Heavy metal contaminated soil passivation remediation conditioner and application thereof

Abstract

The invention discloses a heavy metal contaminated soil passivation remediation conditioner and application thereof, and belongs to the technical field of soil remediation. According to the conditioner, shaddock peel activated carbon serves as a carrier, a porous structure is constructed through phosphoric acid activation, then ammonium phosphomolybdate nano-clusters are loaded, a polycaprolactone cross-linked network is constructed through click chemistry to achieve stable anchoring of active components, and the dispersity of the material is enhanced in combination with a zwitterionic functional modification process. During application, the conditioner, potassium feldspar powder, a calcium magnesium phosphate fertilizer, a microbial agent and other components are compounded and applied to form a multi-level adsorption-chelation system, continuous fixation of heavy metals is achieved through the synergistic effect of ion exchange, coordination chelation and electrostatic adsorption, and meanwhile the soil micro-ecology is improved. The prepared remediation agent has the stability of a three-dimensional cross-linked network structure and the zwitter-ion hydrated dispersion characteristic, the heavy metal passivation efficiency can be remarkably improved, the remediation agent has the slow-release effect and the anti-scouring performance, and the synergistic interaction of soil remediation and fertility improvement is achieved.

Description

Technical Field

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

[0002] For various types of soil degradation and pollution, the academic community generally believes that building multifunctional soil remediation systems is key to improving farmland quality. Biomass-based soil conditioners, due to their environmental friendliness and resource recycling properties, have become a key research area in soil remediation.

[0003] Soil conditioners primarily improve soil quality by improving soil physical, chemical, and biological properties. In terms of physical properties, conditioners can significantly improve the three-phase ratio of soil, enhance water infiltration rate, and water holding capacity by regulating pore structure, reducing bulk density, and promoting the formation of aggregate structure. Studies have shown that an appropriate pore distribution can increase soil aeration porosity, which is directly related to root respiration and nutrient absorption efficiency. In terms of chemical properties, conditioners regulate soil pH through proton exchange and coordination, promote the formation of organic-inorganic complexes, and improve soil fertility retention. In terms of biological properties, conditioners can increase the number of microorganisms, promote organic matter transformation, nutrient recycling, and bioremediation, increase soil enzyme activity, and accelerate the transformation of heavy metal forms and the degradation of organic pollutants.

[0004] Chinese invention patent application number CN201710700630.3 discloses a heavy metal-contaminated soil conditioner prepared by chelating humic acid, 1,3,5-triazine-2,4,6-trisulfide, nitrogen fertilizer, phosphate fertilizer, and potassium fertilizer. The conditioner includes humate, 1,3,5-triazine-2,4,6-trisulfide, nitrogen, phosphorus pentoxide, and potassium oxide. However, this invention simply mixes the components without establishing chemical bonds between them. Mechanical mixing causes the material to easily separate in the soil solution, resulting in uneven distribution of the active components. Summary of the Invention

[0005] In response to the above situation, in order to overcome the defects of the existing technology, the present invention constructs a polycaprolactone cross-linked network through click chemistry, stably anchors ammonium phosphomolybdate in the pore structure of biochar, utilizes the hydration effect of phosphorylcholine groups to enhance the dispersion stability of the material in the soil, and forms a dynamic passivation barrier through the synergistic action of multiple components to achieve continuous fixation of heavy metals and soil microecological restoration.

