Preparation and application of a cadmium passivating agent for weakly alkaline soils

Abstract

This invention belongs to the field of heavy metal pollution remediation technology, and relates to the preparation and application of a cadmium passivating agent for weakly alkaline soil. The weakly alkaline soil cadmium passivating agent mainly comprises the following components by weight: 30-50 parts of a mineral complex, 40-60 parts of a bioactive component, and 5-15 parts of an auxiliary stabilizer. The mineral complex includes natural sepiolite, calcium-based bentonite, and a polyether-polyester diblock copolymer; the bioactive component includes microbial agents, phosphorus-modified biochar, lecithin, and phosphatidylserine; and the auxiliary stabilizer includes nano-hydroxyapatite and a chitosan-grafted polyaspartic acid complex. This weakly alkaline soil cadmium passivating agent exhibits excellent remediation effects on cadmium in contaminated soil, effectively preventing or reducing the entry of cadmium and other heavy metals into the food chain, and has significant market potential.

Description

Technical Field

[0001] This invention belongs to the field of heavy metal pollution control technology, and relates to the preparation and application of a cadmium passivating agent for weakly alkaline soil. Background Technology

[0002] Cadmium in soil originates from various sources, including atmospheric deposition, industrial and domestic wastewater discharge, industrial solid waste and urban garbage dumping, and the application of chemical pesticides. Cadmium in soil exhibits significant characteristics such as concealment, bioaccumulation, irreversibility, and difficulty in remediation. It impacts crops, air and water quality, ultimately manifesting in the food chain and accumulating in the human body, leading to physiological disorders and even diseases such as lung cancer and kidney failure.

[0003] Unlike organic pollution, the core issue with heavy metal pollution is its non-degradability. Only by removing heavy metals from the soil or altering their valence and form within the soil, thereby reducing their migration and bioavailability in the environment, can the remediation of heavy metal-contaminated soil be achieved.

[0004] Alkaline soils include slightly alkaline soils (pH generally 7.1-8.5) and strongly alkaline soils (pH generally 8.5-9.5). Alkaline soils have a higher pH and lower organic matter content. In northern China, farmland is mainly dryland, and the soil is in an oxidized state most of the time, making it difficult to reduce the available heavy metal content in the soil by increasing soil pH or continuous flooding. Further application of high-pH soil conditioners or passivating agents to moderately alkaline soils carries risks such as soil compaction and reduced fertility. Currently, there are few passivating agents suitable for cadmium-contaminated alkaline soils, necessitating the development of cadmium passivating agents with significant passivation effects on slightly alkaline soils. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide a preparation and application of a cadmium passivating agent for weakly alkaline soils. This weakly alkaline cadmium passivating agent has a significant passivation effect on cadmium-contaminated soils, effectively removes cadmium from weakly alkaline soils, and improves the environment of heavy metal-contaminated soils.

[0006] To achieve the above objectives, this application adopts the following technical solution:

[0007] This invention provides a weakly alkaline soil cadmium passivating agent, which mainly comprises the following components by weight: 30-50 parts of a mineral complex, 40-60 parts of a bioactive component, and 5-15 parts of an auxiliary stabilizer; wherein, the mineral complex includes natural sepiolite, calcium-based bentonite, and a polyether-polyester diblock copolymer; the bioactive component includes microbial inoculants, phosphorus-modified biochar, lecithin, and phosphatidylserine; the auxiliary stabilizer includes nano-hydroxyapatite and a chitosan-grafted polyaspartic acid complex; the microbial inoculant is a compound inoculant composed of Bacillus subtilis, Bacillus amyloliquefaciens, Bacillus thuringiensis, and Pseudomonas nitroreductoids.

[0008] Furthermore, the weakly alkaline soil cadmium passivating agent mainly comprises the following components by weight: 20-30 parts of natural sepiolite, 8-12 parts of calcium-based bentonite, 2-8 parts of polyether-polyester diblock copolymer, 8-12 parts of microbial inoculant, 26-35 parts of phosphorus-modified biochar, 6-10 parts of lecithin, 1-3 parts of phosphatidylserine, 4-12 parts of nano-hydroxyapatite, and 1-3 parts of chitosan-grafted polyaspartic acid complex; more preferably, it comprises 25 parts of natural sepiolite, 10 parts of calcium-based bentonite, 5 parts of polyether-polyester diblock copolymer, 10 parts of microbial inoculant, 30 parts of phosphorus-modified biochar, 8 parts of lecithin, 2 parts of phosphatidylserine, 8 parts of nano-hydroxyapatite, and 2 parts of chitosan-grafted polyaspartic acid complex.

