Method for efficiently removing heavy metals in soil

Abstract

The invention discloses a method for efficiently removing heavy metals in soil, which comprises the steps of sample collection, sample pretreatment, supramolecular cage preparation, heavy metal capture, material screening and the like, heavy metals such as mercury, lead, cadmium and the like in the soil are captured through the supramolecular cage, and a magnetic carrier after capturing the heavy metals is removed through a magnetic separation mode; the process flow period is short, the heavy metal removal efficiency is high, no nanoparticle residue risk exists, the long-term leaching risk of apatite, bentonite and other curing agents in a traditional stabilization technology is avoided, environment friendliness is high, and the method is especially suitable for industrial sites, mining areas and other combined pollution scenes and has wide application prospects. And an innovative technical path capable of being popularized is provided for soil remediation.

Description

Technical Field

[0001] The present invention relates to the technical field of soil heavy metal treatment, and particularly relates to a method for efficiently removing heavy metals from soil. Background Art

[0002] The heavy metal problem in soil is a complex environmental issue, involving the dual impacts of natural processes and human activities; among them, natural process factors include bedrock weathering, volcanic eruptions, sedimentation cycles, etc., and human activity factors include industrial emissions, agricultural inputs, mining, electronic waste, etc.

[0003] Especially heavy metals represented by mercury, lead, and cadmium are difficult to be naturally degraded after entering the soil. Long-term accumulation will lead to a decline in soil fertility, affect the activity of soil microorganisms, have an impact on the ecological environment, plant growth, and soil animals, and will also pose a potential threat to human health through the enrichment effect of the food chain. Therefore, the digestion project of soil heavy metals is an issue that the agricultural field has to face.

[0004] Currently, the main methods for digesting soil heavy metals are as follows: physical measures (soil replacement, electrokinetic remediation), chemical passivation (biochar modification, phosphate degradation), bioremediation (hyperaccumulator plants, microbial enhancement), combined remediation (plant-mycorrhiza combination, chemical-biological combination). With the progress of technology, in recent years, some advanced technologies such as nanomaterial remediation and gene editing have emerged. However, these technologies all have some defects more or less. For example, the physical measures take too long and have low efficiency, the chemical passivation has a high risk of drug residues, and the nanoremediation also has a risk of nanoparticle residues.

[0005] Based on supramolecular cage technology, the present application has developed a method for efficiently removing heavy metals such as mercury, lead, and cadmium from soil. The so-called supramolecular cage is a molecular aggregate formed by two or more molecules through non-covalent interactions (such as hydrogen bonds, electrostatic interactions, hydrophobic interactions, van der Waals forces, etc.). The supramolecular cage has a unique cavity structure, which can enhance the affinity for specific molecules through dynamic changes and exhibit excellent recognition and encapsulation capabilities for specific guest molecules. Summary of the Invention

[0006] To achieve the above object, the present invention discloses a method for efficiently removing heavy metals from soil, including the following steps:

[0007] S1 - Sample collection: Take an appropriate amount of soil and pass it through a sieve to filter out large stones, soil clods, and sundries, and retain the soil sample that meets the size requirements;

[0008] S2 - Sample pretreatment: Put the collected soil sample into a test tray, add an appropriate amount of citric acid and tartaric acid to activate the heavy metal ions in the soil, and adjust the moisture content to 10 - 15%;

[0009] S3 - Preparation of supramolecular cages: Cucurbit[8]uril is used as the main framework, and thiol, phosphate, carboxylic acid / amino high - affinity groups are grafted on its cage wall and covalently connected with Fe3O4@SiO2 to form a supramolecular cage complex;

[0010] S4 - Heavy metal capture: Appropriate amount of the supramolecular cage complex is added to the test tray and left standing for 4 - 6 h to allow the supramolecular cage complex to react with the sample, thereby capturing Hg 2+ , Pb 2+ , Cd 2+ ions;

[0011] S5 - Material screening: The reacted material is placed in a vacuum drying oven for drying. After drying, a permanent magnet drum is used to recover the carrier after capturing heavy metal ions, and the remaining material is the soil after heavy metal removal.

[0012] Further, in step S1, the aperture of the sieve used for sieving is 5 - 8 mm.

[0013] Further, in step S2, the molar concentration of citric acid is 0.1 - 0.2 M, the pH value is 3.5 - 3.8, and the concentration of tartaric acid is 45 - 50%.