[0006] In order to achieve the above objectives, the following technical solutions are adopted: On the one hand, the present invention provides a heavy metal contaminated soil passivation remediation conditioner, which is prepared by the following steps: S1. Grind grapefruit peel into a particle size of 1-3 mm, heat to 500-520° C. at 10° C. / min under a nitrogen atmosphere and carbonize for 3 h, then immerse in a 20% mass concentration phosphoric acid solution, activate in a constant temperature water bath at 80° C. for 4 h, wash until neutral, and then dry in an oven at 105° C. for 12-18 h to obtain grapefruit peel activated carbon; S2, immersing the grapefruit peel activated carbon obtained in step S1 in a first mixed solution consisting of 0.2 mol / L ammonium molybdate and 0.1 mol / L sodium dihydrogen phosphate, adjusting the pH to 4.5, and reacting at 80° C. with stirring for 8 h. After the reaction is completed, centrifuging at 3000 rpm for 10 min, washing with deionized water three times, and vacuum drying at 80° C. for 6 h to obtain activated grapefruit peel activated carbon with ammonium phosphomolybdate loaded on its surface; S3, using stannous isooctanoate as a catalyst, ring-opening polymerizing caprolactone monomer at 120° C. for 24 hours under nitrogen protection to generate hydroxyl-terminated polycaprolactone, reacting the hydroxyl-terminated polycaprolactone with sodium azide in DMF at 60° C. for 24 hours to generate double-end azide-terminated polycaprolactone, and reacting the activated grapefruit peel activated carbon obtained in step S2 with a silane coupling agent in toluene at 60° C. for 12-18 hours, centrifuging and separating, and drying at 60-80° C. for 12-24 hours to obtain cross-linked modified activated carbon; S4, adding the cross-linked modified activated carbon obtained in step S3 and NO2A-butyne-di-tert-butyl ester to a 30% by mass DMF solution, and then adding the mixture to a second mixed solution consisting of 0.1 mol / L copper sulfate and 0.2 mol / L ascorbic acid, stirring at 40°C for 16 hours, filtering, washing, and drying to obtain a functionalized activated carbon composite material; S5. Add the product obtained in step S4 to a dichloromethane solution containing 5% trifluoroacetic acid, react at room temperature for 3 h to remove the tert-butyl ester protecting group, wash to neutrality after centrifugation, and dry to obtain a deprotected product. Disperse the deprotected product and 2-methacryloyloxyethyl phosphorylcholine in a phosphate buffer solution at pH 6.8, and ultrasonically treat at a power of 200 W and a frequency of 40 kHz for 30-60 min. Then, freeze-dry at -50°C for 48 h to obtain a finished conditioner.

[0007] Furthermore, in step S1, the feeding ratio of pomelo peel to phosphoric acid solution is 1 g: 3-6 mL.

[0008] Furthermore, in step S2, the feeding ratio of the pomelo peel activated carbon to the first mixed solution is 1 g: 8-12 mL.

[0009] Furthermore, in step S3, the molar ratio of stannous isooctanoate to caprolactone monomer is 1:80-120.

[0010] Furthermore, in step S3, the molecular weight range of the hydroxyl-terminated polycaprolactone is 5000-20000 Da, and the feeding ratio of the hydroxyl-terminated polycaprolactone, sodium azide and DMF is 1 g: 0.004-0.02 g: 20-40 mL.

[0011] Furthermore, in step S3, the feed ratio of activated grapefruit peel activated carbon, silane coupling agent and toluene is 1 g: 0.1-0.3 g: 10-20 mL, and the silane coupling agent is one or more of KH-550, KH-560 and KH-570.

[0012] Furthermore, in step S4, the feed ratio of the cross-linked modified activated carbon, NO2A-butyne-di-tert-butyl ester, DMF solution, and the second mixed solution is 1 g: 0.3-0.7 g: 15-25 mL: 20-40 mL.

[0013] Furthermore, in step S5, the feeding ratio of the functionalized activated carbon composite material and the dichloromethane solution of trifluoroacetic acid is 1 g: 30-70 mL, and the feeding ratio of the deprotected product, 2-methacryloyloxyethyl phosphorylcholine and phosphate buffer in step S5 is 1 g: 1-3 g: 20-40 mL.

[0014] On the other hand, the present invention also provides an application of a conditioner for passivating and remediating heavy metal contaminated soil: by weight, 20-30 parts of the conditioner are uniformly mixed with 5-10 parts of potassium feldspar powder, 10-15 parts of calcium magnesium phosphate fertilizer, 15-25 parts of agricultural lime, 20-30 parts of humic acid, and 0.5-2 parts of microbial agent, and the heavy metal contaminated soil is passivated and remediated at an application rate of 3000 kg / hectare.

[0015] Furthermore, the microbial agent includes Bacillus amyloliquefaciens, Bacillus subtilis, Aspergillus niger, Pseudomonas aeruginosa, and Streptomyces tenuifolius. The number of viable bacteria of Bacillus amyloliquefaciens is ≥1×10^8 CFU / g, the number of viable bacteria of Bacillus subtilis is ≥5×10^7 CFU / g, the number of viable bacteria of Aspergillus niger is ≥2×10^7 CFU / g, the number of viable bacteria of Pseudomonas aeruginosa is ≥2×10^7 CFU / g, and the number of viable bacteria of Streptomyces tenuifolius is ≥1×10^8 CFU / g.

