Soil conditioner for heavy metal contaminated soil and preparation process thereof

Abstract

The invention provides a soil conditioner for heavy metal contaminated soil and a preparation process of the soil conditioner, and belongs to the technical field of soil remediation. The preparation process comprises the following steps: preparing Fe3O4 (at) ZnO; preparation of sulfonated humic acid-chitosan coated Fe3O4 (at) ZnO; preparing matured compost; and preparing the soil conditioner. The sulfonated humic acid-chitosan coated Fe3O4 (at) ZnO, the matured compost and the oyster shells are mixed with one another, so that the air permeability and the water permeability of the soil can be improved, the water and fertilizer retention capacity of the soil can be enhanced, heavy metals can be adsorbed and fixed by the sulfonated humic acid-chitosan coated Fe3O4 (at) ZnO, the bioavailability of the heavy metals can be reduced, and the soil fertility can be improved. The risk of migrating into the plant body is reduced, the quality safety of agricultural products is guaranteed, and meanwhile, the remediation and improvement of the soil environment are also facilitated.

Description

Technical Field

[0001] The present invention relates to the technical field of soil remediation, and in particular to a soil conditioner for heavy metal contaminated soil and a preparation process thereof. Background Art

[0002] Against the backdrop of today's rapidly advancing industrialization and urbanization, heavy metal contamination in soil has become a globally recognized environmental challenge. With the large-scale development of various industrial activities, such as metal smelting, electroplating, and chemical production, large amounts of improperly treated heavy metal-containing waste are being released into the surrounding environment. During mining, the disorderly accumulation of waste slag and tailings causes heavy metals such as lead, cadmium, mercury, copper, and zinc to continuously migrate into the soil environment. Furthermore, long-standing irrational fertilization and pesticide application practices in agriculture, such as the excessive use of heavy metal-containing phosphate fertilizers and some heavy metal-containing pesticides, have also exacerbated the accumulation of heavy metals in the soil.

[0003] Once heavy metals enter the soil, they alter its physical and chemical properties. On the one hand, they disrupt the charge balance of soil colloids, destroying the structure of soil aggregates and reducing soil aeration and water permeability, which in turn affects normal respiration and water and nutrient absorption by plant roots. On the other hand, heavy metals chemically react with organic matter and minerals in the soil, reducing the content of available nutrients and dramatically reducing soil fertility. Once-fertile farmland gradually becomes barren, hindering crop growth, leading to declining yields and even the possibility of crop failure.

[0004] Most soil conditioners currently available on the market suffer from a single function. Some focus on regulating soil pH or improving soil structure, but neglect the treatment of heavy metal pollution, failing to effectively reduce the biotoxicity of heavy metals. Furthermore, most existing soil conditioners are organic, and due to their single adsorption mechanism, they cannot effectively remove pollutants from the soil. Instead, they increase costs due to increased input. Furthermore, since organic matter completely degrades in the soil, adsorbed pollutants return to the soil as the carrier degrades. Therefore, existing soil conditioners only delay soil remediation and fail to effectively address the root cause of soil pollution.

[0005] Therefore, we proposed a soil conditioner for heavy metal contaminated soil and a preparation process thereof. Summary of the Invention

[0006] In view of the shortcomings of the prior art, the present invention aims to provide a soil conditioner for heavy metal contaminated soil and a preparation process thereof.

[0007] A preparation process of a soil conditioner for heavy metal contaminated soil comprises the following steps:

[0008] S1: Preparation of Fe3O4@ZnO

[0009] Zn(OAc)2·2H2O and sodium hydroxide were dissolved in deionized water, and then Fe3O4 nanoparticles were added to obtain a mixed solution. The mixed solution was transferred to a polytetrafluoroethylene liner and sealed. The temperature was then raised to react to prepare Fe3O4@ZnO.

[0010] S2: Preparation of sulfonated humic acid-chitosan coated Fe3O4@ZnO

[0011] Sulfonated humic acid aqueous solution and chitosan solution were prepared, Fe3O4@ZnO was dispersed in deionized water, and then the sulfonated humic acid aqueous solution, chitosan solution and glutaraldehyde were added to react to obtain sulfonated humic acid-chitosan coated Fe3O4@ZnO;

[0012] S3: Preparation of mature compost

[0013] Composting crop straw, livestock and poultry manure, fallen leaves and other organic waste;

[0014] S4: Preparation of soil conditioner

[0015] A soil conditioner is obtained by mixing 30-50 parts by weight of sulfonated humic acid-chitosan coated Fe3O4@ZnO, 20-30 parts by weight of decomposed compost and 5-8 parts by weight of oyster shells.

