Geniposide granules for soil remediation and a preparation method thereof

Abstract

This invention discloses a geniposide granule for soil remediation and its preparation method, relating to the field of soil improvement technology. The preparation method involves micro-encapsulating geniposide with sodium humate and polyglutamic acid, then mixing and granulating it with urea and 2-tolylthioformamide-modified biochar, dolomite powder, and composite phosphate to prepare geniposide granules for soil remediation. The active groups such as hydroxyl and carboxyl groups in geniposide complex heavy metals, protect soil enzymes, and promote organic matter accumulation. The urea and 2-tolylthioformamide-modified biochar achieves nitrogen and sulfur dual doping and a hierarchical porous structure, significantly enhancing adsorption and complexation capabilities. The ternary composite phosphate provides synergistic effects of precipitation passivation, nutrient supply, and complexation stabilization. Sodium humate and polyglutamic acid micro-encapsulate and slowly release geniposide, combined with gradient granulation and drying, to obtain stable granules with high heavy metal removal rates, increased organic matter content, and enhanced enzyme activity.

Description

Technical Field

[0001] This invention belongs to the field of soil improvement technology, specifically relating to a geniposide granule for soil remediation and its preparation method. Background Technology

[0002] With the rapid advancement of industrialization, urbanization, and intensive agriculture, soil heavy metal pollution has become an increasingly prominent problem. Heavy metals such as cadmium, lead, and zinc are easily accumulated in soil and difficult to degrade, posing a threat to human health through the food chain. They have become a significant factor restricting the safe use of arable land and the sustainable development of the ecological environment. Passivation remediation has become the mainstream technology for the treatment of heavy metal-contaminated farmland due to its simple operation, moderate cost, and lack of damage to soil structure. Currently, commonly used passivation materials include lime, dolomite, phosphates, biochar, and organic fertilizers.

[0003] However, existing passivation materials and technologies have significant limitations: single lime-based materials only adjust soil pH and have weak complexation and fixation capabilities for heavy metals, easily leading to soil compaction with long-term use; conventional biochar has a limited specific surface area and a single surface functional group, resulting in low adsorption capacity, and even after modification with a single acid-base or nitrogen source, its selectivity and stability for heavy metals remain insufficient; while phosphates can fix heavy metals through precipitation, they suffer from problems such as rapid nutrient release, easy leaching and loss, and poor compatibility with soil, making it difficult to simultaneously achieve passivation and soil fertility improvement. Furthermore, most remediation materials have limited functions, only achieving heavy metal passivation and failing to simultaneously improve soil organic matter content, enhance soil enzyme activity, and increase microbial activity, thus failing to meet the comprehensive needs for safe utilization of arable land.

[0004] In recent years, the application of natural active substances in soil remediation has gradually attracted attention. However, iridoid glycosides such as geniposide are easily degraded in the soil environment and have a short duration of action, lacking stable loading and slow-release technologies. There are few studies on the preparation of granules by combining natural active substances with modified biochar and phosphates, and there are problems such as poor granulation, easy disintegration of active ingredients, and insufficient process controllability.

[0005] Furthermore, existing soil remediation granules generally suffer from poor component compatibility, unclear synergistic mechanisms, low heavy metal removal rates, and poor long-term effectiveness, failing to achieve integrated remediation of "efficient passivation + fertility enhancement + soil health improvement." Therefore, developing a composite granule with stable loading, excellent heavy metal passivation effect, and the ability to simultaneously enhance soil organic matter and enzyme activity, along with its controllable preparation process, is of significant practical importance for promoting the safe and efficient remediation of heavy metal-contaminated soils. Summary of the Invention

[0006] The purpose of this invention is to provide a geniposide granule for soil remediation and its preparation method. The geniposide granule for soil remediation has a good effect on removing heavy metal ions and has a good promoting effect on organic matter content and enzyme activity.

[0007] The technical solution adopted by the present invention to achieve the above objectives is as follows: A method for preparing geniposide granules for soil remediation, comprising: Step 1: Add sodium humate and polyglutamic acid to deionized water, stir and mix at 45-50℃ for 25-30 minutes, then cool to room temperature, add geniposide, stir and disperse evenly to obtain micro-encapsulated geniposide colloidal solution. Step 2: Pre-treat the dolomite powder and composite phosphate separately, and then add them together with the modified biochar into a mixer and stir at room temperature for 10-20 minutes to obtain the repair base powder. Step 3: While stirring, slowly add the micro-encapsulated geniposide colloidal solution to the repair substrate powder. After the addition is complete, granulate the mixture using a granulator. Step 4: Gradual drying until the moisture content is ≤8%, cooling to room temperature, sieving, and obtaining geniposide granules for soil remediation.