[0016] The beneficial effects of the present invention are: (1) The conditioner prepared by the present invention can passivate and repair heavy metals in the soil, improve the soil microenvironment, and enhance biodiversity. Through the composite loading of grapefruit peel activated carbon and ammonium phosphomolybdate, combined with the cross-linked network structure of polycaprolactone and the functionalization of phosphorylcholine zwitterion, a multi-level adsorption chelation system is formed, wherein ammonium phosphomolybdate fixes heavy metals through ion exchange, triazacyclononane groups form a stable coordination structure with heavy metals, and phosphorylcholine groups further adsorb heavy metal ions through electrostatic action. The conditioner is used as a fertilizer in combination with potassium feldspar powder, calcium magnesium phosphate fertilizer, agricultural lime, humic acid, and microbial agents, which can increase soil permeability and improve soil fertility. (2) Activated carbon was prepared from pomelo peel biomass. A porous structure with high specific surface area was formed through phosphoric acid activation to achieve resource utilization. Ammonium phosphomolybdate was evenly loaded, which significantly improved the selective adsorption capacity of activated carbon for heavy metals. The polyoxometalate structure of ammonium phosphomolybdate remained stable under acidic conditions. Its molybdenum-oxygen tetrahedron had a specific coordination effect with heavy metal ions. Through the click reaction between the double-terminal azide group of polycaprolactone and the alkyne group, a three-dimensional cross-linked network was constructed on the surface of the activated carbon, which not only enhanced the mechanical strength of the material but also prevented the loss of active components. Polycaprolactone is a degradable polymer material. Its slow degradation characteristics give the conditioner a sustained-release effect. (3) The triazacyclononane of NO2A-butyne-di-tert-butyl ester serves as the core structure of the macrocyclic ligand. This matrix can catalyze the cycloaddition reaction between the butyne group and the double-terminal azide group of polycaprolactone to form a stable triazole ring cross-linked network. On the one hand, it improves the overall chelating strength, and on the other hand, it significantly improves the mechanical strength and anti-scouring properties of the material. The triazacyclononane also has a strong chelating effect. Through metal coordination, the triazacyclononane can be used as a Lewis acid catalyst to promote the precipitation reaction of heavy metal ions and acid radical ions. (4) After the tert-butyl ester protecting group in NO2A-butyne-di-tert-butyl ester is removed, the exposed carboxylic acid group is introduced into 2-methacryloyloxyethyl phosphorylcholine through covalent bonding, hydrogen bonding and other bonding methods. 2-methacryloyloxyethyl phosphorylcholine has zwitterionic properties. The phosphorylcholine groups on it form a dense hydration layer through hydration, which significantly reduces the surface tension of soil particles, allowing the conditioner to quickly absorb water and swell in the soil, forming hydrophilic channels, promoting the penetration of water and nutrients, reducing the risk of runoff and heavy metal loss with soil and water, and reducing the van der Waals force between the conditioner particles to prevent the formation of agglomerates. This component is decomposed by the phosphatase produced by microorganisms to release phosphate, and the organic acid is secreted by the synergistic action of microbial agents and humic acid to dissolve heavy metals, and cooperates with the phosphorus source in calcium magnesium phosphate fertilizer to achieve long-term fixation of heavy metals. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1The present invention is a flow chart for preparing a heavy metal contaminated soil passivation and remediation conditioner.

[0018] The accompanying drawings are used to provide further understanding of the present invention and constitute a part of the specification. They are used to explain the present invention together with the embodiments of the present invention and do not constitute a limitation of the present invention. DETAILED DESCRIPTION

[0019] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0020] Unless otherwise defined, all technical and scientific terms used herein have the same meanings as those familiar to those skilled in the art. Furthermore, any methods and materials similar or equivalent to those described herein can be applied to the present invention. The preferred embodiments and materials described herein are for illustrative purposes only and are not intended to limit the scope of this application.

[0021] The experimental methods in the following examples are conventional methods unless otherwise specified. The experimental materials used in the following examples are purchased from commercial channels unless otherwise specified. Figure 1 .

[0022] Among them, Bacillus amyloliquefaciens, strain number CICC 10035, was purchased from Beijing Center for Biological Collection.

[0023] Bacillus subtilis, strain number CICC 25064, was purchased from Beijing Center for Biological Collection.

[0024] Aspergillus niger, strain number CICC 2243, was purchased from Beijing Center for Biological Collection.