[0016] Furthermore, step S1: preparation of Fe3O4@ZnO specifically includes the following steps:

[0017] S1.1: Dissolve 10-12 parts by weight of FeCl3·6H2O, 80-90 parts by weight of sodium acetate, and 3-5 parts by weight of trisodium citrate in 110-120 parts by weight of ethylene glycol. Stir the mixture at 200-300 rpm for 20-30 minutes at room temperature, transfer the mixture to a sealed polytetrafluoroethylene-lined tube, and then heat the tube to 200-220°C and maintain the temperature for 12-14 hours. After the reaction is complete, magnetically collect the dark brown product using an external magnetic field, wash it, and vacuum dry it at 50-60°C for 10-12 hours to obtain Fe3O4 nanoparticles.

[0018] S1.2: Dissolve 20-30 parts by weight of Zn(OAc)2·2H2O and 40-50 parts by weight of sodium hydroxide in 80-100 parts by weight of deionized water, stir and mix at 200-230 rpm for 10-20 min, then add the Fe3O4 nanoparticles and ultrasonically disperse for 20-30 min to obtain a mixed solution;

[0019] S1.3: Transfer the mixed solution to a sealed polytetrafluoroethylene-lined tube, then heat to 160-180°C and maintain for 12-14 hours. When the reaction is complete, magnetically collect the dark brown product using an external magnetic field. After washing, vacuum dry it at 50-60°C for 10-12 hours to obtain Fe3O4@ZnO.

[0020] Furthermore, step S2: preparation of sulfonated humic acid-chitosan coated Fe3O4@ZnO specifically comprises the following steps:

[0021] S2.1: Add 10-12 parts by weight of humic acid to 10-12 parts by weight of a 15% volume fraction H2SO4 solution, stir to mix, and evenly spread the mixture in a Petri dish. Place the Petri dish in an oven and heat to 50-60°C for 3-4 hours. After the sulfonation reaction is complete, cool to room temperature to obtain sulfonated humic acid.

[0022] S2.2: Weigh 5-8 parts by weight of chitosan powder and dissolve it in 1-3% acetic acid solution. Stir at room temperature for 4-6 hours until the chitosan is completely dissolved to prepare a chitosan solution with a concentration of 5-10 g / L. Simultaneously, prepare a 10-20 g / L aqueous solution of sulfonated humic acid.

[0023] S2.3: Disperse 10-12 parts by weight of Fe3O4@ZnO in 30-50 parts by weight of deionized water, ultrasonically disperse for 40-50 minutes to obtain a Fe3O4@ZnO dispersion, then add 3-5 parts by weight of a sulfonated humic acid aqueous solution, and continue stirring at room temperature for 3-4 hours. Then, add 3-4 parts by weight of a chitosan solution and 0.5-0.8 parts by weight of 0.5-1% glutaraldehyde, and adjust the pH value of the solution to 5-6. Stir and react at 40-50°C for 3-5 hours. After the reaction, wash with deionized water 2-3 times, and separate using an external magnetic field to obtain sulfonated humic acid-chitosan-encapsulated Fe3O4@ZnO.

[0024] Furthermore, step S3: preparing mature compost, specifically comprises the following steps:

[0025] S3.1: Collect organic waste such as crop straw, livestock and poultry manure, and fallen leaves, and mix them in a ratio of 3:2:1-2 to obtain compost raw materials. Select an open area with high terrain, good drainage, and smooth ventilation. Lay a 20-30 cm thick layer of gravel on the ground, and then spread 10-15 cm of coarse sand on the gravel layer. Set up a fence around the site with a height of 1-1.5 m to obtain a composting site.

[0026] S3.2: Pile the mixed compost materials into a trapezoidal pile with a base width of 2-3m, a height of 1.5-2m, and a top width of 1-1.5m at the composting site. The weight of each pile should be controlled at 3-5 tons. In the early stages of composting, use a watering can to evenly spray the materials with clean water to a moisture content of 50-60%. Then, add 1-2% of a composite microbial agent.

[0027] S3.3: During the first 1-2 weeks of composting, the material temperature is monitored every day. When the temperature rises to 50-65℃, it enters the high-temperature decomposition period, which lasts for 3-4 weeks. During this period, the pile is turned over every 3-4 days. When the temperature gradually drops, it enters the post-decomposition period, which lasts for 2-3 weeks. The moisture content is maintained at 40-50%. After 3-6 months of complete decomposition process, mature compost is obtained.

[0028] Furthermore, the composite microbial agent in step S3.2 is obtained by mixing Bacillus velezensis ZLP-101 and Bacillus subtilis BSD-2 in a ratio of 1:1.

[0029] Furthermore, step S4: preparation of soil conditioner specifically comprises the following steps:

[0030] 30-50 parts by weight of sulfonated humic acid-chitosan coated Fe3O4@ZnO, 20-30 parts by weight of mature compost and 5-8 parts by weight of oyster shells are placed in a high-speed mixer and stirred at a speed of 1000-1200 rpm for 30-40 minutes to obtain a soil conditioner.