[0009] Furthermore, in the weakly alkaline soil cadmium passivating agent, the polyether-polyester diblock copolymer is one or more of the following: polyethylene glycol-polylactide, polyethylene glycol monomethyl ether-polylactide, polyethylene glycol-polylactide-lactide, polyethylene glycol-polycaprolactone, polyethylene glycol-polyorthoester, polypropylene glycol-polylactide, or polybutanediol-polylactide; preferably, the polyether-polyester diblock copolymer is polyethylene glycol 2000-polylactide 2000 or polyethylene glycol monomethyl ether 2000-polylactide 2000.

[0010] Furthermore, in the weakly alkaline soil cadmium passivating agent, the microbial inoculant contains Bacillus subtilis, Bacillus amyloliquefaciens, Bacillus thuringiensis, and Pseudomonas nitroreductoids in a microbial mass ratio of 2-4:4-6:1-3:0.5-1, and the effective viable count of each of the Bacillus subtilis, Bacillus amyloliquefaciens, Bacillus thuringiensis, and Pseudomonas nitroreductoids is ≥1.0 × 10⁻⁶. 9 cfu·g -1 The effective viable count of the compound microbial agent is ≥5.0×10⁻⁶. 9 cfu·g -1Further preferably, the microbial mass ratio of Bacillus subtilis, Bacillus amyloliquefaciens, Bacillus thuringiensis, and Pseudomonas nitroreductoids is 3:5:2:1.

[0011] Furthermore, the weakly alkaline soil cadmium passivating agent mainly comprises the following components by weight: 25 parts of natural sepiolite, 10 parts of calcium-based bentonite, 5 parts of polyethylene glycol 2000-polylactide 2000 or polyethylene glycol monomethyl ether 2000-polylactide 2000, 10 parts of microbial inoculant, 30 parts of phosphorus-modified biochar, 8 parts of lecithin, 2 parts of phosphatidylserine, 8 parts of nano-hydroxyapatite, and 2 parts of chitosan-grafted polyaspartic acid complex; the microbial inoculant is composed of Bacillus subtilis, Bacillus amyloliquefaciens, Bacillus thuringiensis, and Pseudomonas nitroreductoids in a microbial mass ratio of 3:5:2:1.

[0012] In the preferred embodiment of the present invention, the weakly alkaline soil cadmium passivating agent, the preparation method of the polyethylene glycol 2000-polylactide 2000 is as follows: polyethylene glycol 2000 is added to a polymerization flask, kept warm and stirred, and vacuumed to remove water. Stannous octoate / toluene solution is added, stirred and dispersed, kept warm and stirred, and vacuumed to remove toluene. Polylactide 2000 is then added, and the reaction is carried out by stirring and keeping warm. After the reaction is completed, the temperature is lowered, an organic solvent is added and stirred to dissolve, a metal removal agent is added for treatment, and the mixture is filtered. The filtrate is added to anhydrous diethyl ether, dissolved and crystallized, and then dissolved again. The mixture is filtered through a PTFE membrane, and the filtrate is added to anhydrous diethyl ether to crystallize. The mixture is filtered, and the filter cake is dried to obtain a polyethylene glycol 2000-polylactide 2000 diblock copolymer.

[0013] The polyether-polyester diblock copolymer, consisting of polyethylene glycol 2000-polylactide 2000 and polyethylene glycol monomethyl ether 2000-polylactide 2000, was found to exhibit a synergistic effect of targeted adsorption-biodegradation-stabilization and solidification, superior to other forms of diblock copolymers. The mineral complex rapidly captures cadmium ions through the layered pores of natural sepiolite and calcium-based bentonite; the bioactive component degrades cadmium toxicity through microbial agents, while phosphorus-modified biochar adsorption and lecithin-based substances regulate compatibility and enhance passivation effects; auxiliary stabilizers ensure the system's long-term effectiveness and environmental adaptability, guaranteeing stable operation in complex soils.

[0014] A second aspect of the present invention provides the aforementioned weakly alkaline soil cadmium passivating agent, the preparation method of which is as follows:

[0015] Preparation of S1 mineral complex: Natural sepiolite and calcium-based bentonite were dried, pulverized, sieved to remove impurities, mixed evenly, and polyether-polyester diblock copolymer was added and mixed further; the mixture was heated and activated under inert gas protection, cooled, ground and sieved to obtain a highly active mineral complex, which was sealed and protected from light for later use.

