Method for enhancing phytoremediation of cadmium-contaminated soil by using degradable chelating agent

Abstract

The invention provides a method for enhancing phytoremediation of cadmium-contaminated soil by using a degradable chelating agent, which comprises the following steps: selecting torch cockscomb seedlings with relatively strong enrichment capacity on cadmium metal, planting the seedlings into a cadmium-contaminated soil layer to be remedied, and spraying a special green degradable composite chelating agent for several times in a growth cycle, so that the cadmium-contaminated soil layer to be remedied is obtained. Therefore, activation and release of cadmium in the soil layer to be repaired are promoted, the extraction efficiency of the torch cockscombs on cadmium is enhanced, and meanwhile growth of the torch cockscombs is promoted. Compared with a chelating agent with a single component, the composite chelating agent with preferable components and content is sprayed into the cadmium-polluted soil, and the purification efficiency of the torch cockscomb on cadmium can be more effectively improved. Moreover, according to the method, the gravel layer, the coarse gravel mixing layer and the adsorption material layer are built below the cadmium-polluted soil layer to be repaired, so that cadmium pollutants are prevented from being migrated into underground water, and secondary pollution is avoided. The method is low in remediation cost, environmentally friendly and especially suitable for remediation of moderately and severely cadmium contaminated soil.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of environmental pollution ecological restoration and remediation, and particularly relates to a method for strengthening plant remediation of cadmium contaminated soil by using degradable chelating agents. BACKGROUND

[0002] Heavy metal elements in the field of environmental pollution generally refer to heavy elements with significant toxicity to animals and plants, such as cadmium (Cd), mercury (Hg), lead (Pb), copper (Cu), chromium (Cr), nickel (Ni), zinc (Zn), antimony (Sb), cobalt (Co) and metalloid arsenic (As) and the like. The accumulation of heavy metals significantly exceeds the background value of the element in the soil, and causes the phenomenon of soil quality decline and ecological environment deterioration, i.e. soil heavy metal pollution.

[0003] With the gradual acceleration of industrialization, urbanization and rural modernization process, the discharge of industrial "three wastes", motor vehicle exhaust, sewage irrigation and the use of pesticides, herbicides, fertilizers and the development of mining industry, leading to serious over-standard of heavy metals in soil. The "National Soil Pollution Status Investigation Bulletin" released in 2014 investigated all the cultivated land, part of the forest land, grassland, unused land and construction land in China. The total over-standard rate of soil in China was 16.1%, of which more than 4 / 5 was caused by inorganic pollutants such as heavy metals. The leaching of heavy metals in the soil profile is a very slow process, so the heavy metal content in the surface layer of soil is easy to reach the toxicity level. Heavy metals in soil have the characteristics of persistence, hidden plant absorption and non-degradability, which can be easily absorbed by plants and transferred to different parts, and through the biological amplification of food chain, it brings direct harm to food safety and human health. Therefore, the remediation of heavy metals in soil has important significance for improving the ecological environment, ensuring food safety, protecting public health and the like.

[0004] For heavy metal contaminated soil, the technology level considers "deactivation, total amount, and risk reduction", that is, through a series of technologies to remove heavy metals in soil or reduce the effectiveness and activity of heavy metals, so as to reduce the migration of heavy metals in soil to food chain and groundwater, and restore the normal function of soil ecosystem. Heavy metal contaminated soil remediation technology can be divided into four categories according to the classification of disciplines: physical method, chemical method, biological method and agricultural ecological method. Among them, physical method mainly includes guest soil, surface soil removal, deep ploughing, etc., which is adopted in developed countries such as the United States, Japan and the Netherlands, but the treatment cost is high and it is suitable for small area of soil pollution; Electric remediation is still limited to laboratory research stage, and there are few reports on actual pollution site remediation; Chemical method includes solidification, stabilization and soil leaching. Solidification / stabilization remediation is a risk control method, which does not completely remove heavy metals in soil, but leads to long-term accumulation of heavy metals, which needs long-term management and monitoring of soil; Soil leaching is a process of washing or desorbing pollutants by applying water, surfactants or solutions containing chelating agents, which can be divided into in-situ remediation and ex-situ remediation. Leaching technology can completely eliminate the risk of heavy metal pollution, and in-situ leaching can treat contaminated soil on site, with fast effect, outstanding remediation effect and little damage to soil ecosystem, but it is difficult to collect leaching waste liquid and easy to pollute groundwater.