[0031] A soil conditioner for heavy metal contaminated soil is prepared by any of the above-mentioned processes for preparing a soil conditioner for heavy metal contaminated soil.

[0032] Compared with the prior art, the present invention has at least the following beneficial effects:

[0033] 1. The present invention mixes Fe3O4@ZnO coated with sulfonated humic acid-chitosan, decomposed compost and oyster shells. The oyster shells themselves have a certain particle structure. After being mixed into the soil, they can expand the gaps between soil particles, prevent the soil from being too compacted, increase the air permeability and water permeability of the soil, help plant roots to better stretch in the soil, and help water to penetrate and drain in the soil, thereby improving the porosity of the soil. The decomposed compost contains rich organic matter. After being applied to the soil, it can make the heavy soil looser and play a certain adhesive role for sandy soil with an overly loose texture, making the soil particles more suitable for plant growth, optimizing the overall texture of the soil, and enhancing the soil's water and fertilizer retention capacity. The Fe3O4@ZnO coated with sulfonated humic acid-chitosan can adsorb and fix heavy metals, thereby reducing the bioavailability of heavy metals and reducing the risk of their migration into the plant body, ensuring the quality and safety of agricultural products, and also contributing to the repair and improvement of the soil environment.

[0034] 2. The Fe3O4@ZnO in the present invention has a large specific surface area and strong adsorption properties, and can adsorb heavy metal ions in the soil, such as lead, cadmium, and mercury, reducing their activity and bioavailability in the soil, reducing the toxic effects of heavy metals on plants, and also preventing heavy metals from entering the human body through the food chain, thereby ensuring the quality and safety of agricultural products. On the one hand, Fe3O4@ZnO utilizes the polar surface of ZnO to adsorb heavy metals. On the other hand, Fe3O4 has superparamagnetism. When an external magnetic field is applied, it is easy to separate and recover the remediation agent adsorbed with heavy metals from the soil, preventing secondary pollution. In addition, it is wrapped with sulfonated humic acid-chitosan. The network wrapping structure formed by chitosan and sulfonated humic acid not only tightly wraps Fe3O4@ZnO to prevent its agglomeration and inactivation in the soil environment, but also provides more adsorption sites for heavy metal ions. This structure makes it difficult for the adsorbed heavy metals to be desorbed and released back into the soil. Even when conditions such as soil pH and redox potential change, it can still maintain a good heavy metal fixation effect, ensuring the long-term effectiveness of soil remediation.

[0035] 3. The present invention introduces sulfonic acid functional groups by sulfonating humic acid. The sulfonic acid groups can be highly ionized in aqueous solution, making the sulfonated humic acid carry more negative charges, which greatly enhances its ion exchange capacity with heavy metal ions (such as lead, cadmium, mercury, etc.) with positive charges in the soil. It can react chemically with heavy metal ions (such as lead, cadmium, mercury, etc.) in the soil to form stable complexes, desorbing and fixing heavy metal ions from the surface of soil particles. When the sulfonated humic acid is co-wrapped with Fe3O4@ZnO by chitosan, the sulfonic acid groups of the sulfonated humic acid can react with the chitosan molecular chains. The amino groups on the sulfonated humic acid interact with each other to form a more stable chemical bond or hydrogen bond network. This interaction makes the wrapping layer structure tighter and stronger, and is not easy to break or fall off in the complex soil environment, ensuring that the core Fe3O4@ZnO can continue to play a stable role and maintain the overall performance of the soil remediation agent. At the same time, sulfonated humic acid is rich in organic carbon, nitrogen, phosphorus and other nutrients, which can provide nutrients for soil microorganisms and promote their reproduction and activity. The microbial metabolism process can convert the insoluble nutrients in the soil into a form that can be absorbed and utilized by plants, indirectly improving soil fertility. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The accompanying drawings, which are incorporated herein and constitute a part of the specification, illustrate embodiments of the invention and, together with the description, further serve to explain the principles of the invention and to enable one skilled in the art to make and use the invention.

[0037] Figure 1 This is a flow chart of the preparation process of a soil conditioner for heavy metal contaminated soil used in an embodiment of the present invention. DETAILED DESCRIPTION

[0038] The following describes in detail the preparation process of a soil conditioner for heavy metal-contaminated soil provided by the present invention, with reference to the accompanying drawings and specific examples. It is also noted that, for the sake of completeness, the following examples are best and preferred embodiments, and those skilled in the art may employ alternative methods for implementing known techniques. Furthermore, the accompanying drawings are intended only to provide a more detailed description of the embodiments and are not intended to limit the present invention.