[0016] Preparation of S2 composite microbial inoculant: Mix multiple microbial inoculants evenly, enrich the bacterial cells by centrifugation, add a protectant and freeze-dry under vacuum to obtain composite microbial powder;

[0017] Preparation of S3 phosphorus-modified biochar: Peanut shells and corn cobs are mixed, dried, crushed and sieved to obtain biomass raw materials; the biomass raw materials are mixed with phosphorus source solution, soaked and stirred, filtered and drained, pyrolyzed under inert gas protection, cooled, ground and sieved, washed until neutral and then dried to obtain phosphorus-modified biochar for later use.

[0018] S4 Bioactive Component Compound: Mix phosphorus-modified biochar, lecithin, and phosphatidylserine evenly according to the formula, add compound microbial powder, and stir and mix evenly at low temperature to obtain a bioactive complex. Seal and store at low temperature for later use.

[0019] S5 auxiliary stabilizer pretreatment: After crushing and sieving nano hydroxyapatite, it is mixed evenly with chitosan-grafted polyaspartic acid complex according to the ratio to obtain pretreated auxiliary stabilizer for later use.

[0020] S6 Finished Product Molding: The mineral complex, bioactive complex, and auxiliary stabilizer are added to the mixing equipment according to the weight parts, and mixed at low temperature until uniform and free of lumps. After grinding and sieving to remove coarse particles, the finished product is obtained.

[0021] Furthermore, the above preparation method is described in more detail as follows:

[0022] Preparation of S1 mineral complex: Natural sepiolite and calcium-based bentonite were dried in a hot air drying oven at 60-65℃ for 8-10 hours, pulverized, and passed through a 120-mesh standard sieve to remove impurities. Then, they were added to a high-speed mixer and mixed at 300-400 r / min at room temperature for 15-20 minutes. Polyether-polyester diblock copolymer was slowly added and mixed for another 25-30 minutes until homogeneous. The mixture was then transferred to a nitrogen-protected activation furnace and activated at 350-400℃ at 5-8℃ / min for 1.5-2 hours. After cooling to room temperature, the mixture was ground and passed through a 120-mesh sieve to obtain a highly active mineral complex. The complex was then sealed and protected from light for later use.

[0023] Preparation of S2 composite microbial agent: The microbial agent is mixed evenly, the bacterial cells are separated by centrifugation and precipitation, then galactose protectant is added, and the mixture is freeze-dried under vacuum to obtain composite microbial powder;

[0024] Preparation of S3 phosphorus-modified biochar: Peanut shells and corn cobs were mixed at a mass ratio of 1:1, dried at 60℃ for 12 hours, and pulverized through a 100-mesh sieve to obtain biomass raw materials; the biomass raw materials were mixed with a 10% mass concentration potassium dihydrogen phosphate solution at a solid-liquid ratio of 1:3, soaked at 25-35℃ for 8-15 hours, and stirred 2-3 times; the soaked material was filtered and drained, placed in a nitrogen-protected pyrolysis furnace, heated at 10℃ / min to 500-550℃ for pyrolysis for 2.5-3 hours, cooled to room temperature, ground through a 100-mesh sieve, washed with deionized water until neutral, and dried at 60℃ to obtain phosphorus-modified biochar for later use.

[0025] Preparation of S4 bioactive component compound: According to the bioactive component ratio, add phosphorus-modified biochar, lecithin, and phosphatidylserine to a mixer and mix at 250 r / min at room temperature for 20 min. Add the prepared compound microbial powder and stir at ≤25℃ at low speed for 15 min (to avoid high temperature inactivation) until the system is homogeneous to obtain the bioactive complex. Seal and store at low temperature for later use.

[0026] Pretreatment of S5 auxiliary stabilizer: Nano-hydroxyapatite was pulverized and passed through a 120-mesh sieve, and then added to a high-speed mixer in proportion with the chitosan-grafted polyaspartic acid complex. The mixture was mixed at 300 r / min for 15 min to obtain the pretreated auxiliary stabilizer for later use.