[0008] The geniposide used in this invention is a natural active substance of the iridoid glycoside class, with a molecular structure rich in electron-rich active groups such as hydroxyl, carboxyl, and ether bonds, which can react with Cd in the soil. 2+ Pb 2+ Zn 2+ Gardenin undergoes complexation and chelation reactions with heavy metal ions to form stable cyclic complexes, reducing the migration capacity and bioavailability of heavy metal ions and achieving efficient passivation and fixation. Simultaneously, gardenin acts as a natural antioxidant, mitigating oxidative damage to soil enzyme protein structures caused by heavy metals, maintaining enzyme spatial conformation and catalytic activity, significantly enhancing the activity of key soil enzymes such as sucrase, and promoting soil nutrient cycling. Gardenin also provides high-quality carbon sources and energy substrates for soil microorganisms, accelerating the decomposition and humification of organic materials and increasing soil organic matter content. Protected by a microencapsulated colloidal system formed by sodium humate and polyglutamic acid, gardenin avoids rapid degradation by soil microorganisms, achieving slow and continuous release, extending its action period, and synergistically enhancing the comprehensive remediation effects of heavy metal passivation, soil fertility improvement, and enzyme activity enhancement.

[0009] Specifically, the preparation method of the above-mentioned geniposide granules for soil remediation includes the following steps: Step 1: Add sodium humate and polyglutamic acid to deionized water and stir at 60-150 r / min for 25-30 min at 45-50℃. Then cool to room temperature, add geniposide and stir at 60-80 r / min for 15-20 min (ensure the temperature does not exceed 30℃ during stirring) to obtain micro-encapsulated geniposide colloidal solution. Step 2: Grind the dolomite powder and pass it through an 80-100 mesh sieve to obtain pretreated dolomite powder for later use; crush the composite phosphate and pass it through a 60-80 mesh sieve to obtain pretreated composite phosphate for later use; then add the pretreated dolomite powder, pretreated composite phosphate and modified biochar together into a mixer and stir at room temperature for 10-20 minutes to obtain the repair base powder. Step 3: While stirring, slowly add the micro-encapsulated geniposide colloidal solution to the repair base powder. After the addition is complete, granulate using a disc granulator, adjusting the disc tilt angle to 45-50° and the rotation speed to 30-35 r / min. Step 4: Dry at 40-45℃ for 3-5 hours to set the shape and prevent disintegration; then dry at 55-60℃ until the moisture content is ≤8%, cool to room temperature, and sieve to obtain geniposide granules for soil remediation.

[0010] In this invention, in step one above, the mass ratio of sodium humate to polyglutamic acid is 1:0.15-0.2; the mass-volume ratio of sodium humate to deionized water is 1g:4-6mL; and the mass ratio of sodium humate to geniposide is 1:0.2-0.25.

[0011] For the present invention, in step two above, the mass ratio of dolomite powder to modified biochar is 1:1.5-2; the mass ratio of dolomite powder to composite phosphate is 1:0.3-0.6.

[0012] For the purposes of this invention, in step three above, the mass ratio of the repair substrate powder to the micro-embedded geniposide colloidal solution is 1:0.4-0.6.

[0013] For the purposes of this invention, the aforementioned composite phosphate comprises: calcium dihydrogen phosphate, diammonium hydrogen phosphate, and sodium tripolyphosphate; the order of addition is: first add sodium tripolyphosphate, then add diammonium hydrogen phosphate, and finally add calcium dihydrogen phosphate, to avoid premature hydrolysis due to prolonged direct contact between acidic salts and polyphosphates.

[0014] For the purposes of this invention, the mass ratio of the above-mentioned calcium dihydrogen phosphate, diammonium hydrogen phosphate and sodium tripolyphosphate is 1:0.4-0.6:0.15-0.2.

[0015] This invention employs a ternary composite of calcium dihydrogen phosphate, diammonium hydrogen phosphate, and sodium tripolyphosphate to achieve a triple synergistic effect of rapid fertilization, long-term passivation, and complexation and fixation. Calcium dihydrogen phosphate is used for slow-release calcium and phosphorus, adjusting soil pH, and forming insoluble phosphate precipitates with heavy metals to passivate Cd, Pb, and Zn. Diammonium hydrogen phosphate provides rapid nitrogen and phosphorus, replenishing nutrients, promoting microbial activity, and improving soil fertility. Sodium tripolyphosphate is used to complex heavy metal ions, enhancing passivation stability, and also plays a role in binding and granulation. Furthermore, the ternary composite of calcium dihydrogen phosphate, diammonium hydrogen phosphate, and sodium tripolyphosphate has good compatibility with biochar and dolomite.

[0016] For the purposes of this invention, the particle size of the geniposide granules for soil remediation prepared in step four above is 2-4 mm.