[0039] Example 1

[0040] A preparation process of a soil conditioner for heavy metal contaminated soil, such as Figure 1 As shown, the following steps are included:

[0041] S1: Preparation of Fe3O4@ZnO

[0042] S1.1: 10 parts by weight of FeCl3·6H2O, 80 parts by weight of sodium acetate, and 3 parts by weight of trisodium citrate were dissolved in 110 parts by weight of ethylene glycol. The mixture was stirred at 200 rpm at room temperature for 20 min, transferred to a sealed polytetrafluoroethylene-lined tube, and then heated to 200°C and maintained for 12 h. After the reaction was complete, the dark brown product was magnetically collected using an external magnetic field, washed, and vacuum dried at 50°C for 10 h to obtain Fe3O4 nanoparticles.

[0043] S1.2: Dissolve 20 parts by weight of Zn(OAc)2·2H2O and 40 parts by weight of sodium hydroxide in 80 parts by weight of deionized water, stir and mix at 200 rpm for 10 min, then add the Fe3O4 nanoparticles and disperse them under ultrasonication for 20 min to obtain a mixed solution;

[0044] S1.3: The mixed solution was transferred to a sealed polytetrafluoroethylene-lined tube, then heated to 160°C and maintained for 12 h. After the reaction was complete, the dark brown product was magnetically collected using an external magnetic field, washed, and vacuum dried at 50°C for 10 h to obtain Fe3O4@ZnO.

[0045] S2: Preparation of sulfonated humic acid-chitosan coated Fe3O4@ZnO

[0046] S2.1: Add 10 parts by weight of humic acid to 10 parts by weight of a 15% volume fraction H2SO4 solution, stir to mix, and evenly spread the mixture in a Petri dish. Place the Petri dish in an oven, heat to 50°C, and react for 3 hours. After the sulfonation reaction is complete, cool to room temperature to obtain sulfonated humic acid.

[0047] S2.2: Weigh 5 parts by weight of chitosan powder and dissolve it in 1% acetic acid solution. Stir at room temperature for 4 hours until the chitosan is completely dissolved to prepare a 5 g / L chitosan solution. Simultaneously, prepare a 10 g / L aqueous solution of sulfonated humic acid.

[0048] S2.3: 10 parts by weight of Fe3O4@ZnO were dispersed in 30 parts by weight of deionized water, and ultrasonically dispersed for 40 minutes to obtain a Fe3O4@ZnO dispersion. 3 parts by weight of a sulfonated humic acid aqueous solution were then added, and the mixture was stirred at room temperature for 3 hours. 3 parts by weight of a chitosan solution and 0.5 parts by weight of a 0.5% glutaraldehyde were then added, and the pH value of the solution was adjusted to 5. The mixture was stirred at 40°C for 3 hours. After the reaction, the mixture was washed twice with deionized water and separated using an external magnetic field to obtain sulfonated humic acid-chitosan coated Fe3O4@ZnO.

[0049] S3: Preparation of mature compost

[0050] S3.1: Collect organic waste such as crop straw, livestock and poultry manure, and fallen leaves, and mix them in a ratio of 3:2:1 to obtain compost raw materials. Select an open area with high terrain, good drainage, and good ventilation. Lay a 20cm thick layer of gravel on the ground, and then spread 10cm of coarse sand on the gravel layer. Set up a fence around the site with a height of 1m to obtain a composting site.

[0051] S3.2: Pile the mixed compost materials into a trapezoidal pile with a base width of 2m, a height of 1.5m, and a top width of 1m at the composting site. The weight of each pile should be controlled at 3 tons. In the early stages of composting, use a watering can to evenly spray the materials with clean water to a moisture content of 50%. Then, add 1% of the composite microbial inoculant.

[0052] S3.3: During the first week of composting, monitor the material temperature daily. When the temperature reaches 50°C, enter the high-temperature maturity stage, which lasts for 3 weeks. Turn the compost every 3 days during this period. When the material temperature gradually decreases, enter the post-maturity stage, which lasts for 2 weeks. Maintain the moisture content at 40%. After 3 months of complete composting, mature compost is obtained.

[0053] The composite microbial agent is prepared by mixing Bacillus velezensis ZLP-101 and Bacillus subtilis BSD-2 in a ratio of 1:1;

[0054] S4: Preparation of soil conditioner

[0055] 30 parts by weight of sulfonated humic acid-chitosan coated Fe3O4@ZnO, 20 parts by weight of mature compost and 5 parts by weight of oyster shells were placed in a high-speed mixer and stirred at a speed of 1000 rpm for 30 minutes to obtain a soil conditioner.