[0027] S6 Finished Passivating Agent Molding: Homogenization: Add the mineral complex, bioactive complex, and auxiliary stabilizer to a double helix conical mixer according to the weight ratio, and mix at 150~200r / min for 30~40min at a low temperature of ≤28℃ until all components are evenly dispersed and free of lumps; grind the mixture through a 100-mesh standard sieve to remove coarse particle impurities, and the finished weakly alkaline soil cadmium passivating agent is obtained.

[0028] In the preferred embodiment of the present invention, a weakly alkaline soil cadmium passivating agent is provided, which mainly comprises the following components by weight: 40 parts of a mineral complex, 50 parts of a bioactive component, and 10 parts of an auxiliary stabilizer; wherein, the mineral complex includes natural sepiolite, calcium-based bentonite, and polyethylene glycol 2000-polylactide 200 diblock copolymer; the bioactive component includes microbial inoculant, phosphorus-modified biochar, lecithin, and phosphatidylserine; the auxiliary stabilizer includes nano-hydroxyapatite and chitosan-grafted polyaspartic acid complex; the microbial inoculant is Bacillus subtilis spores. The compound microbial agent is composed of Bacillus subtilis, Bacillus amyloliquefaciens, Bacillus thuringiensis, and Pseudomonas nitroreductoids; the composition includes 25 parts of natural sepiolite, 10 parts of calcium-based bentonite, 5 parts of polyethylene glycol 2000-polylactide 2000 diblock copolymer, 10 parts of microbial agent, 30 parts of phosphorus-modified biochar, 8 parts of lecithin, 2 parts of phosphatidylserine, 8 parts of nano-hydroxyapatite, and 2 parts of chitosan-grafted polyaspartic acid complex; the microbial agent is composed of Bacillus subtilis, Bacillus amyloliquefaciens, Bacillus thuringiensis, and Pseudomonas nitroreductoids in a microbial mass ratio of 3:5:2:1.

[0029] Furthermore, the weakly alkaline soil cadmium passivating agent described in this invention is applied in the in-situ remediation of heavy metal pollution in soil. The heavy metal pollution is cadmium pollution.

[0030] The present invention provides a method for using the above-mentioned weakly alkaline soil cadmium passivating agent, wherein the method is: applying the composite heavy metal passivating agent to heavy metal contaminated soil and then tilling it.

[0031] Furthermore, when the application environment is potted plants, the application amount of the weakly alkaline soil cadmium passivating agent is 0.5%-1.8% of the weight of the potted soil; when the application environment is open field, the application amount of the weakly alkaline soil cadmium passivating agent is 100-200 kg / mu.

[0032] The beneficial effects achieved by this invention are as follows:

[0033] 1) This weakly alkaline soil cadmium passivation agent is composed of a mineral complex, a bioactive component, and an auxiliary stabilizer, adhering to the synergistic concept of "targeted adsorption-biodegradation-stabilization and solidification". The mineral complex relies on the layered pores of natural sepiolite and calcium-based bentonite to rapidly capture cadmium ions; the bioactive component degrades cadmium toxicity through microbial agents, and is combined with phosphorus-modified biochar adsorption and lecithin-based substances to regulate compatibility and enhance the passivation effect; the auxiliary stabilizer ensures the long-term effectiveness and environmental adaptability of the system, ensuring stable operation in complex soils.

[0034] 2) This invention selects polyether-polyester diblock copolymers, especially polyethylene glycol 2000-polylactide 2000 or polyethylene glycol monomethyl ether 2000-polylactide 2000, which can form hydrogen bonds with hydroxyl groups on the mineral surface, bridge mineral particles to avoid agglomeration, and construct through adsorption channels; the polyether segments enhance structural toughness and reduce tillage losses.

[0035] 3) Chitosan-grafted polyaspartic acid complex can disperse and stabilize various components, encapsulate and protect microbial agents, help maintain a weakly alkaline soil environment, and can also chelate with cadmium ions to promote the formation of insoluble precipitates. It is biodegradable and has no secondary pollution.

[0036] 4) The preparation process of the weakly alkaline soil cadmium passivating agent of the present invention is relatively simple, and the formula can be customized to suit different polluted soils. It has broad commercial prospects by expanding the market through multiple channels. Attached Figure Description

[0037] Figure 1 pH value measurement results.

[0038] Figure 2 Results of determination of available cadmium (mg / kg) in soil.

[0039] Figure 3 Determination of cadmium content (mg / kg) in wheat grains. Detailed Implementation

[0040] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0041] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. Unless otherwise specified, the experimental reagents used in the following embodiments are all conventional biochemical reagents; and unless otherwise specified, the experimental methods are all conventional methods.