[0025] Pseudomonas aeruginosa, strain number CICC 10204, was purchased from Beijing Biorepository Center.

[0026] Streptomyces tenuifolius, strain number CICC 11006, was purchased from Beijing Center for Biological Collection.

[0027] Example 1: A heavy metal contaminated soil passivation and remediation conditioner and its application, the conditioner is prepared by the following steps: S1. 1 g of grapefruit peel was crushed into a particle size of 1 mm, heated to 500°C at 10°C / min under a nitrogen atmosphere for carbonization for 3 h, then immersed in 3 mL of 20% mass concentration phosphoric acid solution, activated in a constant temperature water bath at 80°C for 4 h, washed until neutral, and then dried in an oven at 105°C for 12 h to obtain grapefruit peel activated carbon; S2, immersing 1 g of the grapefruit peel activated carbon obtained in step S1 into 8 mL of a first mixed solution consisting of 0.2 mol / L ammonium molybdate and 0.1 mol / L sodium dihydrogen phosphate, adjusting the pH to 4.5, and reacting at 80° C. with stirring for 8 h. After the reaction is completed, centrifuging at 3000 rpm for 10 min, washing with deionized water three times, and vacuum drying at 80° C. for 6 h to obtain activated grapefruit peel activated carbon with ammonium phosphomolybdate loaded on its surface; S3, according to the molar ratio of stannous isooctanoate to caprolactone monomer of 1:80, using stannous isooctanoate as a catalyst, the caprolactone monomer was ring-opening polymerized at 120°C for 24 hours under nitrogen protection to generate a hydroxyl-terminated polycaprolactone with a molecular weight range of 5000-20000 Da, 1g of the hydroxyl-terminated polycaprolactone was reacted with 0.004g of sodium azide in 20mL of DMF at 60°C for 24h to generate a double-ended azide-terminated polycaprolactone, 1g of the activated grapefruit peel activated carbon obtained in step S2 was reacted with 0.1g of silane coupling agent KH-550 in 10mL of toluene at 60°C for 12h with stirring, the mixture was separated after centrifugation and dried at 60°C for 12h to obtain a cross-linked modified activated carbon; S4, adding 1 g of the cross-linked modified activated carbon obtained in step S3 and 0.3 g of NO2A-butyne-di-tert-butyl ester to 15 mL of a 30% mass fraction DMF solution, and then adding the mixture to 20 mL of a second mixed solution consisting of 0.1 mol / L copper sulfate and 0.2 mol / L ascorbic acid, stirring at 40°C for 16 h, filtering, washing, and drying to obtain a functionalized activated carbon composite material; S5. Add 1 g of the product obtained in step S4 to 30 mL of a dichloromethane solution containing 5% trifluoroacetic acid, react at room temperature for 3 h to remove the tert-butyl ester protecting group, wash until neutral after centrifugation, and dry to obtain a deprotected product. Disperse 1 g of the deprotected product and 1 g of 2-methacryloyloxyethyl phosphorylcholine in 20 mL of pH 6.8 phosphate buffer, ultrasonically treat at a power of 200 W and a frequency of 40 kHz for 30 min, and then freeze-dry at -50°C for 48 h to obtain a finished conditioner.

[0028] The application is as follows: by weight, 20 parts of the conditioner are evenly mixed with 5 parts of potassium feldspar powder, 10 parts of calcium magnesium phosphate fertilizer, 15 parts of agricultural lime, 20 parts of humic acid, and 0.5 parts of microbial agent, and the heavy metal contaminated soil is passivated and repaired at an application rate of 3000 kg / hectare.

[0029] The microbial agent includes Bacillus amyloliquefaciens, Bacillus subtilis, Aspergillus niger, Pseudomonas aeruginosa, and Streptomyces tenuifolius. The number of viable bacteria of Bacillus amyloliquefaciens is ≥1×10^8 CFU / g, the number of viable bacteria of Bacillus subtilis is ≥5×10^7 CFU / g, the number of viable bacteria of Aspergillus niger is ≥2×10^7 CFU / g, the number of viable bacteria of Pseudomonas aeruginosa is ≥2×10^7 CFU / g, and the number of viable bacteria of Streptomyces tenuifolius is ≥1×10^8 CFU / g.