[0056] Example 2

[0057] A preparation process of a soil conditioner for heavy metal contaminated soil, such as Figure 1 As shown, the following steps are included:

[0058] S1: Preparation of Fe3O4@ZnO

[0059] S1.1: 12 parts by weight of FeCl3·6H2O, 90 parts by weight of sodium acetate, and 5 parts by weight of trisodium citrate were dissolved in 120 parts by weight of ethylene glycol. The mixture was stirred at 200 rpm at room temperature for 20 min, transferred to a polytetrafluoroethylene-lined tube, and sealed. The temperature was then raised to 200°C and maintained for 12 h. After the reaction was complete, the dark brown product was magnetically collected using an external magnetic field, washed, and vacuum dried at 50°C for 10 h to obtain Fe3O4 nanoparticles.

[0060] S1.2: Dissolve 30 parts by weight of Zn(OAc)2·2H2O and 50 parts by weight of sodium hydroxide in 100 parts by weight of deionized water, stir and mix at 200 rpm for 10 min, then add the above-mentioned Fe3O4 nanoparticles and ultrasonically disperse for 20 min to obtain a mixed solution;

[0061] S1.3: The mixed solution was transferred to a sealed polytetrafluoroethylene-lined tube, then heated to 160°C and maintained for 12 h. After the reaction was complete, the dark brown product was magnetically collected using an external magnetic field, washed, and vacuum dried at 50°C for 10 h to obtain Fe3O4@ZnO.

[0062] S2: Preparation of sulfonated humic acid-chitosan coated Fe3O4@ZnO

[0063] S2.1: Add 12 parts by weight of humic acid to 12 parts by weight of a 15% by volume H2SO4 solution, stir to mix, and evenly spread the mixture in a Petri dish. Place the Petri dish in an oven and heat to 50°C for 3 hours. After the sulfonation reaction is complete, cool to room temperature to obtain sulfonated humic acid.

[0064] S2.2: Weigh 8 parts by weight of chitosan powder and dissolve it in 3% acetic acid solution. Stir at room temperature for 4 hours until the chitosan is completely dissolved to prepare a chitosan solution with a concentration of 10 g / L. Simultaneously, prepare a 20 g / L aqueous solution of sulfonated humic acid.

[0065] S2.3: 12 parts by weight of Fe3O4@ZnO were dispersed in 50 parts by weight of deionized water, and ultrasonically dispersed for 40 minutes to obtain a Fe3O4@ZnO dispersion. 5 parts by weight of sulfonated humic acid aqueous solution were then added, and the mixture was stirred at room temperature for 3 hours. 4 parts by weight of chitosan solution and 0.5 parts by weight of 1% glutaraldehyde were then added, and the pH value of the solution was adjusted to 6. The mixture was stirred at 40°C for 3 hours. After the reaction, the mixture was washed twice with deionized water and separated using an external magnetic field to obtain sulfonated humic acid-chitosan coated Fe3O4@ZnO;

[0066] S3: Preparation of mature compost

[0067] S3.1: Collect organic waste such as crop straw, livestock and poultry manure, and fallen leaves, and mix them in a ratio of 3:2:2 to obtain compost raw materials. Select an open area with high terrain, good drainage, and good ventilation. Lay a 30cm thick layer of gravel on the ground, and then cover the gravel layer with 15cm of coarse sand. Set up a fence around the site to a height of 1.5m to obtain a composting site.

[0068] S3.2: Pile the mixed compost materials into a trapezoidal pile with a base width of 3m, a height of 2m, and a top width of 1.5m at the composting site. The weight of each pile should be controlled at 5 tons. In the early stages of composting, use a watering can to evenly spray the materials with clean water to a moisture content of 60%. Then, add 2% of the composite microbial inoculant.

[0069] S3.3: During the first week of composting, monitor the material temperature daily. When the temperature reaches 50°C, it enters the high-temperature maturity stage, which lasts for 3 weeks. During this period, the compost is turned every 3 days. As the material temperature gradually decreases, it enters the post-maturity stage, which lasts for 2 weeks. The moisture content is maintained at 50%. After 3 months of complete composting, mature compost is obtained.

[0070] The composite microbial agent is prepared by mixing Bacillus velezensis ZLP-101 and Bacillus subtilis BSD-2 in a ratio of 1:1;

[0071] S4: Preparation of soil conditioner

[0072] 50 parts by weight of sulfonated humic acid-chitosan coated Fe3O4@ZnO, 30 parts by weight of mature compost and 8 parts by weight of oyster shells were placed in a high-speed mixer and stirred at a speed of 1000 rpm for 30 minutes to obtain a soil conditioner.