[0014] Further, in step S2, the addition ratio of citric acid to tartaric acid is 2:1.

[0015] Further, the specific steps for preparing the supramolecular cage in step S3 are as follows:

[0016] S31: Thiol modification of cucurbit[8]uril

[0017] Cucurbit[8]uril and 3 - mercaptopropyltrimethoxysilane are refluxed in DMF at a reaction temperature of 150 - 160 °C for 2 - 3 h, and 8 - SH groups are grafted onto each cucurbit[8]uril;

[0018] S32: Introduction of phosphate groups

[0019] The thiolated cucurbit[8]uril and trichloroethyl phosphate are coupled under the catalysis of EDC / NHS, and 4 - PO4 3- groups are introduced into each cucurbit[8]uril;

[0020] S33: Carboxylic acid / amino bifunctionalization

[0021] The remaining hydroxyl groups of the thiolated cucurbit[8]uril are subjected to an anhydride reaction with ethylenediaminetetraacetic acid to form an EDTA - cucurbit[8]uril complex;

[0022] S34: Magnetic composite assembly

[0023] Thiolated cucurbit[8]uril was covalently bonded to the surface of Fe3O4@SiO2 via an aminosilane to form a cucurbit[8]uril-SH / PO4 / EDTA@Fe3O4 complex.

[0024] Further, in step S4, the -SH group captures Hg 2+ by binding through an Hg-S bond, and the -PO4 3- group captures Pb by utilizing the strong coordination ability of Pb 2+ with -PO4 3- , and the -COOH group and -NH2 group capture Cd 2+ to form a stable Cd-O / N five-membered ring structure. 2+

[0025] Further, in step S5, the drying temperature of the vacuum drying oven is 60 - 65 °C, and the drying time is 0.5 - 1 h.

[0026] Further, in step S5, the rotation speed of the permanent magnet drum is set to 40 - 50 r / min, and the number of times of material screening is 2 - 3 times.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] The present invention captures heavy metals such as mercury, lead, and cadmium in soil through a supramolecular cage, and removes the magnetic carrier after capturing heavy metals by magnetic separation. The process flow cycle is short, the heavy metal removal efficiency is high, there is no risk of nanoparticle residue, and the long-term leaching risk of solidifying agents such as apatite and bentonite in traditional stabilization technologies is avoided. It has strong environmental friendliness and is especially suitable for composite pollution scenarios such as industrial sites and mining areas, providing a promotable innovative technical path for soil remediation. Specific Embodiments

[0029] The technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments.

[0030] Example 1:

[0031] The method for efficient removal of heavy metals in soil in this example includes the following steps:

[0032] S1 - Sample collection: Take an appropriate amount of soil and pass it through a sieve to filter out large stones, soil clods, weeds, plastic films and other sundries, and retain the soil sample that meets the size requirements; among them, the aperture of the sieve used for sieving is 5 mm.

[0033] S2 - Sample pretreatment: Put the collected soil samples into the test trays, add appropriate amounts of citric acid and tartaric acid to activate the heavy metal ions in the soil, and adjust the moisture content to 10%; among them, the test trays are round or square glass or ceramic containers, the molar concentration of citric acid used is 0.1M, the pH value is 3.8, the concentration of tartaric acid is 50%, and the addition ratio of citric acid to tartaric acid is 2:1.

[0034] Citric acid and tartaric acid are added by spraying, which can make them penetrate more fully and evenly into the soil. Select whether to sprinkle water according to the soil humidity, and measure the moisture content of the soil with a handheld soil moisture detector to ensure that the moisture content is 10%.

[0035] Heavy metals usually exist in the form of metal ions in the soil, and the acidic root ions in citric acid and tartaric acid will form complexes with metal cations, so that the dissolution rate of Hg 2+ , Pb 2+ , Cd 2+ in the soil can reach more than 95%, providing a basic guarantee for the subsequent removal of heavy metal ions.

[0036] S3 - Preparation of supramolecular cage: Using cucurbit[8]uril as the main framework, grafting thiol, phosphate ester, carboxylic acid / amino high-affinity groups on its cage wall, and covalently connecting with Fe3O4@SiO2 to form a supramolecular cage complex; the specific preparation steps of this supramolecular cage complex are as follows:

[0037] S31: Thiol modification of cucurbit[8]uril

[0038] Reflux cucurbit[8]uril and 3-mercaptopropyltrimethoxysilane in DMF at a reaction temperature of 150°C for 3 hours, and graft 8 -SH groups to each cucurbit[8]uril.