[0005] Biological method includes animal remediation, plant remediation and microbial remediation, animal remediation and microbial remediation is a method of using animal or microbial activity to change the activity of heavy metals, which has limited effect on heavy metal removal. Plant remediation process includes plant extraction, plant volatilization, plant fixation, plant transformation and plant degradation. In the past two decades, plant remediation of heavy metal contaminated soil has been increasingly concerned because of its environmental friendliness and low cost compared with other traditional methods. The so-called plant extraction refers to the use of hyperaccumulator extraction to remove heavy metals in contaminated soil. The main problem hindering the efficiency of plant remediation is that the bioavailability of metals in contaminated soil is relatively low. In addition, under natural conditions, their plant extraction rate is usually limited by the solubility and diffusion of metals on the root surface. At the same time, due to the existence of heavy metals in contaminated soil, the main form is difficult to absorb, and the process of transforming difficult to absorb heavy metals into plant absorbable state through exchange state is very slow, which needs several repeated planting of hyperaccumulator to reduce the content of heavy metals in contaminated soil to an acceptable level, and the whole remediation takes too long time.

[0006] The strengthening techniques of phytoremediation include chemical strengthening, microbial strengthening, animal strengthening, carbon dioxide strengthening, agronomic and management measures strengthening, etc. The chemical strengthening mainly embodies two aspects: one is to change the form of heavy metals by using chemical substances, so that the heavy metals are converted from the combined state to the water-soluble exchange state, thereby improving the bioavailability and the efficiency of phytoremediation; the other is to improve the biomass of plants (especially the aboveground part), thereby increasing the total amount of heavy metals absorbed by plants. Some synthetic chelates, such as ethylenediaminetetraacetic acid (EDTA), trans-1,2-diaminocyclohexane-N,N,N',N'-tetraacetic acid (EGTA), nitrilotriacetic acid (NTA), ethylene glycol-bis(β-aminoethylether) and ethylenediamine-di(o-hydroxyphenylacetic acid) (EDDHA), have been used to enhance the absorption of heavy metals by plants. Chelating agents can promote the conversion of heavy metals to water-soluble exchange state, thereby improving the efficiency of phytoremediation. However, in 2017, the WHO listed NTA as a carcinogen, and chelating agents such as EDTA have strong biochemical stability in the environment, and the residual time of high-concentration metal-chelating agent complexes is long, which poses a potential threat to groundwater pollution, so it is necessary to study chelating agents with biodegradability and environmental friendliness. SUMMARY

[0007] In view of the above problems existing in the prior art, the present application provides a method for strengthening phytoremediation of cadmium-contaminated soil by using degradable chelating agents, aiming to solve the problems of low remediation efficiency and easy pollution of cadmium-containing waste liquid to groundwater in the existing method for phytoremediation of contaminated soil. The method selects torch poinsettia as a hyperaccumulator, and prepares a specific composite chelating agent to promote the activation and release of cadmium in moderately to severely cadmium-contaminated soil, thereby strengthening the extraction efficiency of cadmium by torch poinsettia. The specific application content is as follows:

[0008] In the first aspect, the present application provides a method for strengthening phytoremediation of cadmium-contaminated soil by using degradable chelating agents, which comprises the following steps:

[0009] S1, a box without cover is prepared, a detachable partition is arranged at a distance of 100-300 mm from the bottom of the box, and a space above the detachable partition is sequentially laid with a gravel layer, a coarse sand and gravel mixed layer, an adsorption material layer and a cadmium-contaminated soil layer to be remediated with a cadmium concentration of 2-10 mg / kg from bottom to top;

[0010] S2, the torch poinsettia seedlings after cultivation are transplanted into the cadmium-contaminated soil layer to be remediated, and the composite chelating agent is sprayed at the 1st day, the 15th day and the 30th day respectively to strengthen the extraction efficiency of cadmium in the cadmium-contaminated soil layer to be remediated by plants; the leachate is collected, and the concentration of cadmium is determined;

[0011] S3, collecting the mature torch rooster comb plants, shaking off the soil adhered to the roots as the rhizosphere soil, determining the cadmium concentration of the rhizosphere soil; washing the torch rooster comb plants thoroughly, killing green at 100-110 DEG C for 30-90 min, then drying at 70 DEG C until constant weight, crushing, using nitric acid digestion, using a mass spectrometer to determine the cadmium concentration in the digestion solution;

[0012] The thickness of the gravel layer is 20-200 mm, the thickness of the coarse sand and gravel mixed layer is 20-200 mm, the thickness of the adsorption material layer is 20-200 mm, and the thickness of the cadmium contaminated soil layer is 50-500 mm.