[0073] Example 3

[0074] A preparation process of a soil conditioner for heavy metal contaminated soil, such as Figure 1 As shown, the following steps are included:

[0075] S1: Preparation of Fe3O4@ZnO

[0076] S1.1: 10 parts by weight of FeCl3·6H2O, 80 parts by weight of sodium acetate, and 3 parts by weight of trisodium citrate were dissolved in 110 parts by weight of ethylene glycol. The mixture was stirred at 300 rpm at room temperature for 30 min, transferred to a polytetrafluoroethylene-lined tube, and sealed. The temperature was then raised to 220°C and maintained for 14 h. After the reaction was complete, the dark brown product was magnetically collected using an external magnetic field, washed, and vacuum dried at 60°C for 12 h to obtain Fe3O4 nanoparticles.

[0077] S1.2: Dissolve 20 parts by weight of Zn(OAc)2·2H2O and 40 parts by weight of sodium hydroxide in 80 parts by weight of deionized water, stir and mix at 230 rpm for 20 min, then add the Fe3O4 nanoparticles and ultrasonically disperse for 30 min to obtain a mixed solution;

[0078] S1.3: The mixed solution was transferred to a sealed polytetrafluoroethylene-lined tube, then heated to 180°C and maintained for 14 h. After the reaction was complete, the dark brown product was magnetically collected using an external magnetic field, washed, and vacuum dried at 60°C for 12 h to obtain Fe3O4@ZnO.

[0079] S2: Preparation of sulfonated humic acid-chitosan coated Fe3O4@ZnO

[0080] S2.1: Add 10 parts by weight of humic acid to 10 parts by weight of a 15% by volume H2SO4 solution, stir to mix, and evenly spread the mixture in a Petri dish. Place the Petri dish in an oven, heat to 60°C, and react for 4 hours. After the sulfonation reaction is complete, cool to room temperature to obtain sulfonated humic acid.

[0081] S2.2: Weigh 5 parts by weight of chitosan powder and dissolve it in 1% acetic acid solution. Stir at room temperature for 6 hours until the chitosan is completely dissolved to prepare a 5 g / L chitosan solution. Simultaneously, prepare a 10 g / L aqueous solution of sulfonated humic acid.

[0082] S2.3: 10 parts by weight of Fe3O4@ZnO were dispersed in 30 parts by weight of deionized water, and ultrasonically dispersed for 50 minutes to obtain a Fe3O4@ZnO dispersion. 3 parts by weight of a sulfonated humic acid aqueous solution were then added, and the mixture was stirred at room temperature for 4 hours. 3 parts by weight of a chitosan solution and 0.5 parts by weight of 0.5% glutaraldehyde were then added, and the pH value of the solution was adjusted to 5. The mixture was stirred at 50°C for 5 hours. After the reaction, the mixture was washed three times with deionized water and separated using an external magnetic field to obtain sulfonated humic acid-chitosan coated Fe3O4@ZnO.

[0083] S3: Preparation of mature compost

[0084] S3.1: Collect organic waste such as crop straw, livestock and poultry manure, and fallen leaves, and mix them in a ratio of 3:2:1 to obtain compost raw materials. Select an open area with high terrain, good drainage, and good ventilation. Lay a 20cm thick layer of gravel on the ground, and then spread 10cm of coarse sand on the gravel layer. Set up a fence around the site with a height of 1m to obtain a composting site.

[0085] S3.2: Pile the mixed compost materials into a trapezoidal pile with a base width of 2m, a height of 1.5m, and a top width of 1m at the composting site. The weight of each pile should be controlled at 3 tons. In the early stages of composting, use a watering can to evenly spray the materials with clean water to a moisture content of 50%. Then, add 1% of the composite microbial inoculant.

[0086] S3.3: During the second week of composting, monitor the material temperature daily. When the temperature reaches 65°C, it enters the high-temperature maturity stage, which lasts for 4 weeks. During this period, the compost is turned every 4 days. When the temperature gradually decreases, it enters the post-maturity stage, which lasts for 3 weeks. The moisture content is maintained at 40%. After 6 months of complete composting, mature compost is obtained.

[0087] The composite microbial agent is prepared by mixing Bacillus velezensis ZLP-101 and Bacillus subtilis BSD-2 in a ratio of 1:1;

[0088] S4: Preparation of soil conditioner

[0089] 30 parts by weight of sulfonated humic acid-chitosan coated Fe3O4@ZnO, 20 parts by weight of decomposed compost and 5 parts by weight of oyster shells were placed in a high-speed mixer and stirred at a speed of 1200 rpm for 40 minutes to obtain a soil conditioner.

[0090] Comparative Example 1

[0091] Compared with Example 1, the difference of Comparative Example 1 is that Comparative Example 1 removes step S2, replaces the sulfonated humic acid-chitosan-coated Fe3O4@ZnO in step S4 with Fe3O4@ZnO, and prepares the soil conditioner without changing the other steps, which is recorded as Comparative Example 1.