[0039] Cucurbit[8]uril is a supramolecular compound, and its chemical structure is a hollow gourd-shaped structure composed of eight nitrogen-oxygen heterocyclic groups (C3H3NO). Due to its unique cavity structure, it can form stable host-guest complexes with compatible molecules, so it can be used for molecular recognition and separation.

[0040] 3-Mercaptopropyltrimethoxysilane is a sulfur-containing silane compound, which contains an active organic mercapto group (-SH) and three hydrolyzable methoxy groups (CH3O-), and each nitrogen-oxygen heterocycle couples an organic mercapto group (-SH), thus forming cucurbit[8]uril with 8 -SH groups.

[0041] DMF is N,N-dimethylformamide, which has good solubility for a variety of organic and inorganic compounds and is used here as the reaction solvent for cucurbit[8]uril and 3-mercaptopropyltrimethoxysilane.

[0042] S32: Introduction of phosphate ester group

[0043] Couple thiolated cucurbit[8]uril with trichloroethyl phosphate under the catalysis of EDC / NHS, introducing 4 -PO4 groups into each cucurbit[8]uril; among them, EDC / NHS is a commonly used coupling method in the chemical field, which can separate the phosphate ion (-PO4) of trichloroethyl phosphate and couple it with thiolated cucurbit[8]uril. 3- 3-

[0044] S33: Carboxylic acid / amino bifunctionalization

[0045] Perform an anhydride reaction on the remaining hydroxyl groups (-OH) of thiolated cucurbit[8]uril with ethylenediaminetetraacetic acid to form an EDTA-cucurbit[8]uril complex. Specifically, esters and amides can be generated during the anhydride reaction, and ethylenediaminetetraacetic acid is connected to the hydroxyl group (-OH) of cucurbit[8]uril through an ester bond or an amide bond to form a stable covalent bond.

[0046] Since consuming 1 hydroxyl group (-OH) and removing 1 molecule of water (H2O) are required for each connection of 1 ethylenediaminetetraacetic acid molecule, there are two reaction paths for the generated EDTA-cucurbit[8]uril complex:

[0047] (1) If 1 ethylenediaminetetraacetic acid molecule is grafted onto each thiolated cucurbit[8]uril, the reaction equation is:

[0048] ‌C 48 H 48 N 32 O 16 + C 10 H 16 N2O8-H2O → C 58 H 62 N 34 O 23 ‌

[0049] (2) If 4 ethylenediaminetetraacetic acid molecules are grafted (for example, modified at 4 hydroxyl sites of cucurbit[8]uril), the reaction equation is:

[0050] ‌C 48 H 48 N 32 O 16 + 4(C 10 H 16 N2O8)-4H2O → C 88 H 100 N 40 O 44 ​​

[0051] S34: Magnetic composite assembly

[0052] Thiolated cucurbit[8]uril was covalently bonded to the surface of Fe3O4@SiO2 through aminosilane to form a cucurbit[8]uril-SH / PO4 / EDTA@Fe3O4 complex. TEM showed that the coating thickness of the above complex was 5 nm.

[0053] S4 - Heavy metal capture: An appropriate amount of supramolecular cage complex was added to the test tray and left standing for 4 h to allow the supramolecular cage complex to react with the sample, thereby capturing Hg 2+ , Pb 2+ , Cd 2+ ions in the soil sample.

[0054] Among them, the -SH group captures Hg 2+ by binding through the Hg-S bond, and the -PO4 3- group captures Pb 2+ using the strong coordination ability of Pb 3- with -PO4 2+ , and the -COOH group and -NH2 group capture Cd 2+ to form a stable Cd-O / N five-membered ring structure.

[0055] S5 - Material screening: The material after the reaction was placed in a vacuum drying oven for drying. After drying, a permanent magnet drum was used to recover the carrier after capturing heavy metal ions, and the remaining material was the soil after heavy metals were removed.

[0056] Among them, the drying temperature of the vacuum drying oven was 60 °C, and the drying time was 0.5 h; the rotation speed of the permanent magnet drum was set at 40 r / min, and the number of material screening times was 3 times.