[0013] The composite chelating agent is prepared by mixing 0.1-0.5 mol / L polyglutamic acid (γ-PGA) and 0.05-0.2 mol / L hexanediamine tetramethylene phosphonic acid (HDTMPA) in a volume ratio of 1-4:1.

[0014] Alternatively, the composite chelating agent is prepared by mixing 0.5 mol / L polyglutamic acid (γ-PGA) and 0.2 mol / L hexanediamine tetramethylene phosphonic acid (HDTMPA) in a volume ratio of 1:1.

[0015] Alternatively, the single spraying amount of the composite chelating agent is 3-5 L / m 2 .

[0016] Alternatively, the thickness of the gravel layer is 100 mm, the thickness of the coarse sand and gravel mixed layer is 100 mm, and the thickness of the adsorption material layer is 100 mm.

[0017] Alternatively, the thickness of the cadmium contaminated soil layer to be repaired is 300-500 mm.

[0018] Alternatively, the cadmium concentration of the cadmium contaminated soil layer to be repaired is 10 mg / kg.

[0019] Alternatively, the cultivated torch rooster seedlings are obtained by the following method:

[0020] The soil of the same source as the cadmium contaminated soil layer to be repaired is laid in a constant temperature incubator at 20 DEG C, and then the torch rooster is seeded or cut in the soil to obtain the cultivated torch rooster seedlings; the height of the cultivated torch rooster seedlings is 10-15 cm.

[0021] Alternatively, the detachable partition is provided with holes, the hole diameter of the holes is 10 mm, and the spacing between adjacent holes is 50 mm.

[0022] Alternatively, the cadmium concentration of the rhizosphere soil is determined by the following method:

[0023] The rhizosphere soil is dried at 70 DEG C, crushed through a 100 mesh screen, digested with a mixture of perchloric acid, hydrofluoric acid and nitric acid, and then the cadmium concentration of the digestion solution is determined by mass spectrometry.

[0024] Optionally, the temperature of the fixation is 105 DEG C and the time is 30 minutes.

[0025] Compared with the prior art, the application has the following advantages:

[0026] The application provides a method for strengthening plant remediation of cadmium contaminated soil by using degradable chelating agents, selects torch poinsettia seedlings with strong enrichment capacity for cadmium metal, plants the torch poinsettia seedlings in a cadmium contaminated soil layer to be remediated, and sprays special green degradable composite chelating agents in batches in a growth cycle to promote activation and release of cadmium in the cadmium contaminated soil layer to be remediated, so that the extraction efficiency of the torch poinsettia for cadmium is strengthened, and the growth of the torch poinsettia is promoted. Test results show that, compared with a single component chelating agent, spraying of the composite chelating agent with optimal components and contents in the cadmium contaminated soil can more effectively improve the purification efficiency of the torch poinsettia for cadmium. The enrichment coefficient and the transfer coefficient of the torch poinsettia for cadmium can be increased to 1.35 and 1.43 respectively, and the cadmium purification efficiency is greatly improved. Moreover, the method prevents migration of cadmium pollutants to underground water by building a gravel layer, a coarse sand and gravel mixed layer and an adsorption material layer below the contaminated soil layer to be remediated, so that secondary pollution is avoided. The method has low remediation cost and is environment-friendly, and is particularly suitable for remediation of medium and heavy cadmium contaminated soil. BRIEF DESCRIPTION OF DRAWINGS

[0027] In order to more clearly illustrate the technical solutions of the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description only show some embodiments of the present application, and other drawings can be obtained by those skilled in the art without any creative effort based on these drawings.

[0028] Figure 1 A flow chart of the method for strengthening plant remediation of cadmium contaminated soil by using degradable chelating agents is shown;

[0029] Figure 2 A box structure schematic diagram of the method for strengthening plant remediation of cadmium contaminated soil by using degradable chelating agents is shown.