[0017] The present invention also discloses a method for preparing modified biochar, comprising: adding bamboo powder to deionized water, hydrothermally reacting at 200-215℃ for 20-28h, cooling to room temperature, filtering to obtain hydrothermal char; then adding the hydrothermal char to potassium hydroxide solution, soaking at room temperature for 20-30h, filtering, drying, and then adding it to a mixture of urea and 2-tolylthioformamide, grinding evenly, pyrolyzing at 750-850℃ for 1-2h under a nitrogen atmosphere, cooling to room temperature, washing successively with hydrochloric acid solution, washing with deionized water, and drying to obtain modified biochar.

[0018] This invention employs hydrothermal carbonization and potassium hydroxide activation for synergistic modification with nitrogen and sulfur dual doping to prepare biochar. First, a basic carbon framework is constructed via a hydrothermal reaction, followed by potassium hydroxide impregnation and etching to form hierarchical channels, significantly increasing the specific surface area and pore structure, and enhancing the physical adsorption of heavy metal ions. Subsequently, using urea as the nitrogen source and 2-tolylthioformamide as the sulfur source, N and S dual-element co-doping is achieved under a high-temperature nitrogen atmosphere, introducing amide groups, C=S, and other active sites onto the carbon surface. The sulfur-containing groups are typical soft base ligands that can react with Cd. 2+ Pb 2+ The formation of strong coordination bonds between heavy metals and soft acids significantly enhances the complexation stability. Nitrogen-doped groups increase surface polarity and hydrophilicity, enhancing the adsorption selectivity for heavy metals and nutrient ions. This modified biochar combines physical adsorption, chemical complexation, and ion exchange, efficiently immobilizing heavy metals while improving soil aggregate structure, water and fertilizer retention, and providing a habitat for microorganisms, thus synergistically improving soil remediation and fertility enhancement.

[0019] Specifically, the preparation method of the above-mentioned modified biochar includes the following steps: Bamboo powder is rinsed 3-5 times with deionized water to remove impurities and particles from its surface. It is then dried at 55-65℃. The bamboo powder is then added to deionized water (mass-volume ratio of bamboo powder to deionized water: 1g:8-15mL), stirred until evenly dispersed, and subjected to a hydrothermal reaction at 200-215℃ for 20-28 hours. After cooling to room temperature, it is filtered to obtain hydrothermal char. The hydrothermal char is then added to a 65-70g / L potassium hydroxide solution and impregnated at room temperature for 20-30 hours, followed by filtration. Vacuum dried, then added to a mixture of urea and 2-tolylthioformamide, ground evenly, and then heated to 750-850℃ at a rate of 8-10℃ / min under a nitrogen atmosphere (nitrogen flow rate of 45-55 mL / min) for 1-2 h. After cooling to room temperature, it was washed 3-5 times with a 0.3-0.6 mol / L hydrochloric acid solution and 3-5 times with deionized water, and then dried to constant weight at 50-65℃ to obtain modified biochar.

[0020] For the purposes of this invention, the mass-to-volume ratio of the hydrothermal char to the potassium hydroxide solution is 1g:40-50mL; the mass ratio of the hydrothermal char to urea is 1:0.4-0.6; and the mass ratio of urea to 2-tolylthiocarboxamide is 1:0.2-0.5.

[0021] The beneficial effects of this invention include: This invention provides a geniposide granule for soil remediation and its preparation method. The method involves micro-encapsulating geniposide with sodium humate and polyglutamic acid, then mixing and granulating it with urea and 2-tolylthioformamide-modified biochar, dolomite powder, and composite phosphate to prepare the geniposide granule for soil remediation. The active groups such as hydroxyl and carboxyl groups in geniposide complex heavy metals, protect soil enzymes, and promote organic matter accumulation. The urea and 2-tolylthioformamide-modified biochar achieves nitrogen and sulfur dual doping and a hierarchical porous structure, significantly enhancing adsorption and complexation capabilities. The ternary composite phosphate provides synergistic effects of precipitation passivation, nutrient supply, and complexation stabilization. Sodium humate and polyglutamic acid micro-encapsulate and slowly release geniposide, combined with gradient granulation and drying, to obtain a stable granule with high heavy metal removal rate, increased organic matter, and enhanced enzyme activity.