[0057] Example 2:

[0058] The method for efficient removal of heavy metals from soil in this example includes the following steps:

[0059] S1 - Sample collection: An appropriate amount of soil was taken and sieved to filter out large stones, soil clods, weeds, plastic films and other sundries, and the soil sample meeting the size requirements was retained; among them, the aperture of the sieve used for sieving was 6 mm.

[0060] S2 - Sample pretreatment: The collected soil sample was placed in a test tray, and an appropriate amount of citric acid and tartaric acid were added to activate the heavy metal ions in the soil and adjust the moisture content to 12%; among them, the test tray was a round or square glass or ceramic vessel, the molar concentration of citric acid used was 0.15 M, the pH value was 3.6, the concentration of tartaric acid was 48%, and the addition ratio of citric acid to tartaric acid was 2:1.

[0061] Citric acid and tartaric acid are added by spraying, so that they can penetrate more fully and evenly into the soil. Whether to sprinkle water is selected according to the soil humidity, and the water content of the soil is measured by a handheld soil moisture detector to ensure that the water content is 12%.

[0062] Heavy metals usually exist in the form of metal ions in the soil, and the acidic root ions in citric acid and tartaric acid will form complexes with metal cations, so that the dissolution rate of Hg 2+ , Pb 2+ , Cd 2+ in the soil can reach more than 95%, providing a basic guarantee for the subsequent removal of heavy metal ions.

[0063] S3 - Preparation of supramolecular cage: Cucurbit[8]uril is used as the main framework, and thiol, phosphate ester, carboxylic acid / amino high - affinity groups are grafted on its cage wall and covalently connected with Fe3O4@SiO2 to form a supramolecular cage complex; The specific preparation steps of this supramolecular cage complex are as follows:

[0064] S31: Thiol modification of cucurbit[8]uril

[0065] Cucurbit[8]uril is refluxed with 3 - mercaptopropyltrimethoxysilane in DMF at a reaction temperature of 155 °C for 2.5 h, and 8 - SH groups are grafted onto each cucurbit[8]uril.

[0066] Cucurbit[8]uril is a supramolecular compound, and its chemical structure is a hollow gourd - like structure composed of eight nitrogen - oxygen heterocyclic groups (C3H3NO). Due to its unique cavity structure, it can form stable host - guest complexes with compatible molecules, so it can be used for molecular recognition and separation.

[0067] 3 - Mercaptopropyltrimethoxysilane is a sulfur - containing silane compound, which contains an active organic mercapto group (-SH) and three hydrolyzable methoxy groups (CH3O-), and each nitrogen - oxygen heterocycle is coupled with an organic mercapto group (-SH) to form cucurbit[8]uril with 8 - SH groups.

[0068] DMF is N,N - dimethylformamide, which has good solubility for a variety of organic and inorganic compounds and is used as the reaction solvent for cucurbit[8]uril and 3 - mercaptopropyltrimethoxysilane here.

[0069] S32: Introduction of phosphate ester groups

[0070] The thiolated cucurbit[8]uril is coupled with trichloroethyl phosphate under the catalysis of EDC / NHS, and 4 - PO4 are introduced into each cucurbit[8]uril 3-Group; among them, EDC / NHS is a commonly used coupling method in the chemical field, which can separate the phosphate ion (-PO4 3- ) of trichloroethyl phosphate and couple it with thiolated cucurbit[8]uril.

[0071] S33: Carboxylic acid / amino bifunctionalization

[0072] The remaining hydroxyl groups (-OH) of thiolated cucurbit[8]uril are subjected to an acid anhydride reaction with ethylenediaminetetraacetic acid to form an EDTA-cucurbit[8]uril complex. Specifically, esters and amides can be generated during the acid anhydride reaction, and ethylenediaminetetraacetic acid is connected to the hydroxyl group (-OH) of cucurbit[8]uril through an ester bond or an amide bond to form a stable covalent bond.