[0042] Example: Cadmium passivating agent for weakly alkaline soil and its preparation method

[0043]

[0044] The above preparation process is as follows:

[0045] Preparation of S1 mineral complex: Natural sepiolite and calcium-based bentonite were dried in a hot air drying oven at 60-65℃ for 8-10 hours, pulverized, and passed through a 120-mesh standard sieve to remove impurities. Then, they were added to a high-speed mixer and mixed at 300-400 r / min at room temperature for 15-20 minutes. Polyether-polyester diblock copolymer was slowly added and mixed for another 25-30 minutes until homogeneous. The mixture was then transferred to a nitrogen-protected activation furnace and activated at 350-400℃ at 5-8℃ / min for 1.5-2 hours. After cooling to room temperature, the mixture was ground and passed through a 120-mesh sieve to obtain a highly active mineral complex. The complex was then sealed and protected from light for later use.

[0046] Preparation of S2 composite microbial agent: The microbial agent is mixed evenly, the bacterial cells are separated by centrifugation and precipitation, then galactose protectant is added, and the mixture is freeze-dried under vacuum to obtain composite microbial powder;

[0047] Preparation of S3 phosphorus-modified biochar: Peanut shells and corn cobs were mixed at a mass ratio of 1:1, dried at 60℃ for 12 hours, and pulverized through a 100-mesh sieve to obtain biomass raw materials; the biomass raw materials were mixed with a 10% mass concentration potassium dihydrogen phosphate solution at a solid-liquid ratio of 1:3, soaked at 25-35℃ for 8-15 hours, and stirred 2-3 times; the soaked material was filtered and drained, placed in a nitrogen-protected pyrolysis furnace, heated at 10℃ / min to 500-550℃ for pyrolysis for 2.5-3 hours, cooled to room temperature, ground through a 100-mesh sieve, washed with deionized water until neutral, and dried at 60℃ to obtain phosphorus-modified biochar for later use.

[0048] Preparation of S4 bioactive component compound: According to the bioactive component ratio, add phosphorus-modified biochar, lecithin, and phosphatidylserine to a mixer and mix at 250 r / min at room temperature for 20 min. Add the prepared compound microbial powder and stir at ≤25℃ at low speed for 15 min (to avoid high temperature inactivation) until the system is homogeneous to obtain the bioactive complex. Seal and store at low temperature for later use.

[0049] Pretreatment of S5 auxiliary stabilizer: Nano-hydroxyapatite was pulverized and passed through a 120-mesh sieve, and then added to a high-speed mixer in proportion with the chitosan-grafted polyaspartic acid complex. The mixture was mixed at 300 r / min for 15 min to obtain the pretreated auxiliary stabilizer for later use.

[0050] S6 Finished Passivating Agent Molding: Homogenization: Add the mineral complex, bioactive complex, and auxiliary stabilizer to a double helix conical mixer according to the weight ratio, and mix at 150~200r / min for 30~40min at a low temperature of ≤28℃ until all components are evenly dispersed and free of lumps; grind the mixture through a 100-mesh standard sieve to remove coarse particle impurities, and the finished weakly alkaline soil cadmium passivating agent is obtained.

[0051] Comparative Example: Cadmium Passivating Agent for Weakly Alkaline Soils and Its Preparation Method

[0052]

[0053] The symbol “ / ” indicates the presence of this substance; the amount of “carboxymethyl cellulose” used is the sum of the amounts of lecithin and phosphatidylserine.

[0054] The dosages of Comparative Examples 1-4 were the same as those in Example 1, and the experiments were conducted using a single-factor variable.

[0055] Comparative Example 5: Soil passivating agent prepared according to CN 106424115 A.

[0056] Comparative Example 6: Soil passivating agent prepared according to CN 114015451A.

[0057] Comparative Example 7: Soil passivating agent prepared according to CN 120679824 A.

[0058] Comparative Example 8: Soil passivating agent prepared according to CN 120737852.

[0059] Test Example 1: The effect of the weakly alkaline soil cadmium passivating agent of the present invention on cadmium pollution.

[0060] 1. Experimental Methods

[0061] In this embodiment, soil from the vicinity of a certain enterprise was used as the cadmium-contaminated soil for testing. The soil pH was 8.30, and the total cadmium concentration was 3.51 mg / kg.