[0092] Comparative Example 2

[0093] Compared with Example 1, the difference of Comparative Example 2 is that step S2.1 is removed in Comparative Example 2, and step S2.2 is modified to prepare a 10 g / L humic acid aqueous solution, the sulfonated humic acid aqueous solution in step 2.3 is replaced by a humic acid aqueous solution, and finally step S2.3 obtains humic acid-chitosan-coated Fe3O4@ZnO, and the sulfonated humic acid-chitosan-coated Fe3O4@ZnO in step S4 is replaced by humic acid-chitosan-coated Fe3O4@ZnO. The remaining steps remain unchanged to prepare the soil conditioner, which is recorded as Comparative Example 2.

[0094] The treatment effects of the soil conditioners prepared in Examples 1-3 and Comparative Examples 1-2 on heavy metals in the soil were determined using the following test methods:

[0095] Weigh 100 g of contaminated soil into a 1 L beaker, add 500 mL of deionized water and 5 g of soil conditioner, and stir for 7 days. Then, dry the contaminated soil at 100 °C before and after treatment. After digestion and constant volume, filter, and measure the heavy metal content of the contaminated soil before and after treatment using an atomic absorption spectrophotometer. The heavy metal removal rate is calculated using the following formula:

[0096] Removal rate (%) = (H0-H1) / H0×100; where H0 is the heavy metal content in the soil before treatment, and H1 is the heavy metal content in the soil after treatment; the test results are shown in Table 1.

[0097] Table 1. Heavy metal removal rates in soils of Examples 1-3 and Comparative Examples 1-2

[0098] Cd% Hg% Pb% Example 1 93.2 91.5 97.3 Example 2 94.5 92.6 98.4 Example 3 93.7 92.1 97.6 Comparative Example 1 73.4 71.2 75.3 Comparative Example 2 83.2 79.3 84.2

[0099] The data in Table 1 show that Examples 1-3 have a heavy metal removal rate in the soil exceeding 90%, indicating that the soil conditioner prepared by the present invention can reduce the bioavailability of heavy metals, reduce the risk of their migration into plant bodies, and ensure the quality and safety of agricultural products. The data in Comparative Example 1 show that the heavy metal removal rate is significantly reduced, indicating that the use of sulfonated humic acid-chitosan for encapsulation can improve the adsorption capacity for heavy metals, maintain a good heavy metal fixation effect, and ensure the long-term effectiveness of soil remediation. The data in Comparative Example 2 show that the introduction of sulfonic acid functional groups by sulfonating humic acid can further desorb and fix heavy metal ions from the surface of soil particles, thereby improving the removal effect of heavy metals in the soil.

[0100] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the present invention. Anyone skilled in the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by one of ordinary skill in the art without departing from the spirit and technical principles disclosed herein are intended to be covered by the claims of the present invention.

Claims

1. A preparation process for a soil conditioner for heavy metal contaminated soil, characterized in that: The steps include: S1: Preparation of Fe3O4@ZnO Zn(OAc)2·2H2O and sodium hydroxide were dissolved in deionized water, and then Fe3O4 nanoparticles were added to obtain a mixed solution. The mixed solution was transferred to a polytetrafluoroethylene liner and sealed. The temperature was then raised to react to prepare Fe3O4@ZnO. S2: Preparation of sulfonated humic acid-chitosan coated Fe3O4@ZnO Sulfonated humic acid aqueous solution and chitosan solution were prepared, Fe3O4@ZnO was dispersed in deionized water, and then the sulfonated humic acid aqueous solution, chitosan solution and glutaraldehyde were added to react to obtain sulfonated humic acid-chitosan coated Fe3O4@ZnO; S3: Preparation of mature compost Composting crop straw, livestock and poultry manure, fallen leaves and other organic waste; S4: Preparation of soil conditioner A soil conditioner is obtained by mixing 30-50 parts by weight of sulfonated humic acid-chitosan coated Fe3O4@ZnO, 20-30 parts by weight of decomposed compost and 5-8 parts by weight of oyster shells.

2. The preparation process of a soil conditioner for heavy metal contaminated soil according to claim 1, characterized in that: Step S1: Preparation of Fe3O4@ZnO, specifically comprising the following steps: S1.1: Dissolve 10-12 parts by weight of FeCl3·6H2O, 80-90 parts by weight of sodium acetate, and 3-5 parts by weight of trisodium citrate in 110-120 parts by weight of ethylene glycol. Stir the mixture at 200-300 rpm for 20-30 minutes at room temperature, transfer the mixture to a sealed polytetrafluoroethylene-lined tube, and then heat the tube to 200-220°C and maintain the temperature for 12-14 hours. After the reaction is complete, magnetically collect the dark brown product using an external magnetic field, wash it, and vacuum dry it at 50-60°C for 10-12 hours to obtain Fe3O4 nanoparticles. S1.2: Dissolve 20-30 parts by weight of Zn(OAc)2·2H2O and 40-50 parts by weight of sodium hydroxide in 80-100 parts by weight of deionized water, stir and mix at 200-230 rpm for 10-20 min, then add the Fe3O4 nanoparticles and ultrasonically disperse for 20-30 min to obtain a mixed solution; S1.3: Transfer the mixed solution to a sealed polytetrafluoroethylene-lined tube, then heat to 160-180°C and maintain for 12-14 hours. When the reaction is complete, magnetically collect the dark brown product using an external magnetic field. After washing, vacuum dry it at 50-60°C for 10-12 hours to obtain Fe3O4@ZnO.