[0073] Since each time 1 molecule of ethylenediaminetetraacetic acid is connected, 1 hydroxyl group (-OH) needs to be consumed and 1 molecule of water (H2O) is removed, there are two reaction paths for the generated EDTA-cucurbit[8]uril complex:

[0074] (1) If each thiolated cucurbit[8]uril grafts 1 molecule of ethylenediaminetetraacetic acid, the reaction equation is:

[0075] ‌C 48 H 48 N 32 O 16 + C 10 H 16 N2O8-H2O → C 58 H 62 N 34 O 23 ‌

[0076] (2) If 4 molecules of ethylenediaminetetraacetic acid are grafted (for example, modified at 4 hydroxyl sites of cucurbit[8]uril), the reaction equation is:

[0077] ‌C 48 H 48 N 32 O 16 + 4(C 10 H 16 N2O8)-4H2O → C 88 H 100 N 40 O 44

[0078] S34: Magnetic composite assembly

[0079] Thiolated cucurbit[8]uril was covalently bonded to the surface of Fe3O4@SiO2 through aminosilane to form a cucurbit[8]uril-SH / PO4 / EDTA@Fe3O4 complex. As shown by TEM, the coating layer of the above complex had a thickness of 6 nm.

[0080] S4 - Heavy metal capture: An appropriate amount of supramolecular cage complex was added to the test tray and left standing for 5 h to allow the supramolecular cage complex to react with the sample, thereby capturing Hg 2+ , Pb 2+ , Cd 2+ ions in the soil sample.

[0081] Among them, the -SH group captures Hg 2+ by binding through the Hg-S bond, and the -PO4 3- group captures Pb 2+ using the strong coordination ability of Pb 3- with -PO4 2+ , and the -COOH group and -NH2 group capture Cd 2+ to form a stable Cd-O / N five-membered ring structure.

[0082] S5 - Material screening: The material after the reaction was placed in a vacuum drying oven for drying. After drying, a permanent magnet drum was used to recover the carrier that had captured heavy metal ions, and the remaining material was the soil with heavy metals removed.

[0083] Among them, the drying temperature of the vacuum drying oven was 62 °C, and the drying time was 0.8 h; the rotation speed of the permanent magnet drum was set at 42 r / min, and the number of material screening times was 3 times.

[0084] Example 3:

[0085] The method for efficiently removing heavy metals from the soil in this example includes the following steps:

[0086] S1 - Sample collection: An appropriate amount of soil was taken and sieved to filter out large stones, soil clods, weeds, plastic films and other sundries, and the soil sample that met the size requirements was retained; among them, the aperture of the sieve used for sieving was 8 mm.

[0087] S2 - Sample pretreatment: The collected soil sample was placed in a test tray, and an appropriate amount of citric acid and tartaric acid were added to activate the heavy metal ions in the soil and adjust the moisture content to 15%; among them, the test tray was a round or square glass or ceramic vessel, the molar concentration of citric acid used was 0.2 M, the pH value was 3.5, the concentration of tartaric acid was 45%, and the addition ratio of citric acid to tartaric acid was 2:1.

[0088] Citric acid and tartaric acid are added by spraying, which can make them penetrate more fully and evenly into the soil. Whether to sprinkle water is selected according to the soil humidity, and the moisture content of the soil is measured by a handheld soil moisture detector to ensure that the moisture content is 15%.

[0089] Heavy metals usually exist in the form of metal ions in the soil, and the acidic root ions in citric acid and tartaric acid will form complexes with metal cations, so that the dissolution rate of Hg 2+ 、Pb 2+ 、Cd 2+ in the soil can reach more than 95%, providing a basic guarantee for the subsequent removal of heavy metal ions.

[0090] S3 - Preparation of supramolecular cage: Cucurbit[8]uril is used as the main framework, and thiol, phosphate ester, carboxylic acid / amino high - affinity groups are grafted on its cage wall and covalently connected with Fe3O4@SiO2 to form a supramolecular cage complex; the specific preparation steps of this supramolecular cage complex are as follows:

[0091] S31: Thiol modification of cucurbit[8]uril

[0092] Cucurbit[8]uril is refluxed with 3 - mercaptopropyltrimethoxysilane in DMF at a reaction temperature of 160 °C for 2 h, and 8 - SH groups are grafted onto each cucurbit[8]uril.

[0093] Cucurbit[8]uril is a supramolecular compound, and its chemical structure is a hollow gourd - like structure composed of eight nitrogen - oxygen heterocyclic groups (C3H3NO). Due to its unique cavity structure, it can form stable host - guest complexes with compatible molecules, so it can be used for molecular recognition and separation.

[0094] 3 - Mercaptopropyltrimethoxysilane is a sulfur - containing silane compound, which contains an active organic mercapto group (-SH) and three hydrolyzable methoxy groups (CH3O-), and each nitrogen - oxygen heterocycle is coupled with an organic mercapto group (-SH) to form cucurbit[8]uril with 8 - SH groups.

