

[0073] Experimental design: The amount of remediation agent applied in each embodiment and comparative example was 5% of the soil mass. A blank control group (without any remediation agent applied) was set up. Each group was replicated in three parallel steps. After culturing for 60 days under normal temperature, pressure and natural light conditions, various indicators were measured and the average value was taken as the final result.

[0074] Detection methods: The content of available heavy metals was determined by DTPA extraction; soil pH was determined by potentiometric method; soil bulk density was determined by ring cutter method; organic matter content was determined by potassium dichromate oxidation-external heating method; total nitrogen, phosphorus and potassium content was determined by a combination of Kjeldahl nitrogen determination method, molybdenum antimony colorimetric method and flame photometry; viable bacteria count was determined by plate count method; soil porosity was calculated based on bulk density and specific gravity.

[0075] Table 1. Experimental data of heavy metal contaminated saline-alkali land (soil A)

[0076]

[0077] Table 2 Experimental data of acidic compacted soil (soil B)

[0078]

[0079] Tables 1 and 2 show that Comparative Example 1 (unmodified attapulgite soil replacing modified attapulgite soil) exhibited significantly reduced heavy metal passivation and soil looseness, indicating that the attapulgite soil modified with aluminum sulfate and polyacrylamide had stronger adsorption capacity and made a significant contribution to heavy metal passivation and soil structure improvement. Comparative Example 2 (ramie fiber replacing citric acid-grafted ramie fiber) showed higher soil bulk density and lower porosity, indicating that citric acid grafting modification can enhance the structural stability and porosity of ramie fiber, making it more effective in breaking up soil compaction. Comparative Example 3 (chitosan replacing modified chitosan) showed a significant reduction in total nitrogen, phosphorus, and potassium content, proving that the coating effect of modified chitosan can effectively delay nutrient release and improve fertilizer utilization, while unmodified chitosan cannot achieve a highly efficient slow-release effect. Comparative Example 4 (single biochar) had the worst performance across all indicators, only slightly improving soil organic matter and porosity, with no significant effects on heavy metal passivation and fertility enhancement, highlighting the necessity of the multi-component synergistic design of this invention.

[0080] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0081] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

[0082] Those skilled in the art should understand that the above descriptions are merely several specific embodiments of the present invention, and not all embodiments.

Claims

1. An environmentally friendly soil conditioner and remediation agent, characterized in that, By weight, the raw material composition includes: 30-50 parts biochar, 15-25 parts humic acid, 2-3 parts modified attapulgite, 1-1.5 parts citric acid-grafted ramie fiber, 5-10 parts compound microbial inoculant, 8-15 parts organic slow-release fertilizer, 5-10 parts zeolite powder, 3-8 parts plant-derived chelating agent, and 2-5 parts pH adjuster. The modified attapulgite is prepared as follows: 4-5g of attapulgite is pulverized to 100-200 mesh, and 5-8 times its weight of deionized water is added. The mixture is stirred and dispersed to form a suspension. 3-6% aluminum sulfate and 2-5% polyacrylamide by weight of the attapulgite are added to the suspension, and the mixture is stirred and reacted at 50-70℃ for 1-2 hours. After the reaction is complete, the mixture is filtered and washed until the filtrate is neutral. The filtrate is then dried at 105-115℃ for 3-5 hours. The organic slow-release fertilizer is made by mixing well-rotted livestock and poultry manure, soybean meal, bone meal and modified chitosan in a mass ratio of 5:3:1:1, wherein the organic matter content is ≥40% and the total nitrogen, phosphorus and potassium content is ≥8%; Preparation of modified chitosan: Weigh ε-caprolactone and catalyst Sn(OCt)2, add them to chitosan / [BMIM]Ac solution, and continue to stir the reaction under N2 atmosphere. After the reaction is completed, cool the solution to room temperature and add 3-5 times the amount of ethanol to precipitate the graft copolymer. Wash repeatedly with ethanol, collect the precipitate, and use toluene as the extractant to extract the product with a Soxhlet extractor until the caprolactone homopolymer is completely removed. The obtained graft copolymer is dried in a vacuum drying oven at 80℃ for 24h. The method for preparing citric acid-grafted ramie fiber is as follows: 1g of dried ramie fiber is placed in 100mL of 18% sodium hydroxide aqueous solution and treated at room temperature for 3h. Then, it is washed with water until neutral and dried at 60℃ for 12h for later use. The pretreated ramie fiber is mixed with 100mL of 20mmol citric acid solution and 0.4g of sodium hypophosphite is added. After stirring at room temperature for 30min, it is dried at 60℃ for 24h to remove water. Then, it is heated to 120℃ for esterification reaction for 90min. After cooling to room temperature, it is washed with water until neutral and dried at 60℃ to obtain citric acid-grafted ramie fiber.

2. The environmentally friendly soil conditioner and remediation agent according to claim 1, characterized in that, The biochar is made from crop straw, forestry waste, or livestock manure through high-temperature anaerobic carbonization. The carbonization temperature is 450-650℃, the carbonization time is 2-4h, the specific surface area is 150-300m² / g, and the pore size is 2-10nm. The crop straw includes one or more of corn straw, wheat straw, and rice straw, and the forestry waste includes one or more of dead branches, fallen leaves, and sawdust.

3. The environmentally friendly soil conditioner and remediation agent according to claim 1, characterized in that, The plant-derived chelating agent is one or more of citric acid, malic acid, or tea saponin, with a purity ≥95%; the pH adjuster is one or more of wood ash, dolomite powder, or gypsum powder, with a particle size of 100-200 mesh.

4. The preparation method of the environmentally friendly soil amendment and remediation agent according to claim 1, characterized in that, The preparation method of the environmentally friendly soil amendment and remediation agent is as follows: (1) Raw material pretreatment: Crush biochar, humic acid and zeolite powder to 100-200 mesh and sieve them; crush organic slow-release fertilizer to 80-120 mesh and sieve it for later use; (2) Initial mixing: Add the pretreated biochar, humic acid, zeolite powder, modified attapulgite, citric acid-grafted ramie fiber, and organic slow-release fertilizer into a double-screw mixer and mix for 20-30 minutes at a speed of 150-200 r / min to obtain the initial mixed material. (3) Compound mixing: Add plant-derived chelating agent and pH adjuster to the initial mixture and continue mixing at 180-220 r / min for 15-25 min; then add compound microbial agent and mix at low speed at 80-120 r / min for 5-10 min to obtain the mixture. (4) Granulation and drying: The mixture is fed into a disc granulator, and deionized water is sprayed to adjust the humidity of the material. The mixture is granulated to form particles with a diameter of 2-5 mm. The particles are then fed into a low-temperature dryer and dried at 40-50℃ until the moisture content is ≤8%, thus obtaining an environmentally friendly soil amendment and remediation agent.

5. The preparation method of the environmentally friendly soil amendment and remediation agent according to claim 4, characterized in that, In step (4), the material moisture content is adjusted to 20-30%.

Images