3. The preparation process of a soil conditioner for heavy metal contaminated soil according to claim 2, characterized in that: Step S2: Preparation of sulfonated humic acid-chitosan coated Fe3O4@ZnO, specifically comprising the following steps: S2.1: Add 10-12 parts by weight of humic acid to 10-12 parts by weight of a 15% volume fraction H2SO4 solution, stir to mix, and evenly spread the mixture in a Petri dish. Place the Petri dish in an oven and heat to 50-60°C for 3-4 hours. After the sulfonation reaction is complete, cool to room temperature to obtain sulfonated humic acid. S2.2: Weigh 5-8 parts by weight of chitosan powder and dissolve it in 1-3% acetic acid solution. Stir at room temperature for 4-6 hours until the chitosan is completely dissolved to prepare a chitosan solution with a concentration of 5-10 g / L. Simultaneously, prepare a 10-20 g / L aqueous solution of sulfonated humic acid. S2.3: Disperse 10-12 parts by weight of Fe3O4@ZnO in 30-50 parts by weight of deionized water, ultrasonically disperse for 40-50 minutes to obtain a Fe3O4@ZnO dispersion, then add 3-5 parts by weight of a sulfonated humic acid aqueous solution, and continue stirring at room temperature for 3-4 hours. Then, add 3-4 parts by weight of a chitosan solution and 0.5-0.8 parts by weight of 0.5-1% glutaraldehyde, and adjust the pH value of the solution to 5-6. Stir and react at 40-50°C for 3-5 hours. After the reaction, wash with deionized water 2-3 times, and separate using an external magnetic field to obtain sulfonated humic acid-chitosan-encapsulated Fe3O4@ZnO.

4. The preparation process of a soil conditioner for heavy metal contaminated soil according to claim 3, characterized in that: Step S3: Preparation of mature compost, specifically comprising the following steps: S3.1: Collect organic waste such as crop straw, livestock and poultry manure, and fallen leaves, and mix them in a ratio of 3:2:1-2 to obtain compost raw materials. Select an open area with high terrain, good drainage, and smooth ventilation. Lay a 20-30 cm thick layer of gravel on the ground, and then spread 10-15 cm of coarse sand on the gravel layer. Set up a fence around the site with a height of 1-1.5 m to obtain a composting site. S3.2: Pile the mixed compost materials into a trapezoidal pile with a base width of 2-3m, a height of 1.5-2m, and a top width of 1-1.5m at the composting site. The weight of each pile should be controlled at 3-5 tons. In the early stages of composting, use a watering can to evenly spray the materials with clean water to a moisture content of 50-60%. Then, add 1-2% of a composite microbial agent. S3.3: During the first 1-2 weeks of composting, the material temperature is monitored every day. When the temperature rises to 50-65℃, it enters the high-temperature decomposition period, which lasts for 3-4 weeks. During this period, the pile is turned over every 3-4 days. When the temperature gradually drops, it enters the post-decomposition period, which lasts for 2-3 weeks. The moisture content is maintained at 40-50%. After 3-6 months of complete decomposition process, mature compost is obtained.

5. The preparation process of a soil conditioner for heavy metal contaminated soil according to claim 4, characterized in that: The composite microbial agent in step S3.2 is obtained by mixing Bacillus Velez ZLP-101 and Bacillus subtilis BSD-2 in a ratio of 1:

1.

6. The process for preparing a soil conditioner for heavy metal contaminated soil according to claim 5, characterized in that: Step S4: Preparation of soil conditioner, specifically comprising the following steps: 30-50 parts by weight of sulfonated humic acid-chitosan coated Fe3O4@ZnO, 20-30 parts by weight of mature compost and 5-8 parts by weight of oyster shells are placed in a high-speed mixer and stirred at a speed of 1000-1200 rpm for 30-40 minutes to obtain a soil conditioner.

7. A soil conditioner for heavy metal contaminated soil, characterized in that: The soil conditioner is prepared by the preparation process of a soil conditioner for heavy metal contaminated soil according to any one of claims 1 to 6.

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