[0022] Therefore, the present invention provides a geniposide granule for soil remediation and its preparation method. The geniposide granule for soil remediation has a good effect on removing heavy metal ions and has a good promoting effect on organic matter content and enzyme activity. Attached Figure Description

[0023] Figure 1 The results show the test effects of the soil remediation granules prepared in Examples 1-3 and Comparative Examples 1-4 on the removal of heavy metal ions. Figure 2 The test results show the effect of the soil remediation granules prepared in Examples 1-3 and Comparative Examples 1-4 on the organic matter content. Figure 3 The results show the effects of the soil remediation granules prepared in Examples 1-3 and Comparative Examples 1-4 on enzyme activity. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions of the present invention will be further described in detail below with reference to specific embodiments: Example 1: A method for preparing geniposide granules for soil remediation includes the following steps: Step 1: Add sodium humate and polyglutamic acid to deionized water and stir at 60 r / min for 30 min at 45℃. Then cool to room temperature, add geniposide and stir at 60 r / min for 20 min (ensure the temperature does not exceed 30℃ during stirring) to obtain micro-embedded geniposide colloidal solution. Step 2: Grind the dolomite powder and pass it through an 80-mesh sieve to obtain pretreated dolomite powder for later use. Crush the composite phosphate (composite phosphate includes: calcium dihydrogen phosphate, diammonium hydrogen phosphate, and sodium tripolyphosphate; the order of addition is: first add sodium tripolyphosphate, then add diammonium hydrogen phosphate, and finally add calcium dihydrogen phosphate; the mass ratio of calcium dihydrogen phosphate, diammonium hydrogen phosphate, and sodium tripolyphosphate is 1:0.4:0.15) and pass it through a 60-mesh sieve to obtain pretreated composite phosphate for later use. Then, add the pretreated dolomite powder, pretreated composite phosphate, and modified biochar together into a mixer and stir at room temperature for 10 minutes to obtain the repair substrate powder. Step 3: While stirring, slowly add the micro-encapsulated geniposide colloidal solution to the repair base powder. After the addition is complete, granulate using a disc granulator, adjusting the disc tilt angle to 45° and the rotation speed to 35 r / min. Step 4: Dry at 40℃ for 5 hours to set and prevent disintegration; then dry at 55℃ until the moisture content is ≤8%, cool to room temperature, and sieve to obtain soil remediation granules with a particle size of 2mm.

[0025] In step one, the mass ratio of sodium humate to polyglutamic acid is 1:0.15; the mass-to-volume ratio of sodium humate to deionized water is 1g:4mL; and the mass ratio of sodium humate to geniposide is 1:0.2. In step two, the mass ratio of dolomite powder to modified biochar is 1:1.5; and the mass ratio of dolomite powder to composite phosphate is 1:0.3. In step three, the mass ratio of the repair substrate powder to the micro-embedded geniposide colloidal solution is 1:0.4.

[0026] The method for preparing modified biochar includes the following steps: Bamboo powder was rinsed three times with deionized water to remove impurities and particles from its surface. It was then dried at 55°C. The bamboo powder was then added to deionized water (mass-volume ratio of bamboo powder to deionized water: 1 g: 8 mL), stirred until evenly dispersed, and subjected to hydrothermal reaction at 200°C for 28 h. After cooling to room temperature, the mixture was filtered to obtain hydrothermal char. The hydrothermal char was then added to a 65 g / L potassium hydroxide solution and impregnated at room temperature for 30 h. After filtration and vacuum drying, it was added to a mixture of urea and 2-tolylthioformamide, ground evenly, and then heated to 750°C at a rate of 8°C / min under a nitrogen atmosphere (nitrogen flow rate of 45 mL / min) for 2 h. After cooling to room temperature, it was washed three times with 0.3 mol / L hydrochloric acid solution and three times with deionized water, and then dried at 50°C to constant weight to obtain modified biochar.

[0027] The mass-to-volume ratio of hydrothermal charcoal to potassium hydroxide solution was 1 g: 40 mL; the mass ratio of hydrothermal charcoal to urea was 1: 0.4; and the mass ratio of urea to 2-tolylthiocarboxamide was 1: 0.2.

[0028] Example 2: A method for preparing geniposide granules for soil remediation includes the following steps: Step 1: Add sodium humate and polyglutamic acid to deionized water. Stir and mix at 150 r / min for 25 min at 50℃. Then cool to room temperature, add geniposide, and stir and disperse at 80 r / min for 15 min (ensure the temperature does not exceed 30℃ during stirring) to obtain micro-embedded geniposide colloidal solution. Step 2: Grind the dolomite powder and pass it through a 100-mesh sieve to obtain pretreated dolomite powder for later use. Crush the composite phosphate (composite phosphate includes: calcium dihydrogen phosphate, diammonium hydrogen phosphate, and sodium tripolyphosphate; the order of addition is: first add sodium tripolyphosphate, then add diammonium hydrogen phosphate, and finally add calcium dihydrogen phosphate; the mass ratio of calcium dihydrogen phosphate, diammonium hydrogen phosphate, and sodium tripolyphosphate is 1:0.6:0.2) and pass it through an 80-mesh sieve to obtain pretreated composite phosphate for later use. Then, add the pretreated dolomite powder, pretreated composite phosphate, and modified biochar together into a mixer and stir at room temperature for 20 minutes to obtain the repair substrate powder. Step 3: While stirring, slowly add the micro-embedded geniposide colloidal solution to the repair base powder. After the addition is complete, granulate using a disc granulator, adjusting the disc tilt angle to 50° and the rotation speed to 35 r / min. Step 4: Dry at 45℃ for 3 hours to set and prevent disintegration; then dry at 60℃ until the moisture content is ≤8%, cool to room temperature, and sieve to obtain soil remediation granules with a particle size of 4mm.