[0095] DMF is N,N - dimethylformamide, which has good solubility for a variety of organic and inorganic compounds and is used as the reaction solvent for cucurbit[8]uril and 3 - mercaptopropyltrimethoxysilane here.

[0096] S32: Introduction of phosphate ester groups

[0097] Thiolated cucurbit[8]uril is coupled with trichloroethyl phosphate under the catalysis of EDC / NHS, and 4 - PO4 are introduced into each cucurbit[8]uril 3-Group; among them, EDC / NHS is a commonly used coupling method in the chemical field, which can separate the phosphate ion (-PO4 3- ) of trichloroethyl phosphate and couple it with thiolated cucurbit[8]uril.

[0098] S33: Carboxylic acid / amino bifunctionalization

[0099] The remaining hydroxyl groups (-OH) of thiolated cucurbit[8]uril are subjected to an anhydride reaction with ethylenediaminetetraacetic acid to form an EDTA-cucurbit[8]uril complex. Specifically, esters and amides can be generated during the anhydride reaction, and ethylenediaminetetraacetic acid is connected to the hydroxyl group (-OH) of cucurbit[8]uril through an ester bond or an amide bond to form a stable covalent bond.

[0100] Since each connection of 1 ethylenediaminetetraacetic acid molecule consumes 1 hydroxyl group (-OH) and removes 1 molecule of water (H2O), there are two reaction paths for the generated EDTA-cucurbit[8]uril complex:

[0101] (1) If each thiolated cucurbit[8]uril grafts 1 ethylenediaminetetraacetic acid molecule, the reaction equation is:

[0102] ‌C 48 H 48 N 32 O 16 + C 10 H 16 N2O8-H2O → C 58 H 62 N 34 O 23 ‌

[0103] (2) If 4 ethylenediaminetetraacetic acid molecules are grafted (for example, modified at 4 hydroxyl sites of cucurbit[8]uril), the reaction equation is:

[0104] ‌C 48 H 48 N 32 O 16 + 4(C 10 H 16 N2O8)-4H2O → C 88 H 100 N 40 O 44

[0105] S34: Magnetic composite assembly

[0106] The mercapto cucurbit[8]uril was covalently bonded to the surface of Fe3O4@SiO2 through aminosilane to form a cucurbit[8]uril-SH / PO4 / EDTA@Fe3O4 complex. As shown by TEM, the coating layer thickness of the above complex was 6 nm.

[0107] S4 - Heavy metal capture: An appropriate amount of supramolecular cage complex was added to the test tray and allowed to stand for 4 h to react the supramolecular cage complex with the sample, thereby capturing Hg 2+ , Pb 2+ , Cd 2+ ions in the soil sample.

[0108] Among them, the -SH group captures Hg 2+ by binding through the Hg-S bond, and the -PO4 3- group captures Pb 2+ using the strong coordination ability of Pb 3- with -PO4 2+ , and the -COOH group and -NH2 group capture Cd 2+ to form a stable Cd-O / N five-membered ring structure.

[0109] S5 - Material screening: The materials after the reaction were placed in a vacuum drying oven for drying. After drying, a permanent magnet drum was used to recover the carrier after capturing heavy metal ions, and the remaining materials were the soil after removing heavy metals.

[0110] Among them, the drying temperature of the vacuum drying oven was 65°C, and the drying time was 1 h; the rotation speed of the permanent magnet drum was set to 45 r / min, and the material screening was carried out 2 times.

[0111] The above examples were carried out in a laboratory environment with constant temperature (25°C) and constant humidity (40%) for a control test. The specific test results are shown in the following table:

[0112] Group Supramolecular cage addition amount Reaction time <![CDATA[Hg 2+ Removal rate]]> <![CDATA[Pb 2+ Removal rate]]> <![CDATA[Cd 2+ Removal rate]]> Example 1 10 mg / g soil 6h 98.3% 98.5% 98.8% Example 2 12 mg / g soil 6h 96.7% 96.9% 97.0% Example 3 15 mg / g soil 6h 95.5% 95.7% 96.1%

[0113] From the above control test, it can be seen that after adopting this method, the removal rate of heavy metal ions in the soil is more than 95%. Among them, the removal rate of Hg 2+ is more than 98.3%, the removal rate of Pb 2+ is more than 96.7%, and the removal rate of Cd 2+ is more than 95.5%. Moreover, the process flow cycle is short, the heavy metal removal efficiency is high, there is no risk of nanoparticle residue, and the long-term leaching risk of solidifying agents such as apatite and bentonite in traditional stabilization technologies is avoided. It has strong environmental friendliness and is especially suitable for composite pollution scenarios such as industrial sites and mining areas, providing a popularizable innovative technical path for soil remediation.