[0030] Marked explanation:

[0031] 1-removable partition, 2-gravel layer, 3-coarse sand and gravel mixed layer, 4-adsorption material layer, 5-cadmium contaminated soil layer to be remediated, 6-spraying device, 7-peristaltic pump, 8-leaching solution. DETAILED DESCRIPTION

[0032] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way limiting on the application or its applications or uses. Based on the embodiments in the present application, any product that is the same or similar to the present application obtained by anyone under the inspiration of the present application or by combining the present application with other prior art features falls within the protection scope of the present application. In addition, all other embodiments obtained by those of ordinary skill in the art without carrying out creative labor fall within the protection scope of the present application.

[0033] If the specific experimental steps or conditions are not specified in the embodiments, the operation or conditions can be carried out according to the conventional experimental steps described in the prior art in the field. If the manufacturers of the reagents and other instruments are not specified, the reagents are conventional reagent products that can be obtained from the market. In addition, the drawings are only schematic illustrations of the embodiments of the present application, and are not necessarily drawn to scale. The same reference numerals in the drawings represent the same or similar parts, and thus repeated description thereof will be omitted. Some block diagrams shown in the drawings are functional entities, and do not necessarily correspond to physically or logically independent entities.

[0034] The techniques, methods, and devices known to those of ordinary skill in the relevant art can not be discussed in detail, but under appropriate circumstances, the techniques, methods, and devices should be considered as part of the authorized description.

[0035] In addition, the technical features involved in different embodiments of the present application described below can be combined with each other as long as they do not conflict with each other.

[0036] The prior art has problems such as low repair efficiency, easy pollution of cadmium-containing waste liquid to groundwater, long residual time of chelating agent used, and secondary pollution when using plants to repair cadmium-contaminated soil. The present application selects torch poinsettia seedlings with strong enrichment ability for cadmium metal, plants them in the cadmium-contaminated soil layer to be repaired, and sprays a specially prepared green degradable composite chelating agent in several times during the growth cycle to promote the activation and release of cadmium in the contaminated soil layer, strengthen the extraction efficiency of cadmium by torch poinsettia, and promote the growth of torch poinsettia. In addition, the present application builds a gravel layer, a coarse sand and gravel mixed layer, and an adsorption material layer below the contaminated soil layer, effectively preventing the migration of cadmium pollutants to groundwater and avoiding the problem of secondary pollution.

[0037] The specific implementation is as follows:

[0038] In a first aspect, the present application provides a method for strengthening plant repair of cadmium-contaminated soil by using degradable chelating agent,Figure 1 A flow chart of a method for degradable chelating agent reinforced phytoremediation of cadmium contaminated soil is shown, and the method comprises the following steps:

[0039] S1, prepare a coverless box, and set a detachable partition plate at a distance of 100-300 mm from the bottom of the box, and sequentially lay a gravel layer, a coarse sand and gravel mixed layer, an adsorption material layer, and a cadmium concentration of 2-10 mg / kg of the cadmium contaminated soil layer to be remediated above the detachable partition plate.

[0040] In the specific implementation of this step, first, select the appropriate filler layer material and laying thickness as the filter layer, which can adsorb cadmium pollutants in the leachate, effectively prevent the penetration of treated cadmium pollutants into the groundwater layer, and prevent secondary pollution. The thickness of the gravel layer is 20-200 mm, the thickness of the coarse sand and gravel mixed layer is 20-200 mm, the thickness of the adsorption material layer is 20-200 mm, and correspondingly, the thickness of the cadmium contaminated soil layer is 50-500 mm. A geotextile with a weight of 400 g / m 2 is used to lay between each layer to ensure that the upper leachate passes through in sequence while preventing the loss of the cadmium contaminated soil to be treated for the experiment. The detachable partition plate is provided with holes for the outflow of the leachate to facilitate the collection of the leachate, and the hole diameter of the holes is 10 mm, and the spacing between adjacent holes is 50 mm.

[0041] S2, transplant the cultivated torch comb seedlings into the cadmium contaminated soil layer to be remediated, and spray the composite chelating agent on the 1st day, the 15th day, and the 30th day to enhance the extraction efficiency of the plant for cadmium in the cadmium contaminated soil layer to be remediated; collect the leachate and determine the concentration of cadmium.