[0029] In step one, the mass ratio of sodium humate to polyglutamic acid is 1:0.2; the mass-to-volume ratio of sodium humate to deionized water is 1g:6mL; and the mass ratio of sodium humate to geniposide is 1:0.25. In step two, the mass ratio of dolomite powder to modified biochar is 1:2; and the mass ratio of dolomite powder to composite phosphate is 1:0.6. In step three, the mass ratio of the repair substrate powder to the micro-embedded geniposide colloidal solution is 1:0.6.

[0030] The method for preparing modified biochar includes the following steps: Bamboo powder was rinsed five times with deionized water to remove impurities and particles from its surface. It was then dried at 65°C. The bamboo powder was then added to deionized water (mass-volume ratio of bamboo powder to deionized water: 1g:15mL), stirred until evenly dispersed, and subjected to hydrothermal reaction at 215°C for 20 hours. After cooling to room temperature, the mixture was filtered to obtain hydrothermal char. The hydrothermal char was then added to a 70g / L potassium hydroxide solution and impregnated at room temperature for 20 hours. After filtration and vacuum drying, it was added to a mixture of urea and 2-tolylthioformamide, ground evenly, and then heated to 850°C at a rate of 10°C / min under a nitrogen atmosphere (nitrogen flow rate of 55mL / min) for 1 hour. After cooling to room temperature, the mixture was washed five times with 0.6mol / L hydrochloric acid solution and five times with deionized water. Finally, it was dried at 65°C to constant weight to obtain modified biochar.

[0031] The mass-to-volume ratio of hydrothermal charcoal to potassium hydroxide solution was 1 g: 40 mL; the mass ratio of hydrothermal charcoal to urea was 1: 0.4; and the mass ratio of urea to 2-tolylthiocarboxamide was 1: 0.5.

[0032] Example 3: A method for preparing geniposide granules for soil remediation includes the following steps: Step 1: Add sodium humate and polyglutamic acid to deionized water and stir at 80 r / min for 28 min at 48℃. Then, cool to room temperature, add geniposide, and stir at 70 r / min for 18 min (ensure the temperature does not exceed 30℃ during stirring) to obtain micro-embedded geniposide colloidal solution. Step 2: Grind the dolomite powder and pass it through a 100-mesh sieve to obtain pretreated dolomite powder for later use. Crush the composite phosphate (composite phosphate includes: calcium dihydrogen phosphate, diammonium hydrogen phosphate, and sodium tripolyphosphate; the order of addition is: first add sodium tripolyphosphate, then add diammonium hydrogen phosphate, and finally add calcium dihydrogen phosphate; the mass ratio of calcium dihydrogen phosphate, diammonium hydrogen phosphate, and sodium tripolyphosphate is 1:0.5:0.18) and pass it through an 80-mesh sieve to obtain pretreated composite phosphate for later use. Then, add the pretreated dolomite powder, pretreated composite phosphate, and modified biochar together into a mixer and stir at room temperature for 15 minutes to obtain the repair substrate powder. Step 3: While stirring, slowly add the micro-embedded geniposide colloidal solution to the repair base powder. After the addition is complete, granulate using a disc granulator, adjusting the disc tilt angle to 48° and the rotation speed to 33 r / min. Step 4: Dry at 42℃ for 4 hours to set and prevent disintegration; then dry at 58℃ until the moisture content is ≤8%, cool to room temperature, and sieve to obtain soil remediation granules with a particle size of 3mm.

[0033] In step one, the mass ratio of sodium humate to polyglutamic acid is 1:0.18; the mass-to-volume ratio of sodium humate to deionized water is 1g:5mL; and the mass ratio of sodium humate to geniposide is 1:0.23. In step two, the mass ratio of dolomite powder to modified biochar is 1:1.7; and the mass ratio of dolomite powder to composite phosphate is 1:0.5. In step three, the mass ratio of the repair substrate powder to the micro-embedded geniposide colloidal solution is 1:0.5.