[0062] The total cadmium and total lead contents in the soil samples were determined by graphite furnace atomic absorption spectrophotometry according to the standard "Determination of Lead and Cadmium in Soil Quality" (GB / T 17141-1997). The available cadmium in the soil was determined by atomic absorption spectrophotometry according to the standard "Determination of Available Lead and Cadmium in Soil Quality" (GB / T 23739-2009).

[0063] Twelve treatments were established using indoor soil culture: a control group, Examples 1-3, and Comparative Examples 1-8. Each treatment had five replicates, and the plants were passivated for 21 days. Twenty wheat seeds were sown into each pot in the blank control group and each example group, and wheat was managed according to standard wheat cultivation procedures.

[0064] 2. Determination of available cadmium content in soil

[0065] Weigh 5g of passivated soil sample into a 100mL Erlenmeyer flask, add 25mL of diethylenetriaminepentaacetic acid (DTA) extractant, seal with plastic wrap and a rubber band, and place on a horizontal reciprocating shaker. Shake for 3 hours at 23-27℃ and 160-200 rpm. After extraction, allow to stand and filter, discarding 2-3mL of the initial filtrate. Determine the available cadmium content of the remaining filtrate using an atomic emission spectrophotometer with acetylene as the carrier gas flame.

[0066] After the wheat matured, the cadmium content in the wheat grains of potted wheat was measured, and the pH value and available cadmium content of the potted soil were also measured.

[0067] 3. Data Processing

[0068] Data processing was performed using Graphpad Prism 7.0 software, and the measurement data was presented in the following format: This indicates that one-way ANOVA was used for comparisons among multiple groups, and pairwise comparisons between groups were performed using SNK-q, with P < 0.05 considered statistically significant.

[0069] 4. Measurement Results

[0070] 1) pH measurement results are as follows Figure 1 As shown in Table 1:

[0071] Table 1. Changes in pH value in each example.

[0072]

[0073] Table 1 and Figure 1 It can be seen that Tukey's multiple comparison results and Figure 1 It is evident that the pH values ​​of Examples 1-3 differed significantly from those of the comparative examples (Comparative Examples 1, 4-8). Among them, Example 1 had the largest absolute Mean Diff. values ​​(0.084-0.164), significantly higher than those of Example 2 (0.060-0.140) and Example 3 (0.056-0.136), indicating that Example 1 provided better pH control and could more accurately maintain the pH of slightly alkaline soil within a suitable range.

[0074] 2) Results of the determination of available cadmium in the soil (mg / kg) are as follows: Figure 2 As shown in Table 2:

[0075]

[0076] Results of soil available cadmium determination ( Figure 2Table 2 further corroborates the superior effects of the embodiments: The soil available cadmium content of Embodiment 1 is significantly or extremely significantly different from that of all comparative examples, and its absolute value is generally higher than that of Embodiment 2 (-0.003400~-0.0356) and Embodiment 3 (-0.006000~-0.0382), with the largest difference from Comparative Example 3, indicating that Embodiment 1 has the most significant effect in reducing soil available cadmium; Embodiments 2 and 3 have no significant difference (ns) from some comparative examples (such as Comparative Examples 6 and 7), while Embodiment 1 does not have this situation, indicating that Embodiment 1 has a more stable and comprehensive effect in reducing soil available cadmium, showing a core advantage in cadmium-contaminated soil remediation.

[0077] 3) The results of the determination of cadmium content (mg / kg) in wheat grains are as follows: Figure 3 As shown in Table 3:

[0078] Table 3. Results of Cadmium Content (mg / kg) in Wheat Grains

[0079]

[0080] From Table 3 and Figure 3 As can be seen from the Tukey multiple comparison test analysis of the wheat grain cadmium content determination results, the cadmium content of Examples 1-3 was significantly lower than that of all comparative examples, demonstrating excellent cadmium reduction technology. Among them, Example 1 showed the most outstanding performance, with an average difference of -0.0494 mg / kg (95% confidence interval: -0.06144 to -0.03736) compared with Examples 2 and 3, indicating that the cadmium content control effect of Example 1 in wheat grains was significantly better than that of Examples 2, 3 and all comparative examples, demonstrating a clear overall technical advantage.