[0042] In the specific implementation of this step, the same soil as the source of the cadmium contaminated soil layer to be remediated is laid in a constant temperature incubator at 20°C, and then torch com is seeded or cut in the soil to obtain the cultivated torch comb seedlings, and the height of the cultivated torch comb seedlings is 10-15 cm. Then, the cultivated torch comb seedlings are transplanted into the cadmium contaminated soil layer to be remediated, and the composite chelating agent is sprayed on the 1st day, the 15th day, and the 30th day to enhance the extraction efficiency of the plant for cadmium in the cadmium contaminated soil layer to be remediated. A small amount of leachate produced after the composite chelating agent leaching is collected, and the content of cadmium is determined. The composite chelating agent is prepared by mixing 0.1-0.5 mol / L polyglutamic acid (γ-PGA) and 0.05-0.2 mol / L hexanediamine tetramethylene phosphonic acid (HDTMPA) in a volume ratio of 1-4:1. The concentration of each component in the composite chelating agent is selected considering the input cost, the purification effect that can be promoted, and the tolerance of the plant. The single spraying amount of the composite chelating agent is 3-5 L / m2 .

[0043] HDTMPA is a novel organophosphonic acid chelating agent that readily chelates metal ions. Its complexing ability is stronger than that of EDTA, and its complexing stability constant is larger. The complex formed is not easily dissociated, exhibits excellent chemical stability, and is readily biodegradable.

[0044] γ-PGA is widely found in the environment. It is a biodegradable, non-toxic, and multifunctional biopolymer characterized by hydrogen bonding, structural functionality, and polyanionic properties. Based on the amide bond formed by the α-NH2 and γ-COOH groups in its backbone, γ-PGA can effectively promote soil aggregate formation, protect soil fertility, regulate microbial community structure, and enhance plant antioxidant capacity. Furthermore, γ-PGA can better transport nutrients and water from the soil to plants, thereby promoting better plant growth. γ-PGA can also absorb nutrients from fertilizers and deliver them to plants, improving fertilizer conversion and utilization. Furthermore, given the complex composition of soil, γ-PGA can prevent precipitation caused by chemical reactions between certain acid ions and metal elements, promote plant root development, and enhance plant disease resistance. Furthermore, polyglutamic acid can bind toxic heavy metals, forming dissolved complexes with them and increasing their active ingredients in the soil solution. Polyglutamic acid also promotes the absorption and utilization of trace elements and phosphate fertilizers. In addition, polyglutamic acid can also improve the cation exchange capacity of the soil, temporarily store trace elements such as calcium and magnesium and other adsorbed cations, and then slowly replenish them in the soil.

[0045] The composite chelating agent, derived from a combination of HDTMPA and γ-PGA, effectively binds to heavy metal ions in the soil, converting heavy metal compounds into ions. This increases the concentration of heavy metal ions in the soil solution and facilitates their absorption by the broodstock. The composite chelating agent also acts as a growth-promoting fertilizer and regulator. This dual-action effect allows the broodstock to more efficiently absorb ionic heavy metals during growth, thereby reducing the concentration of heavy metals in the soil and completing soil heavy metal remediation.

[0046] S3. Collect mature Celosia pyralis plants, shake off the soil adhering to the roots as rhizosphere soil, and measure the cadmium concentration of the rhizosphere soil; rinse the Celosia pyralis plants thoroughly, wither at 100-110°C for 30-90 minutes, then dry at 70°C to constant weight, crush, digest with nitric acid, and measure the cadmium concentration in the digestion solution using a mass spectrometer.

[0047] During the specific implementation of this step, mature Torch Cockscomb plants are collected, and the soil adhering to the roots is shaken off as rhizosphere soil. The rhizosphere soil is dried at 70°C and crushed through a 100-mesh sieve. A mixture of perchloric acid, hydrofluoric acid, and nitric acid is used for digestion, and the cadmium concentration of the digestion solution is measured using a mass spectrometer to calculate the cadmium enrichment in the roots. The Torch Cockscomb plants are then divided into roots and aerial parts, thoroughly rinsed, and cured at 100-110°C for 30-90 minutes. They are then dried at 70°C to constant weight, crushed, digested using nitric acid, and the cadmium concentration in the digestion solution is measured using a mass spectrometer. Preferably, the curing temperature is 105°C and the time is 30 minutes.