[0030] Example 2: A heavy metal contaminated soil passivation and remediation conditioner and its application, the conditioner is prepared by the following steps: S1. 1 g of grapefruit peel was crushed to a particle size of 3 mm, heated to 520°C at 10°C / min under a nitrogen atmosphere for carbonization for 3 h, then immersed in 6 mL of 20% phosphoric acid solution, activated in a constant temperature water bath at 80°C for 4 h, washed until neutral, and then dried in an oven at 105°C for 18 h to obtain grapefruit peel activated carbon; S2, immersing 1 g of the grapefruit peel activated carbon obtained in step S1 into 12 mL of a first mixed solution consisting of 0.2 mol / L ammonium molybdate and 0.1 mol / L sodium dihydrogen phosphate, adjusting the pH to 4.5, and reacting at 80° C. with stirring for 8 h. After the reaction is completed, centrifuging at 3000 rpm for 10 min, washing with deionized water three times, and vacuum drying at 80° C. for 6 h to obtain activated grapefruit peel activated carbon with ammonium phosphomolybdate loaded on its surface; S3, according to the molar ratio of stannous isooctoate to caprolactone monomer of 1:120, using stannous isooctoate as a catalyst, the caprolactone monomer was ring-opening polymerized at 120°C for 24 hours under nitrogen protection to generate a hydroxyl-terminated polycaprolactone with a molecular weight range of 5000-20000 Da, 1g of the hydroxyl-terminated polycaprolactone was reacted with 0.02g of sodium azide in 40mL of DMF at 60°C for 24h to generate a double-ended azide-terminated polycaprolactone, 1g of the activated grapefruit peel activated carbon obtained in step S2 and 0.3g of a silane coupling agent composed of KH-550 and KH-560 in a mass ratio of 1:1 were stirred in 20mL of toluene at 60°C for 18h, separated by centrifugation, and dried at 80°C for 24h to obtain a cross-linked modified activated carbon; S4, adding 1 g of the cross-linked modified activated carbon obtained in step S3 and 0.7 g of NO2A-butyne-di-tert-butyl ester to 25 mL of a 30% mass fraction DMF solution, then adding the mixture to 40 mL of a second mixed solution consisting of 0.1 mol / L copper sulfate and 0.2 mol / L ascorbic acid, stirring at 40°C for 16 h, filtering, washing, and drying to obtain a functionalized activated carbon composite material; S5. Add 1 g of the product obtained in step S4 to 70 mL of a dichloromethane solution containing 5% trifluoroacetic acid, react at room temperature for 3 h to remove the tert-butyl ester protecting group, wash until neutral after centrifugation, and dry to obtain a deprotected product. Disperse 1 g of the deprotected product and 3 g of 2-methacryloyloxyethyl phosphorylcholine in 40 mL of pH 6.8 phosphate buffer, ultrasonically treat at a power of 200 W and a frequency of 40 kHz for 60 min, and then freeze-dry at -50°C for 48 h to obtain a finished conditioner.

[0031] The application is as follows: by weight, 30 parts of the conditioner are evenly mixed with 10 parts of potassium feldspar powder, 15 parts of calcium magnesium phosphate fertilizer, 25 parts of agricultural lime, 30 parts of humic acid, and 2 parts of microbial agent, and the heavy metal contaminated soil is passivated and repaired at an application rate of 3000 kg / hectare.

[0032] The components included in the microbial agent and the number of viable bacteria in each component are the same as those in Example 1.