[0081] The above descriptions are merely embodiments of the present invention, and common knowledge such as specific technical solutions and / or characteristics are not described in detail here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the technical solutions of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the implementation of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A weakly alkaline soil cadmium passivating agent, characterized in that, The weakly alkaline soil cadmium passivating agent mainly comprises the following components by weight: 30-50 parts of mineral complex, 40-60 parts of biologically active component, and 5-15 parts of auxiliary stabilizer; wherein, the mineral complex includes natural sepiolite, calcium-based bentonite, and polyether-polyester diblock copolymer; the biologically active component includes microbial inoculant, phosphorus-modified biochar, lecithin, and phosphatidylserine; the auxiliary stabilizer includes nano-hydroxyapatite and chitosan-grafted polyaspartic acid complex; the microbial inoculant is a compound inoculant composed of Bacillus subtilis, Bacillus amyloliquefaciens, Bacillus thuringiensis, and Pseudomonas nitroreductoides.

2. The weakly alkaline soil cadmium passivating agent according to claim 1, characterized in that, The main components, by weight, are as follows: 20-30 parts of natural sepiolite, 8-12 parts of calcium-based bentonite, 2-8 parts of polyether-polyester diblock copolymer, 8-12 parts of microbial inoculant, 26-35 parts of phosphorus-modified biochar, 6-10 parts of lecithin, 1-3 parts of phosphatidylserine, 4-12 parts of nano-hydroxyapatite, and 1-3 parts of chitosan-grafted polyaspartic acid complex; more preferably, the components are: 25 parts of natural sepiolite, 10 parts of calcium-based bentonite, 5 parts of polyether-polyester diblock copolymer, 10 parts of microbial inoculant, 30 parts of phosphorus-modified biochar, 8 parts of lecithin, 2 parts of phosphatidylserine, 8 parts of nano-hydroxyapatite, and 2 parts of chitosan-grafted polyaspartic acid complex.

3. The weakly alkaline soil cadmium passivating agent according to claim 1, characterized in that, The polyether-polyester diblock copolymer is one or more of the following: polyethylene glycol-polylactide, polyethylene glycol monomethyl ether-polylactide, polyethylene glycol-polylactide-lactide, polyethylene glycol-polycaprolactone, polyethylene glycol-polyorthoester, polypropylene glycol-polylactide, or polybutanediol-polylactide; preferably, the polyether-polyester diblock copolymer is polyethylene glycol 2000-polylactide 2000 or polyethylene glycol monomethyl ether 2000-polylactide 2000.

4. The weakly alkaline soil cadmium passivating agent according to claim 1, characterized in that, The microbial agent contains Bacillus subtilis, Bacillus amyloliquefaciens, Bacillus thuringiensis, and Pseudomonas nitroreductoids in a microbial mass ratio of 2-4:4-6:1-3:0.5-1, and the effective viable count of each of the Bacillus subtilis, Bacillus amyloliquefaciens, Bacillus thuringiensis, and Pseudomonas nitroreductoids is ≥1.0 × 10⁻⁶. 9 cfu·g -1 The effective viable count of the compound microbial agent is ≥5.0×10⁻⁶. 9 cfu·g -1 Further preferably, the microbial mass ratio of Bacillus subtilis, Bacillus amyloliquefaciens, Bacillus thuringiensis, and Pseudomonas nitroreductoids is 3:5:2:

1.

5. The weakly alkaline soil cadmium passivating agent according to claim 1, characterized in that, The main components by weight are as follows: 25 parts of natural sepiolite, 10 parts of calcium-based bentonite, 5 parts of polyethylene glycol 2000-polylactide 2000 or polyethylene glycol monomethyl ether 2000-polylactide 2000, 10 parts of microbial inoculant, 30 parts of phosphorus-modified biochar, 8 parts of lecithin, 2 parts of phosphatidylserine, 8 parts of nano-hydroxyapatite, and 2 parts of chitosan-grafted polyaspartic acid complex; the microbial inoculant is composed of Bacillus subtilis, Bacillus amyloliquefaciens, Bacillus thuringiensis, and Pseudomonas nitroreductoids in a microbial mass ratio of 3:5:2:

1.