[0034] The method for preparing modified biochar includes the following steps: Bamboo powder was rinsed four times with deionized water to remove impurities and particles from its surface. It was then dried at 60°C. The bamboo powder was then added to deionized water (mass-volume ratio of bamboo powder to deionized water: 1 g: 10 mL), stirred until evenly dispersed, and subjected to hydrothermal reaction at 210°C for 27 h. After cooling to room temperature, the mixture was filtered to obtain hydrothermal char. The hydrothermal char was then added to a 68 g / L potassium hydroxide solution and impregnated at room temperature for 24 h. After filtration and vacuum drying, the char was added to a mixture of urea and 2-tolylthioformamide, ground evenly, and then heated to 800°C at a rate of 9°C / min under a nitrogen atmosphere (nitrogen flow rate of 50 mL / min) for 1.5 h. After cooling to room temperature, the char was washed four times with 0.5 mol / L hydrochloric acid solution and four times with deionized water. Finally, it was dried at 60°C to constant weight to obtain modified biochar.

[0035] The mass-to-volume ratio of hydrothermal charcoal to potassium hydroxide solution was 1 g: 45 mL; the mass ratio of hydrothermal charcoal to urea was 1: 0.5; and the mass ratio of urea to 2-tolylthiocarboxamide was 1: 0.3.

[0036] Comparative Example 1: The difference between the preparation method of a soil remediation granule and Example 1 is that biochar is used instead of modified biochar.

[0037] The method for preparing biochar includes the following steps: Bamboo powder was rinsed four times with deionized water to remove impurities and particles from its surface. It was then dried at 60℃. The bamboo powder was then added to deionized water (mass-volume ratio of bamboo powder to deionized water: 1g:10mL), stirred until evenly dispersed, and subjected to hydrothermal reaction at 210℃ for 27 hours. After cooling to room temperature, the mixture was filtered to obtain hydrothermal char. The hydrothermal char was then added to a 68g / L potassium hydroxide solution and impregnated at room temperature for 24 hours. After filtration and vacuum drying, it was ground and then pyrolyzed at 800℃ for 1.5 hours under a nitrogen atmosphere (nitrogen flow rate of 50mL / min) at a heating rate of 9℃ / min. After cooling to room temperature, it was washed four times with 0.5mol / L hydrochloric acid solution and four times with deionized water. Finally, it was dried at 60℃ to constant weight to obtain modified biochar.

[0038] The mass-to-volume ratio of hydrothermal charcoal to potassium hydroxide solution is 1 g: 45 mL.

[0039] Comparative Example 2: The difference between this method for preparing soil remediation granules and Example 1 is that geniposide is not added.

[0040] Comparative Example 3: The difference between a method for preparing soil remediation granules and Comparative Example 2 is that biochar is used instead of modified biochar.

[0041] The preparation method of biochar is the same as that of Comparative Example 1.

[0042] Comparative Example 4: The difference between the preparation method of a soil remediation granule and Comparative Example 2 is that the preparation method of the modified biochar is different.

[0043] The difference between the preparation method of modified biochar and Comparative Example 2 is that 2-tolylthiocarbamate is not added.

[0044] Test case 1. Heavy metal ion removal effect test 700g of heavy metal contaminated soil (Cd in the heavy metal contaminated soil) were respectively... 2+ The content is 1.85 mg / kg, Pb 2+The content is 274 mg / kg, Zn 2+ A soil remediation granule sample (containing 651 mg / kg) was added to a 1000 mL flowerpot with a perforated bottom and a small tray. Then, 15 g of the sample was added to each pot. Three replicates were set up for each group. No soil remediation granules were added to the control group. The soil was incubated at 25℃ in a constant temperature incubator, and the soil moisture was maintained at 60% of field capacity by spraying deionized water. After 30 days of incubation, 2 g of soil sample was placed in a centrifuge tube, and 16 mL of 0.1 mol / L calcium chloride solution was added. The mixture was then shaken at 180 rpm for 1 hour. After centrifugation, filtration, and collection of the test solution, the concentration of heavy metal ions in the test solution was measured using flame atomic absorption spectrometry, and the heavy metal ion removal rate was calculated using the following formula: W / %=[(S0-S1) / S0]×100% Where W is the heavy metal ion removal rate (%), S0 is the heavy metal ion concentration in the soil before treatment (mg / kg), and S1 is the heavy metal ion concentration in the soil after treatment (mg / kg).