[0048] Preferably, when the cadmium concentration of the cadmium-contaminated soil layer to be repaired is 10 mg / kg, correspondingly, the composite chelating agent is made by mixing 0.5 mol / L polyglutamic acid (γ-PGA) and 0.2 mol / L hexamethylenediaminetetramethylenephosphonic acid (HDTMPA) in a volume ratio of 1:1, the thickness of the gravel layer is 100 mm, the thickness of the coarse gravel mixed layer is 100 mm, the thickness of the adsorption material layer is 100 mm, and the thickness of the cadmium-contaminated soil layer to be repaired is 300-500 mm, the composite chelating agent not only promotes the growth of torch comb, but also promotes the activation and release of cadmium, especially improves the extraction efficiency of torch comb for cadmium. Specifically, the enrichment coefficient of torch comb can reach 1.35, and the transfer coefficient can reach 1.43.

[0049] The present invention provides a method for strengthening plant remediation of cadmium-contaminated soil using a degradable chelating agent. The method comprises selecting seedlings of Cockscomb with a strong ability to enrich cadmium metal and planting them in the cadmium-contaminated soil layer to be repaired. The seedlings are sprayed with a special green degradable composite chelating agent in batches during the growth cycle to promote the activation and release of cadmium in the cadmium-contaminated soil layer to be repaired, thereby enhancing the extraction efficiency of Cockscomb for cadmium and promoting the growth of Cockscomb. The method has low remediation cost and is environmentally friendly. It is particularly suitable for soil contaminated with medium and high concentrations of cadmium and can further improve soil fertility. Generally, only a few growth cycles are needed to reduce the total amount of heavy metals and the effective state content to an ideal state. In practical applications, the present invention can prevent pollutants from migrating through wind erosion, water erosion, leaching and soil diffusion by establishing a plant cover layer on the surface of the contaminated site.

[0050] In order to enable those skilled in the art to more clearly understand the present invention, the method of the present invention for enhancing phytoremediation of cadmium-contaminated soil by using a degradable chelating agent is now described in detail through the following examples.

[0051] Example 1

[0052] Ten experimental groups were set up in this embodiment, and the chelating agents used in the ten experimental groups were different, and other experimental conditions were consistent. Table 1 shows the setting of chelating agents in different experimental groups. H0 is a blank control group, and no chelating agent is added. H1-H3 use a single chelating agent, which is HDTMPA at different concentrations. P1-P3 use a single chelating agent, which is γ-PGA at different concentrations. M1-M3 use a special composite chelating agent of the present application, which is HDTMPA and γ-PGA mixed in equal volumes at different concentrations.

[0053] S1, build a plant repair box. Figure 2 The box structure diagram for extracting cadmium in soil by plants is shown in the figure. A rectangular box without a cover is prepared, and the five surfaces are sealed, and the top is open. The box structure is made of transparent acrylic material, and the sealing is good. A detachable partition plate 1 is arranged 100 mm away from the bottom of the box. The detachable partition plate 1 is provided with holes, and the hole diameter of the holes is 10 mm. The distance between adjacent holes is 50 mm. The space above the detachable partition plate 1 is sequentially laid with a gravel layer 2, a coarse sand and gravel mixed layer 3, an adsorption material layer 4, and a cadmium contaminated soil layer 5 to be repaired from bottom to top. The geotextile with a thickness of 400 g / m 2 The heavy metal form added in the cadmium contaminated soil layer 5 to be repaired is CdCl2, which is added to the soil in a solid state and mixed thoroughly. The Cd addition concentration is 10 mg / kg. The thickness of the gravel layer is 100 mm, the thickness of the coarse sand and gravel mixed layer is 100 mm, the thickness of the adsorption material layer is 100 mm, and the thickness of the cadmium contaminated soil layer is 300-500 mm. The surface of the cadmium contaminated soil layer 5 to be repaired is uniformly laid with a spraying device 6, and the spraying device 6 is connected with a peristaltic pump 7 for continuously and uniformly adding a composite chelating agent to the cadmium contaminated soil during the growth cycle of the plants.