[0033] Example 3: A heavy metal contaminated soil passivation and remediation conditioner and its application, the conditioner is prepared by the following steps: S1. 1 g of grapefruit peel was crushed to a particle size of 2 mm, heated to 510°C at 10°C / min under a nitrogen atmosphere for carbonization for 3 h, then immersed in 4 mL of 20% phosphoric acid solution, activated in a constant temperature water bath at 80°C for 4 h, washed until neutral, and then dried in an oven at 105°C for 15 h to obtain grapefruit peel activated carbon; S2, immersing 1 g of the grapefruit peel activated carbon obtained in step S1 into 10 mL of a first mixed solution consisting of 0.2 mol / L ammonium molybdate and 0.1 mol / L sodium dihydrogen phosphate, adjusting the pH to 4.5, and reacting at 80° C. with stirring for 8 h. After the reaction is completed, centrifuging at 3000 rpm for 10 min, washing with deionized water three times, and vacuum drying at 80° C. for 6 h to obtain activated grapefruit peel activated carbon with ammonium phosphomolybdate loaded on its surface; S3, according to the molar ratio of stannous isooctoate to caprolactone monomer is 1:100, using stannous isooctoate as a catalyst, the caprolactone monomer is ring-opening polymerized at 120°C for 24 hours under nitrogen protection to generate a hydroxyl-terminated polycaprolactone with a molecular weight range of 5000-20000Da, 1g of hydroxyl-terminated polycaprolactone is reacted with 0.012g of sodium azide in 30mL of DMF at 60°C for 24h to generate double-ended azide-terminated polycaprolactone, 1g of the activated grapefruit peel activated carbon obtained in step S2 and 0.2g of a silane coupling agent composed of KH-560 and KH-570 in a mass ratio of 1:1 are stirred and reacted in 15mL of toluene at 60°C for 15h, separated after centrifugation and dried at 70°C for 18h to obtain a cross-linked modified activated carbon; S4, adding 1 g of the cross-linked modified activated carbon obtained in step S3 and 0.5 g of NO2A-butyne-di-tert-butyl ester to 20 mL of a 30% mass fraction DMF solution, then adding the mixture to 30 mL of a second mixed solution consisting of 0.1 mol / L copper sulfate and 0.2 mol / L ascorbic acid, stirring at 40°C for 16 h, filtering, washing, and drying to obtain a functionalized activated carbon composite material; S5. Add 1 g of the product obtained in step S4 to 50 mL of a dichloromethane solution containing 5% trifluoroacetic acid, react at room temperature for 3 h to remove the tert-butyl ester protecting group, wash until neutral after centrifugation, and dry to obtain a deprotected product. Disperse 1 g of the deprotected product and 2 g of 2-methacryloyloxyethyl phosphorylcholine in 30 mL of pH 6.8 phosphate buffer, ultrasonically treat at a power of 200 W and a frequency of 40 kHz for 45 min, and then freeze-dry at -50°C for 48 h to obtain a finished conditioner.

[0034] The application is as follows: according to weight, 25 parts of conditioner are evenly mixed with 7 parts of potassium feldspar powder, 12 parts of calcium magnesium phosphate fertilizer, 20 parts of agricultural lime, 25 parts of humic acid, and 1 part of microbial agent, and the heavy metal contaminated soil is passivated and repaired at an application rate of 3000 kg / hectare.

[0035] The components included in the microbial agent and the number of viable bacteria in each component are the same as those in Example 1.

[0036] Comparative Example 1: In this comparative example, the ammonium phosphomolybdate loading step (ie, step S2) was omitted, and the grapefruit peel activated carbon was directly used to obtain the activated grapefruit peel activated carbon in step S3. The rest was the same as in Example 3.

[0037] Comparative Example 2: In this comparative example, the polycaprolactone cross-linking network construction step (ie, steps S3-S4) was omitted, and the activated carbon loaded with ammonium phosphomolybdate was directly mixed with phosphorylcholine. The rest was the same as in Example 3.

[0038] Comparative Example 3: In this comparative example, the deprotected product was not reacted with 2-methacryloyloxyethyl phosphorylcholine after preparation, and the rest was the same as Example 3.

[0039] Result analysis: The conditioners prepared in Examples 1-3 and Comparative Examples 1-3 were used to passivate and repair the soil, and then the physical and chemical properties were tested. The test results are shown in Table 1.

[0040] The soil passivation remediation process is: (1) Take the soil from the farmland contaminated by heavy metals, remove the surface debris, plow to a depth of 20 cm, break the soil into pieces with a particle size of less than 5 mm, mix them evenly, and divide them into experimental plots. Each plot has an area of 50 m × 50 m. (2) Mix the mixture with potassium feldspar powder, calcium magnesium phosphate fertilizer, agricultural lime, humic acid, and microbial agent in the corresponding weight ratio, apply 3000 kg / hectare, and evenly spread the mixed materials on the soil surface. Use a rotary tiller to plow the soil twice to a depth of 20 cm to fully mix the materials with the surface soil. (3) Water immediately after application to maintain the soil moisture content at 60%-70% of the field water holding capacity. Maintain at room temperature for 30 days, avoiding rain erosion during this period.

[0041] The soil pH at the initial stage and after 3 months of treatment was measured using the glass electrode potentiometric method according to the "Determination of soil pH value by potentiometric method".