[0045] The above tests were performed on the blank group, and the heavy metal ion removal rate of the blank group was measured to be 7.6%. The above tests were also performed on the soil remediation granules prepared in Examples 1-3 and Comparative Examples 1-4, and the results are as follows: Figure 1 As shown. By Figure 1 It can be seen that the removal rates of heavy metal ions in Examples 1-3 and Comparative Examples 1-4 were significantly improved compared to the blank group; the removal rates of heavy metal ions in Example 1 were improved compared to Comparative Example 2, and the removal rates of heavy metal ions in Comparative Example 1 were improved compared to Comparative Example 3. This indicates that the addition of geniposide enabled the prepared soil remediation granules to have a good effect on the removal of heavy metal ions. This may be because geniposide is a natural active substance of iridoid glycosides, and its molecular structure is rich in electron-rich active groups such as hydroxyl, carboxyl, and ether bonds, which can react with Cd in the soil. 2+ Pb 2+ Zn 2+ When heavy metal ions undergo complexation and chelation reactions to form stable cyclic complexes, the migration ability and bioavailability of heavy metal ions are reduced, achieving efficient passivation and fixation. Compared with Comparative Example 1 and Comparative Example 2, the removal rate of heavy metal ions in Example 1 is significantly increased. This indicates that the use of urea and 2-tolylthioformamide to modify biochar, and then using the modified biochar in the preparation of soil remediation granules, results in soil remediation granules with good heavy metal ion removal effects. This may be because the present invention uses urea as a nitrogen source and 2-tolylthioformamide as a sulfur source, achieving N and S dual-element co-doping under a high-temperature nitrogen atmosphere, introducing amide groups, C=S and other active sites on the carbon surface. Among them, the sulfur-containing groups are typical soft base ligands that can react with Cd. 2+ Pb2+ The formation of strong coordination bonds between heavy metals and soft acids can significantly enhance the complexation stability. Compared with Comparative Example 4, Comparative Example 2 also showed an increase in the removal rate of heavy metal ions, indicating that the addition of 2-tolylthioformamide during the preparation of modified biochar, followed by the use of the modified biochar in the preparation of soil remediation granules, has a good promoting effect on the removal of heavy metal ions.

[0046] 2. Effect of Organic Matter Content on Performance Testing After culturing heavy metal-contaminated soil for 30 days using the cultivation method described in Example 1, the organic matter content before and after soil cultivation was determined using the potassium dichromate dilution thermochromic method. The formula for calculating the organic matter content growth rate is as follows: G / %=[(Q1-Q0) / Q0]×100% Where G is the organic matter content growth rate, %; Q0 is the organic matter content in the soil before treatment, %; Q1 is the organic matter content in the soil after treatment, %.

[0047] The above tests were performed on the blank group, and the organic matter content growth rate of the blank group was measured to be 1.59%. The above tests were also performed on the soil remediation granules prepared in Examples 1-3 and Comparative Examples 1-4, and the results are as follows: Figure 2 As shown. By Figure 2 It can be seen that the organic matter content growth rate of Examples 1-3 and Comparative Examples 1-4 was significantly increased compared with the blank group; the organic matter content growth rate of Example 1 compared with Comparative Example 2 and Comparative Example 1 compared with Comparative Example 3 was also increased. This indicates that the addition of geniposide resulted in a good organic matter content growth effect in the prepared soil remediation granules. This may be because geniposide can also provide high-quality carbon sources and energy substrates for soil microorganisms, promote microbial proliferation and metabolic activities, accelerate the decomposition and humification of organic materials, and increase the soil organic matter content. Compared to Comparative Example 3, the growth rate of organic matter content increased significantly, indicating that using urea and 2-tolylthioformamide to modify biochar, and then using the modified biochar in the preparation of soil remediation granules, resulted in soil remediation granules with a good organic matter content growth effect. Compared to Comparative Example 4, Comparative Example 2 also showed an increased organic matter content growth rate, indicating that adding 2-tolylthioformamide during the preparation of modified biochar, and then using the modified biochar in the preparation of soil remediation granules, resulted in soil remediation granules with a good promoting effect on organic matter content growth.

[0048] 3. Test on the effect of enzyme activity on efficacy After culturing heavy metal-contaminated soil for 30 days using the cultivation method described in Example 1, sucrase activity was determined using the 3,5-dinitrosalicylic acid colorimetric method. The formula for calculating the sucrase activity growth rate is as follows: N / %=[(R1-R0) / R0]×100% Where N is the sucrase activity growth rate (%), and R0 is the sucrase activity in the soil before treatment (mg / g). -1 ·d -1 R1 represents the sucrase activity in the treated soil, in mg / g. -1 ·d -1 .