[0054] S2, the soil with the same source as the cadmium contaminated soil layer 5 to be repaired is laid in a constant temperature incubator at 20°C, and then torch cockscomb seeds are sown in the soil for cultivation to obtain torch cockscomb seedlings with a height of 10-15 cm. The cultivated torch cockscomb seedlings are transplanted into the cadmium contaminated soil layer 5 to be repaired in the box, and the composite chelating agent and the single chelating agent are sprayed on the first day, the fifteenth day, and the thirtieth day, respectively. The leachate 8 at the bottom of the box is collected, and the cadmium concentration is determined by inductively coupled plasma mass spectrometry (iCAPQ, Thermo Fisher Scientific Instruments Co., Ltd., USA);

[0055] S3, Torch Comb Growth for Three Months, Harvest, Collect Mature Torch Comb Plants, Shake off the Soil Adhered to the Roots as Rhizosphere Soil, Dry the Rhizosphere Soil at 70°C, Crush through a 100-mesh Screen, Digest with a Mixed Solution of Perchloric Acid, Hydrofluoric Acid and Nitric Acid, Then Measure the Cadmium Concentration of the Digestion Solution with a Mass Spectrometer to Calculate the Cadmium Enrichment Degree of the Roots. Divide the Torch Comb Plants into Roots and Aboveground Parts, Rinse Thoroughly, Kill Green at 105°C for 30 min, Then Dry at 70°C to Constant Weight, Crush, Digest with Nitric Acid, and Measure the Cadmium Concentration in the Digestion Solution with an Inductively Coupled Plasma Mass Spectrometer (iCAPQ, Thermo Fisher Scientific Instruments Co., Ltd.).

[0056] Calculation Method: Enrichment Coefficient (EC) = Cd Concentration in Plant Aboveground Part / Cd Concentration in Rhizosphere Soil;

[0057] Transfer Factor (TF) = Cd Concentration in Plant Aboveground Part / Cd Concentration in Plant Roots;

[0058] Tolerance Index = Dry Weight of Plants in Treatment Group / Dry Weight of Plants in Control Group.

[0059] Table 1 Chelating Agent Settings for Experimental Groups

[0060] Treatment Chelator content B0 Blank control H1 0.05 mol / L HDTMPA H2 0.1 mol / L HDTMPA H3 0.2 mol / L HDTMPA P1 0.1 mol / L γ-PGA P2 0.3 mol / L γ-PGA P3 0.5 mol / L γ-PGA M1 0.05 mol / L HDTMPA and 0.1 mol / L γ-PGA mixed in equal volume M1 0.10 mol / L HDTMPA and 0.3 mol / L γ-PGA mixed in equal volume M3 0.2 mol / L HDTMPA and 0.5 mol / L γ-PGA mixed in equal volume

[0061] Table 2 Remediation Efficiency of Torch Comb Treated with Different Chelating Agents for Cd Contaminated Soil

[0062]

[0063] Table 2 shows the remediation efficiency of Cd contaminated soil by torch chicken with different chelating agent treatment. As shown in the table, the biomass of torch chicken with single chelating agent (H3, HDTMPA) of 0.2 mol / L is lower than that of B0 group, mainly because HDTMPA promotes the activation of heavy metal ions in rhizosphere, and the growth of torch chicken is inhibited under Cd stress. Within the concentration range of the test, γ-PGA significantly increases the tolerance index of torch chicken. It is generally believed that the enrichment coefficient and transfer coefficient of hyperaccumulator are both greater than 1, and both the enrichment coefficient and transfer coefficient are high to indicate that the purification efficiency of the plant to Cd is high. It can be seen that the enrichment coefficient of torch chicken to Cd is less than 1 when HDTMPA is applied alone. When γ-PGA is applied alone, the transfer coefficient and enrichment coefficient of torch chicken to Cd are both less than 1. Therefore, the application of HDTMPA and γ-PGA as chelating agents alone cannot effectively improve the purification efficiency of torch chicken to Cd. When the composite chelating agent mixed with equal volume of HDTMPA and γ-PGA is applied, the transfer coefficient and enrichment coefficient are both greater than 1, which indicates that the remediation efficiency of Cd-containing soil by applying the composite chelating agent solution is significantly higher than that of applying a single chelating agent. When the composite chelating agent obtained by mixing equal volume of 0.2 mol / L HDTMPA and 0.5 mol / L γ-PGA is sprayed, the enrichment coefficient can reach 1.35, the transfer coefficient can reach 1.43, and the purification efficiency is optimal.

[0064] In the description of the present specification, the description of the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" and the like means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in the specification.

