CN111909703A - In-situ remediation agent for low-level heavy metal pollution in facility vegetable fields, preparation and application methods - Google Patents

Abstract

The invention provides an in-situ restoration agent for low-degree heavy metal contaminated soil of a facility vegetable field, and a preparation method and an application method thereof, belonging to the technical field of in-situ restoration of soil. The invention mainly aims at the characteristic of low heavy metal pollution intensity of facility vegetable fields in China, and provides the special in-situ restoration agent for the low heavy metal pollution facility vegetable field soil, which has the advantages of rich raw materials, low cost, simple production process, high restoration efficiency and no secondary pollution, and the preparation and application methods thereof.

Description

In-situ remediation agent for low-level heavy metal pollution in facility vegetable fields, preparation and application methods

technical field

The invention relates to the technical field of soil in-situ remediation, in particular to an in-situ remediation agent for low-level heavy metal-contaminated soil in facility vegetable fields and a preparation and application method thereof.

Background technique

The current situation of heavy metal pollution in farmland soil in some areas of my country is relatively serious, resulting in excessive heavy metal content in agricultural products and endangering human health. At the same time, my country has more people and less land. In order to ensure food security, it is still necessary to safely utilize moderately and slightly polluted farmland and produce safe agricultural products. In 2016, the State Council issued the Action Plan for the Prevention and Control of Soil Pollution, requiring that by 2020 and 2030, the safe utilization rate of contaminated farmland should reach about 90% and over 95%, respectively. Therefore, the restoration and control of heavy metals in moderately and lightly polluted farmland soil has become a hot spot in agricultural environmental research in recent years.

Soil heavy metal pollution refers to the pollution caused by excessive accumulation of heavy metals in soil. Heavy metals polluting soil include elements with significant biological toxicity such as Cd, Pb, Hg, Cr, As, and elements with certain toxicity such as Cu, Zn, and Ni. This type of pollution has a wide range, long duration, hidden pollution, and cannot be biodegraded, which will lead to soil degradation, decline in crop yield and quality, and contaminate surface water and groundwater through runoff and leaching.

The Ministry of Environmental Protection of the People's Republic of China has sampled and monitored the soil of 300,000 hectares of basic farmland protected areas, and found that 36,000 hectares of soil have exceeded the standard for heavy metals, with an exceeding rate of 12.1%. According to the Ministry of Land and Resources, more than 10% of the country's arable land has been polluted by heavy metals, about 150 million mu, 32.5 million mu of arable land has been polluted by sewage irrigation, and 2 million mu of solid waste has been accumulated and destroyed, most of which are concentrated in economically developed areas.

The remediation technologies for heavy metal-contaminated soil can be classified into two categories: one is to use engineering measures and plant extraction methods to remove heavy metal pollutants from the soil, but engineering measures (such as soil removal, soil replacement, etc.) are not suitable for large areas and low pollution intensity. However, the efficiency of phytoremediation is low and the cycle is long. Especially in our country, there are more people and less arable land. It is impossible to completely stop the production of food on the existing arable land, and use phytoremediation technology for long-term treatment; the second category is In-situ passivation repair technology mainly changes the form of heavy metals in soil by adding passivating agents, reducing the mobility and bioavailability of heavy metals, thereby reducing the absorption of heavy metals by plants. In view of the basic situation of heavy metal pollution in China's farmland, the pollution area is large but the pollution degree is not high, such as the general total Cd content ≦ 1.0 mg k ^-1 , the total Pb content ≦ 500 mg kg ^-1 , so the practical soil remediation agent, passivation The activity of heavy metal ions in the soil, preventing and controlling the transfer and enrichment of heavy metal ions by crops, and achieving the purpose of safe production, this technology has great practical significance.

The traditional fixed substances mainly use phosphate, lime and biosolids as materials, which are expensive and have a significant effect on single heavy metal-contaminated soil during the remediation process, but not on the pollution phenomenon associated with several elements. The traditional fixative has a single component, and has poor buffering performance in the soil. When the soil conditions change, the stability is affected, and the soil nutrients cannot be replenished in time during the restoration process.