[0049] The above tests were performed on the blank group, and the sucrase activity growth rate of the blank group was measured to be 1.21%. The above tests were also performed on the soil remediation granules prepared in Examples 1-3 and Comparative Examples 1-4, and the results are as follows: Figure 3 As shown. By Figure 3 It can be seen that the growth rate of sucrase activity in Examples 1-3 and Comparative Examples 1-4 was significantly increased compared to the blank group; the growth rate of sucrase activity was also increased in Example 1 compared to Comparative Example 2 and in Comparative Example 1 compared to Comparative Example 3. This indicates that the addition of geniposide resulted in a good sucrase activity growth effect in the prepared soil remediation granules. This may be because geniposide can act as a natural antioxidant, which can reduce the oxidative damage of heavy metals to the soil enzyme protein structure, maintain the spatial conformation and catalytic activity of enzymes, significantly improve the activity of key soil enzymes such as sucrase, and promote soil nutrient cycling. 1. Compared with Comparative Example 3, Comparative Example 2 showed a significantly increased growth rate of sucrase activity. This indicates that using urea and 2-tolylthioformamide to modify biochar, and then using the modified biochar in the preparation of soil remediation granules, resulted in soil remediation granules with a good sucrase activity growth effect. Compared with Comparative Example 4, Comparative Example 2 also showed an increased growth rate of sucrase activity, indicating that adding 2-tolylthioformamide during the preparation of modified biochar, and then using the modified biochar in the preparation of soil remediation granules, resulted in soil remediation granules with a good promoting effect on sucrase activity growth.

[0050] The conventional techniques described in the above embodiments are existing technologies known to those skilled in the art, and therefore will not be described in detail here.

[0051] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing geniposide granules for soil remediation, characterized in that, include: Step 1: Add sodium humate and polyglutamic acid to deionized water, stir and mix at 45-50℃ for 25-30 minutes, then cool to room temperature, add geniposide, stir and disperse evenly to obtain micro-encapsulated geniposide colloidal solution. Step 2: Pre-treat the dolomite powder and composite phosphate separately, and then add them together with the modified biochar into a mixer and stir at room temperature for 10-20 minutes to obtain the repair substrate powder. Step 3: While stirring, slowly add the micro-encapsulated geniposide colloidal solution to the repair substrate powder. After the addition is complete, granulate the mixture using a granulator. Step 4: Gradient drying until the moisture content is ≤8%, cooling to room temperature, sieving, and obtaining geniposide granules for soil remediation; The method for preparing the modified biochar includes: adding bamboo powder to deionized water, hydrothermally reacting at 200-215℃ for 20-28h, cooling to room temperature, filtering, and obtaining hydrothermal char; then adding the hydrothermal char to potassium hydroxide solution, soaking at room temperature for 20-30h, filtering, drying, and then adding it to a mixture of urea and 2-tolylthioformamide, grinding evenly, pyrolyzing at 750-850℃ for 1-2h under a nitrogen atmosphere, cooling to room temperature, washing successively with hydrochloric acid solution, washing with deionized water, and drying to obtain modified biochar.

2. The method for preparing geniposide granules for soil remediation according to claim 1, characterized in that: In step one, the mass ratio of sodium humate to polyglutamic acid is 1:0.15-0.2; the mass-volume ratio of sodium humate to deionized water is 1g:4-6mL; and the mass ratio of sodium humate to geniposide is 1:0.2-0.

25.

3. The method for preparing geniposide granules for soil remediation according to claim 1, characterized in that: In step two, the specific steps for pretreating dolomite powder and composite phosphate are as follows: grind the dolomite powder and pass it through an 80-100 mesh sieve for later use; crush the composite phosphate and pass it through a 60-80 mesh sieve for later use.

4. The method for preparing geniposide granules for soil remediation according to claim 1, characterized in that: In step two, the mass ratio of dolomite powder to modified biochar is 1:1.5-2; the mass ratio of dolomite powder to composite phosphate is 1:0.3-0.

6.

5. The method for preparing geniposide granules for soil remediation according to claim 1, characterized in that: In step three, the mass ratio of the repair substrate powder to the micro-embedded geniposide colloidal solution is 1:0.4-0.

6.

6. The method for preparing geniposide granules for soil remediation according to claim 1, characterized in that: The composite phosphate comprises: calcium dihydrogen phosphate, diammonium hydrogen phosphate, and sodium tripolyphosphate; the mass ratio of calcium dihydrogen phosphate, diammonium hydrogen phosphate, and sodium tripolyphosphate is 1:0.4-0.6:0.15-0.

2.

7. The method for preparing geniposide granules for soil remediation according to claim 1, characterized in that: In step four, the specific drying steps of gradient drying are as follows: dry at 40-45℃ for 3-5 hours to set the shape and prevent disintegration; then dry at 55-60℃ until the moisture content is ≤8%.

8. The method for preparing geniposide granules for soil remediation according to claim 1, characterized in that: The geniposide granules prepared in step four for soil remediation have a particle size of 2-4 mm.

9. The method for preparing geniposide granules for soil remediation according to claim 1, characterized in that: The mass-to-volume ratio of the hydrothermal char to the potassium hydroxide solution is 1 g: 40-50 mL; the mass ratio of the hydrothermal char to urea is 1: 0.4-0.6; and the mass ratio of urea to 2-tolylthioformamide is 1: 0.2-0.5.

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