[0042] With reference to the “Microwave Digestion Method for the Determination of Metal Element Content in Soil and Sediment”, the As, Pb, and Cd contents in the soil were determined initially and after 3 months of treatment using inductively coupled plasma mass spectrometry.

[0043] The soil organic matter content at the initial stage and after 3 months of treatment was determined with reference to the potassium dichromate oxidation-external heating method in NY / T 1121.6-2006.

[0044] The number of soil microorganisms was determined initially and three months after treatment using the fumigation extraction method in GB / T 39228-2020.

[0045] The catalase (CAT) activity in the soil at the initial stage and after 3 months of treatment was determined by ultraviolet spectrophotometry, and the CAT enzyme activity was expressed as the change in absorbance at 240 nm. The superoxide dismutase (POD) activity in the soil at the initial stage and after 3 months of treatment was determined by guaiacol colorimetry, and the POD enzyme activity was calculated as the change in absorbance at 470 nm.

[0046] The As, Pb, and Cd contents in crops were determined with reference to GB 5009.268-2016. The sown crop was wheat (Yangmai 20 variety), with a sowing rate of 150 kg / ha, a row spacing of 20 cm, a sowing depth of 3-5 cm, and conventional field management. The growing period was 120 days. After wheat matured, the aboveground parts were collected, rinsed three times with deionized water, air-dried, and oven-dried at 80°C to constant weight. After microwave digestion, the As, Pb, and Cd contents in the digestion solution were determined by inductively coupled plasma-mass spectrometry.

[0047] Table 1 Test results of the passivation and remediation performance of heavy metal contaminated soil by the conditioners prepared in Examples 1-3 and Comparative Examples 1-3

[0048] From the test results in Table 1 above, it can be seen that the pH value of the soil was significantly improved after treatment in Examples 1-3. After 3 months, the As, Pb, and Cd contents of each example were reduced to 13.2-15.7 mg / kg, 54.7-60.3 mg / kg, and 0.9-1.2 mg / kg, respectively, with a removal rate of 63.2%-82.8%. The removal rate of the control example was only 32.8%-53.4%, and the removal capacity of heavy metals was significantly lower than that of the example. In addition, the soil organic matter content of each example increased by 50.4%-57.0%, the number of microorganisms increased by 290.6%-375.0%, and the CAT and POD activities increased by 171%-263% compared with the initial values, which were significantly better than the control example. When wheat was planted in the soil after passivation treatment, the As content, Pb content, and Cd content in the crops obtained in each example group were also significantly lower than those in the control example. This proves that the conditioner disclosed in the present invention has a significant effect on the passivation remediation of heavy metal contaminated soil.

[0049] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

[0050] The present invention and its embodiments are described above. Such description is not restrictive. The drawings show only one embodiment of the present invention, and actual applications are not limited thereto. In short, if a person skilled in the art is inspired by the above, and does not deviate from the purpose of the present invention, any method and embodiment similar to the technical solution without creative design shall fall within the scope of protection of the present invention.

Claims

1. A heavy metal contaminated soil passivation and remediation conditioner, characterized by: Prepared by the following steps: S1. Grind grapefruit peel into a particle size of 1-3 mm, heat to 500-520° C. at 10° C. / min under a nitrogen atmosphere and carbonize for 3 h, then immerse in a 20% mass concentration phosphoric acid solution, activate in a constant temperature water bath at 80° C. for 4 h, wash until neutral, and then dry in an oven at 105° C. for 12-18 h to obtain grapefruit peel activated carbon; S2, immersing the grapefruit peel activated carbon obtained in step S1 in a first mixed solution consisting of 0.2 mol / L ammonium molybdate and 0.1 mol / L sodium dihydrogen phosphate, adjusting the pH to 4.5, and reacting at 80° C. with stirring for 8 h. After the reaction is completed, centrifuging at 3000 rpm for 10 min, washing with deionized water three times, and vacuum drying at 80° C. for 6 h to obtain activated grapefruit peel activated carbon with ammonium phosphomolybdate loaded on its surface; S3, using stannous isooctanoate as a catalyst, ring-opening polymerizing caprolactone monomer at 120° C. for 24 hours under nitrogen protection to generate hydroxyl-terminated polycaprolactone, reacting the hydroxyl-terminated polycaprolactone with sodium azide in DMF at 60° C. for 24 hours to generate double-end azide-terminated polycaprolactone, and reacting the activated grapefruit peel activated carbon obtained in step S2 with a silane coupling agent in toluene at 60° C. for 12-18 hours, centrifuging and separating, and drying at 60-80° C. for 12-24 hours to obtain cross-linked modified activated carbon; S4, adding the cross-linked modified activated carbon obtained in step S3 and NO2A-butyne-di-tert-butyl ester to a 30% by mass DMF solution, and then adding the mixture to a second mixed solution consisting of 0.1 mol / L copper sulfate and 0.2 mol / L ascorbic acid, stirring at 40°C for 16 hours, filtering, washing, and drying to obtain a functionalized activated carbon composite material; S5. Add the product obtained in step S4 to a dichloromethane solution containing 5% trifluoroacetic acid, react at room temperature for 3 h to remove the tert-butyl ester protecting group, wash to neutrality after centrifugation, and dry to obtain a deprotected product. Disperse the deprotected product and 2-methacryloyloxyethyl phosphorylcholine in a phosphate buffer solution at pH 6.8, and ultrasonically treat at a power of 200 W and a frequency of 40 kHz for 30-60 min. Then, freeze-dry at -50°C for 48 h to obtain a finished conditioner.