Shrimp and crab shells are by-products of marine fisheries. The main inorganic components are calcium carbonate and chitin, and they have a unique microstructure of biological evolution. However, at present, the utilization of shrimp and crab shells is limited, and most of them are treated as garbage, which has potential harm to the environment over time and a serious waste of resources; some methods of recycling crab shells only use the calcium carbonate in the crab shells. Converting hydroxyapatite, or converting chitosan only with chitin as an active ingredient, cannot make full use of the active ingredients in crab shells. If the calcium carbonate and chitin in the crab shells can be simultaneously utilized through a simple and effective conversion method, and the protein and oil remaining in the shrimp and crab shells can be effectively recycled, the pollution to the environment can be reduced, and the resource utilization can be realized. Effective use to achieve green environmental protection.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide an in-situ remediation agent for low-level heavy metal-contaminated soil in facility vegetable fields, mainly aiming at the characteristics of low heavy metal pollution intensity in facility vegetable fields in my country, and proposes a kind of rich raw materials, low cost, simple production process, high repair efficiency, no The invention relates to a preparation method and an application method of a special soil remediation agent for vegetable soil in a low heavy metal pollution facility with secondary pollution.

The first object of the present invention is to provide an in-situ repair agent for low-level heavy metal contaminated soil of facility vegetables, which is prepared by mixing, heating, reacting, and drying shrimp and crab shell extracts and alum pulp powder.

As a further technical solution, the shrimp and crab shell extracts are prepared from shrimp shells and crab shells through acid washing and alkaline washing processes in sequence.

The second object of the present invention is to provide a preparation method of an in-situ remediation agent for low-level heavy metal-contaminated soil in facility vegetable fields,

(1) Preparation of alum slurry powder;

(2) Preparation of shrimp and crab shell extract

A1, pretreatment, remove impurities such as meat and dirt from shrimp and crab shells, wash with water, and dry;

A2, pickling process, the pretreated shrimp and crab shells are placed in dilute hydrochloric acid for reaction, and then filtered and washed to neutrality;

A3, alkaline washing process, the shrimp and crab shells after pickling are placed in sodium hydroxide solution to react;

A4, filter, wash to neutrality, and then dry to obtain the solid state described shrimp and crab shell extract;

(3) Mixed heating reaction

S1: mixing the shrimp and crab shell extract described in step (2) with water and acid, and under nitrogen protection, the reaction temperature is controlled to be 40-60° C. and continuously heated for 1.5-3h;

S2: add H ₂ O ₂ after the S1 reaction finishes;

S3: then add the alum slurry powder prepared in step (1), and fully stir to make a paste;

S4: standing overnight, suction filtration, and vacuum drying to constant weight to prepare the repairing agent.

As a further technical solution,

In the pickling process, the concentration of hydrochloric acid is 5%-10%, and it is soaked at room temperature for 2-4h.

As a further technical solution,

The alkaline washing process specifically includes placing the pickled shrimp and crab shells in a 10% sodium hydroxide solution and boiling at 100±5° C. for 2 hours.

As a further technical solution, the step (3) is as follows:

S1: Mix 1 g of the shrimp and crab shell extract described in step (2) with 100 ml of deionized water and 1 mL of acid, and under nitrogen protection, control the reaction temperature to be 50 ° C and continue heating for 2 h;

S2: add 20 ml of 30% H ₂ O ₂ after the S1 reaction finishes;

S3: then add 20g of the alum slurry powder prepared in step (1), and fully stir to make a paste;

S4: standing overnight, suction filtration, and vacuum drying to constant weight to prepare the repairing agent.

As a further technical solution, the specific steps of the step (1) are as follows: the alum slurry is dried and ground, then placed in a muffle furnace and heated to 800°C at a constant speed of 5°C min ^-1 , and naturally cooled after calcining for 1-2 hours. , washed with water until neutral, dried, ground and passed through an 80-mesh sieve to obtain the alum slurry powder.

The third object of the present invention is to provide a method for applying an in-situ remediation agent for low-level heavy metal-contaminated soil in a facility vegetable field: it includes the remediation agent prepared by the above method, and after the soil to be rehabilitated is harvested and the vegetables are harvested, the above-mentioned remediation agent is applied. Apply 50-100 kg/mu to the surface, deep plough, water, and keep the soil moist for 2 weeks, then the crops can be planted and managed according to conventional methods, and no chemical fertilizers can be applied during the application of the repair agent.

Compared with the prior art, the in-situ remediation agent for low-level heavy metal contaminated soil in facility vegetable fields provided by the present invention and its technical advantages are as follows:

The in-situ repairing agent for low-level heavy metal polluted soil in facility vegetable fields provided by the invention can repair the Cd content in the polluted soil not more than 1.0 mg/kg, and the Pb content in the range of not more than 500 mg/kg.