[0114] In addition, the screened magnetic carriers can desorb Hg 2+ , Pb 2+ , Cd 2+ for recycling, thus realizing the resource recovery and utilization of heavy metals, which is conducive to cost reduction.

[0115] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention. In addition, the technical solutions between various embodiments can be combined with each other, but it must be based on the fact that those skilled in the art can implement them; when the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the protection scope required by the present invention.

Claims

1. A method for efficiently removing heavy metals from soil, characterized in that: The following steps are involved: S1-Sample collection: Take an appropriate amount of soil and sieve it, filter out large stones, soil blocks and debris, and retain soil samples that meet the size requirements; S2-Sample pretreatment: Place the collected soil samples in a test tray, add appropriate amounts of citric acid and tartaric acid to activate the heavy metal ions in the soil, and adjust the moisture content to 10-15%; S3-Preparation of supramolecular cage: Using cucurbitacin[8]uril as the main framework, grafting thiol, phosphate, carboxylic acid / amino high affinity groups on its cage wall, and covalently linking it with Fe3O4@SiO2 to form a supramolecular cage complex; S4-Heavy metal capture: Add an appropriate amount of supramolecular cage complex to the test tray and let it stand for 4-6 hours to allow the supramolecular cage complex to react with the sample, thereby capturing Hg2+, Pb2+, and Cd2+ ions in the soil sample; S5-Material screening: The materials after the reaction are placed in a vacuum drying oven for drying. After drying, the carriers that have captured heavy metal ions are recovered using a permanent magnetic drum. The remaining material is the soil after the heavy metals have been removed.

2. The method for efficiently removing heavy metals in soil according to claim 1, characterized in that: In step S1, the mesh size used for screening is 5-8 mm.

3. The method for efficiently removing heavy metals in soil according to claim 1, characterized in that: In step S2, the molar concentration of citric acid is 0.1-0.2 M, the pH value is 3.5-3.8, and the concentration of tartaric acid is 45-50%.

4. The method for efficiently removing heavy metals from soil according to claim 1, characterized in that: In step S2, the addition ratio of citric acid to tartaric acid is 2:

1.

5. The method for efficiently removing heavy metals from soil according to claim 1, characterized in that: The specific steps of preparing the supramolecular cage in step S3 are as follows: S31: Cucurbit[8]urea Thiol Modification ‌Cucurbitacin[8]uril and 3-mercaptopropyltrimethoxysilane were refluxed in DMF at a reaction temperature of 150-160°C for 2-3 hours, and each cucurbitacin[8]uril was grafted with 8 -SH groups; S32: Introduction of phosphate groups The thiolated cucurbit[8]uril was coupled with trichloroethyl phosphate under EDC / NHS catalysis to introduce four -PO43- groups into each cucurbit[8]uril; S33: Carboxylic acid / amino difunctionalization The remaining hydroxyl groups of the thiolated cucurbitac[8]uril are reacted with ethylenediaminetetraacetic acid anhydride to form an EDTA-cucurbitac[8]uril complex; S34: Magnetic Composite Assembly‌ Thiolated cucurbitac[8]uril was covalently bonded to the Fe3O4@SiO2 surface via aminosilane to form a cucurbitac[8]uril-SH / PO4 / EDTA@Fe3O4 complex.

6. The method for efficiently removing heavy metals from soil according to claim 1, characterized in that: In step S4, the -SH group captures Hg2+ through the Hg-S bond, the -PO43- group captures Pb2+ by utilizing the strong coordination ability of Pb2+ and -PO43-, and the -COOH group and -NH2 group capture Cd2+ to form a stable Cd-O / N five-membered ring structure.

7. The method for efficiently removing heavy metals in soil according to claim 1, characterized in that: In step S5, the drying temperature of the vacuum drying oven is 60-65°C, and the drying time is 0.5-1h.

8. The method for efficiently removing heavy metals in soil according to claim 1, characterized in that: In step S5, the rotation speed of the permanent magnet drum is set to 40-50 r / min, and the material screening times is 2-3 times.