2. The heavy metal contaminated soil passivation and remediation conditioner according to claim 1, characterized in that: In step S1, the feeding ratio of pomelo peel to phosphoric acid solution is 1 g: 3-6 mL.

3. The heavy metal contaminated soil passivation and remediation conditioner according to claim 1, characterized in that: In step S2, the feeding ratio of the grapefruit peel activated carbon to the first mixed solution is 1 g: 8-12 mL.

4. The heavy metal contaminated soil passivation and remediation conditioner according to claim 1, characterized in that: In step S3, the molar ratio of stannous isooctanoate to caprolactone monomer is 1:80-120.

5. The heavy metal contaminated soil passivation and remediation conditioner according to claim 1, characterized in that: The molecular weight of the hydroxyl-terminated polycaprolactone in step S3 is in the range of 5000-20000 Da, and the feeding ratio of the hydroxyl-terminated polycaprolactone, sodium azide and DMF is 1 g: 0.004-0.02 g: 20-40 mL.

6. The heavy metal contaminated soil passivation and remediation conditioner according to claim 1, characterized in that: In step S3, the feed ratio of activated grapefruit peel activated carbon, silane coupling agent and toluene is 1 g: 0.1-0.3 g: 10-20 mL, and the silane coupling agent is one or more of KH-550, KH-560 and KH-570.

7. The heavy metal contaminated soil passivation and remediation conditioner according to claim 1, characterized in that: In step S4, the feed ratio of the cross-linked modified activated carbon, NO2A-butyne-di-tert-butyl ester, DMF solution, and the second mixed solution is 1 g: 0.3-0.7 g: 15-25 mL: 20-40 mL.

8. The heavy metal contaminated soil passivation and remediation agent according to claim 1, characterized in that: In step S5, the charging ratio of the functionalized activated carbon composite material and the dichloromethane solution of trifluoroacetic acid is 1 g: 30-70 mL, and the charging ratio of the deprotected product, 2-methacryloyloxyethyl phosphorylcholine and phosphate buffer in step S5 is 1 g: 1-3 g: 20-40 mL.

9. Use of the heavy metal contaminated soil passivation and remediation conditioner according to any one of claims 1 to 8, characterized in that: By weight, 20-30 parts of conditioner are mixed evenly with 5-10 parts of potassium feldspar powder, 10-15 parts of calcium magnesium phosphate fertilizer, 15-25 parts of agricultural lime, 20-30 parts of humic acid, and 0.5-2 parts of microbial agent, and the heavy metal contaminated soil is passivated and repaired at an application rate of 3000 kg / hectare.

10. The use according to claim 9, characterized in that: The microbial agent includes Bacillus amyloliquefaciens, Bacillus subtilis, Aspergillus niger, Pseudomonas aeruginosa, and Streptomyces tenuifolius. The number of viable bacteria of Bacillus amyloliquefaciens is ≥1×10^8 CFU / g, the number of viable bacteria of Bacillus subtilis is ≥5×10^7 CFU / g, the number of viable bacteria of Aspergillus niger is ≥2×10^7 CFU / g, the number of viable bacteria of Pseudomonas aeruginosa is ≥2×10^7 CFU / g, and the number of viable bacteria of Streptomyces tenuifolius is ≥1×10^8 CFU / g.

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