6. The weakly alkaline soil cadmium passivating agent according to claim 1, characterized in that, The preparation method of polyethylene glycol 2000-polylactide 2000 is as follows: Polyethylene glycol 2000 is added to a polymerization flask, kept warm and stirred, and vacuumed to remove water. Stannous octoate / toluene solution is added, stirred and dispersed, kept warm and stirred, and vacuumed to remove toluene. Polylactide 2000 is then added, and the reaction is carried out while keeping warm and stirring. After the reaction is complete, the temperature is lowered, an organic solvent is added and stirred to dissolve, a metal remover is added for treatment, and the mixture is filtered. The filtrate is added to anhydrous diethyl ether to dissolve and crystallize. After further dissolution, the mixture is filtered through a PTFE membrane. The filtrate is added to anhydrous diethyl ether to crystallize, filtered, and the filter cake is dried to obtain a polyethylene glycol 2000-polylactide 2000 diblock copolymer.

7. The weakly alkaline soil cadmium passivating agent according to claim 1, characterized in that, The preparation method is as follows: Preparation of S1 mineral complex: Natural sepiolite and calcium-based bentonite were dried, pulverized, sieved to remove impurities, mixed evenly, and polyether-polyester diblock copolymer was added and mixed further; the mixture was heated and activated under inert gas protection, cooled, ground and sieved to obtain a highly active mineral complex, which was sealed and protected from light for later use. Preparation of S2 composite microbial inoculant: Mix multiple microbial inoculants evenly, enrich the bacterial cells by centrifugation, add a protectant and freeze-dry under vacuum to obtain composite microbial powder; Preparation of S3 phosphorus-modified biochar: Peanut shells and corn cobs are mixed, dried, crushed and sieved to obtain biomass raw materials; the biomass raw materials are mixed with phosphorus source solution, soaked and stirred, filtered and drained, pyrolyzed under inert gas protection, cooled, ground and sieved, washed until neutral and then dried to obtain phosphorus-modified biochar for later use. S4 Bioactive Component Compound: Mix phosphorus-modified biochar, lecithin, and phosphatidylserine evenly according to the formula, add compound microbial powder, and stir and mix evenly at low temperature to obtain a bioactive complex. Seal and store at low temperature for later use. S5 auxiliary stabilizer pretreatment: After crushing and sieving nano hydroxyapatite, it is mixed evenly with chitosan-grafted polyaspartic acid complex according to the ratio to obtain pretreated auxiliary stabilizer for later use. S6 Finished Product Molding: The mineral complex, bioactive complex, and auxiliary stabilizer are added to the mixing equipment according to the weight parts, and mixed at low temperature until uniform and free of lumps. After grinding and sieving to remove coarse particles, the finished product is obtained.

8. A weakly alkaline soil cadmium passivating agent, characterized in that, The weakly alkaline soil cadmium passivating agent mainly comprises the following components by weight: 40 parts mineral complex, 50 parts bioactive component, and 10 parts auxiliary stabilizer; wherein, the mineral complex includes natural sepiolite, calcium-based bentonite, and polyethylene glycol 2000-polylactide 2000 diblock copolymer; the bioactive component includes microbial inoculants, phosphorus-modified biochar, lecithin, and phosphatidylserine; the auxiliary stabilizer includes nano-hydroxyapatite and chitosan-grafted polyaspartic acid complex; the microbial inoculants are Bacillus subtilis, Bacillus amyloliquefaciens, and Bacillus thuringiensis. A compound microbial agent composed of Bacillus aureus and Pseudomonas nitroreductoids; wherein the composition includes 25 parts of natural sepiolite, 10 parts of calcium-based bentonite, 5 parts of polyethylene glycol 2000-polylactide 2000 diblock copolymer, 10 parts of microbial agent, 30 parts of phosphorus-modified biochar, 8 parts of lecithin, 2 parts of phosphatidylserine, 8 parts of nano-hydroxyapatite, and 2 parts of chitosan-grafted polyaspartic acid complex; wherein the microbial agent is composed of Bacillus subtilis, Bacillus amyloliquefaciens, Bacillus thuringiensis, and Pseudomonas nitroreductoids in a microbial mass ratio of 3:5:2:

1.

9. The application of the weakly alkaline soil cadmium passivating agent according to claim 8 in the in-situ remediation of soil heavy metal pollution, wherein the heavy metal pollution is cadmium pollution.

10. The application of the weakly alkaline soil cadmium passivating agent according to claim 8 in in-situ remediation of heavy metal pollution in soil, characterized in that, The weakly alkaline soil cadmium passivating agent is applied to heavy metal contaminated soil and then tilled; the application rate of the weakly alkaline soil cadmium passivating agent is 0.5%-1.8% of the weight of the potted soil; when the application environment is a field, the application rate of the weakly alkaline soil cadmium passivating agent is 100-200 kg / mu.

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