[0065] For the method embodiments, in order to simply describe, they are all expressed as a series of action combinations, but those skilled in the art should know that the present application is not limited by the order of the described actions, because according to the present application, certain steps can be performed in other order or simultaneously. Secondly, those skilled in the art should know that the embodiments described in the specification are all preferred embodiments, and the actions and components involved are not necessarily necessary for the present application.

[0066] The method for using the degradable chelating agent to strengthen the plant remediation of the cadmium contaminated soil is described in detail, the principle and implementation mode of the application are described by using specific examples, the above description of the examples is only used for helping understanding the method and the core idea of the application; meanwhile, for the general technical personnel in the art, according to the idea of the application, the specific implementation mode and the application range can be changed, and the above description should not be understood as the limitation of the application.

Claims

1. A method for enhancing phytoremediation of cadmium-contaminated soil using a degradable chelating agent, characterized in that: The method comprises the following steps: S1. Prepare an uncovered box with a removable partition 100-300 mm from the bottom of the box. In the space above the removable partition, lay a crushed stone layer, a coarse gravel mixed layer, an adsorption material layer, and a cadmium-contaminated soil layer to be remediated with a cadmium concentration of 2-10 mg / kg in sequence from bottom to top. S2. Transplanting the cultivated Cockscomb seedlings into the cadmium-contaminated soil layer to be repaired, and spraying the composite chelating agent on the 1st day, the 15th day, and the 30th day, respectively, to enhance the plant's efficiency in extracting cadmium from the cadmium-contaminated soil layer to be repaired; Collect the leachate and determine the cadmium concentration; S3. Collect mature Celosia pyralis plants, shake off the soil adhering to the roots as rhizosphere soil, and measure the cadmium concentration of the rhizosphere soil; rinse the Celosia pyralis plants thoroughly, fix them at 100-110° C. for 30-90 min, then dry them at 70° C. to constant weight, crush them, digest them with nitric acid, and measure the cadmium concentration in the digestion solution using a mass spectrometer; The thickness of the crushed stone layer is 20-200 mm, the thickness of the coarse gravel mixed layer is 20-200 mm, the thickness of the adsorption material layer is 20-200 mm, and the thickness of the cadmium contaminated soil layer is 50-500 mm. The composite chelating agent is prepared by mixing 0.1-0.5 mol / L of polyglutamic acid (γ-PGA) and 0.05-0.2 mol / L of hexamethylenediaminetetramethylenephosphonic acid (HDTMPA) in a volume ratio of 1-4:

1.

2. The method according to claim 1, characterized in that The composite chelating agent is prepared by mixing 0.5 mol / L polyglutamic acid (γ-PGA) and 0.2 mol / L hexamethylenediaminetetramethylenephosphonic acid (HDTMPA) in a volume ratio of 1:

1.

3. The method according to claim 1, characterized in that The single spraying dosage of the composite chelating agent is 3-5L / m 2 .

4. The method according to claim 1, wherein The thickness of the crushed stone layer is 100 mm, the thickness of the coarse gravel mixed layer is 100 mm, and the thickness of the adsorption material layer is 100 mm.

5. The method according to claim 1, wherein The thickness of the cadmium-contaminated soil layer to be repaired is 300-500 mm.

6. The method according to claim 1, characterized in that The cadmium concentration of the cadmium-contaminated soil layer to be repaired is 10 mg / kg.

7. The method according to claim 1, characterized in that The cultivated torch cockscomb seedlings are obtained by the following method: Soil from the same source as the cadmium-contaminated soil layer to be repaired is laid in a constant temperature incubator at 20°C, and then Torch Cockscomb is sown or cut into the soil to obtain the cultivated Torch Cockscomb seedlings; the height of the cultivated Torch Cockscomb seedlings is 10-15cm.

8. The method according to claim 1, characterized in that The detachable partition is provided with holes, the hole diameter of the holes is 10 mm, and the spacing between adjacent holes is 50 mm.

9. The method according to claim 1, characterized in that The cadmium concentration of the rhizosphere soil was determined by the following method: The rhizosphere soil was dried at 70° C. and then pulverized and passed through a 100-mesh sieve. The soil was digested with a mixture of perchloric acid, hydrofluoric acid, and nitric acid, and the cadmium concentration of the digested solution was measured using a mass spectrometer.

10. The method according to claim 1, characterized in that The temperature of the fixing is 105° C. and the time is 30 minutes.

Images