The in-situ remediation agent for low-level heavy metal contaminated soil in facility vegetable fields provided by the invention has good remediation effect, and the invention is an exogenous substance added to the contaminated soil to reduce the bioavailability of heavy metals in the soil; specifically, it is a heavy metal contaminated soil In in situ remediation technology, it is a fixative to reduce the mobility of metal ions in soil and reduce their toxicity to organisms. After the exogenous additives are put into the soil, on the one hand, they can change the migration and activation properties of metal ions by affecting the pH value in the soil environment; on the other hand, they can capture free metals from the soil environment through the physical and chemical properties of the fixative itself. ions, which adsorb and fix metal ions in additives and generate new conformations. Thereby, the remediation effect of passivating the activity of metal ions and reducing their migration from the soil environment to plants and groundwater systems is achieved; it has a good effect on the non-point source pollution of agricultural soil pollution.

The in-situ remediation agent for low-level heavy metal-contaminated soil in facility vegetable fields provided by the invention has low cost. The present invention adopts a synthetic method, uses organic and inorganic materials as carriers, and produces a mixture after modification. The fixing agent produced by the invention has low synthesis cost, wide material sources and easy acquisition, stable and reliable preparation process, and is suitable for the treatment of different types of heavy metal polluted soil, and the input is low.

The in-situ remediation agent for low-level heavy metal-contaminated soil in facility vegetable fields provided by the invention has a wide application range. The fixing agent of the invention is mainly used in the in-situ restoration process of heavy metal polluted soil, can be used in a large area of agricultural soil, has a significant effect on compound pollution caused by different heavy metal elements, and has the advantages of low price, no secondary pollution, Environmentally friendly and so on.

The in-situ remediation agent for the low-level heavy metal polluted soil of the facility vegetable field provided by the invention has high remediation efficiency. The fixing agent of the invention has a large adsorption capacity for various heavy metal ions and a wide range of application environments, and especially has the effect of fixing various metal ions at the same time; the agricultural straw is used as the organic carrier of the fixing agent, and can be used as an auxiliary in the repair process at the same time. It has the effect of adsorption and fixation, and can replenish a large amount of nutrients to the soil in time, and supplement the fertility of the soil environment.

Description of drawings

Fig. 1 is a process flow diagram of the present invention.

Fig. 2 is a process flow diagram for preparing the shrimp and crab shell extract in Fig. 1 .

Figure 3 shows the heavy metal Cd and Pb content (mg/kg) in the edible part of vegetables without the addition of repair agent.

Figure 4 shows the content (mg/kg) of heavy metals Cd and Pb in the edible part of vegetables added with repair agent.

Fig. 5 Dry weight of biomass (g/pot) of each organ of Amaranth with different treatments.

Fig. 6 Cd content (mg/kg) in aerial parts of green-leaf amaranth with different treatments.

Detailed ways

The present invention will be further described in detail below through specific embodiments and in conjunction with the accompanying drawings.

Example 1

The utility model relates to an in-situ repairing agent for low-level heavy metal-contaminated soil in facility vegetable fields. The repairing agent is prepared by mixing, heating, reacting, and drying shrimp and crab shell extracts and alum pulp powder. The shrimp and crab shell extract is prepared by using shrimp shell and crab shell as raw materials, and sequentially undergoing acid washing and alkali washing processes.

A method for preparing an in-situ remediation agent for low-level heavy metal-contaminated soil in facility vegetable fields, the method comprising the following steps:

(1) Preparation of alum slurry powder;

(2) Preparation of shrimp and crab shell extract;

A1, pretreatment, remove impurities such as meat and dirt from shrimp and crab shells, wash with water, and dry;

A2, pickling process, the pretreated shrimp and crab shells are placed in dilute hydrochloric acid for reaction, and then filtered and washed to neutrality;

A3, alkaline washing process, the shrimp and crab shells after pickling are placed in sodium hydroxide solution to react;

A4, filter, wash to neutrality, and then dry to obtain the solid state described shrimp and crab shell extract;

(3) Mixed heating reaction

S1: mixing the shrimp and crab shell extract described in step (2) with water and acid, and under nitrogen protection, the reaction temperature is controlled to be 40-60° C. and continuously heated for 1.5-3h;

S2: add H ₂ O ₂ after the S1 reaction finishes;

S3: then add the alum slurry powder prepared in step (1), and fully stir to make a paste;

S4: standing overnight, suction filtration, and vacuum drying to constant weight to prepare the repairing agent.

As a further technical solution, in the pickling process, the concentration of hydrochloric acid is 5%-10%, and the solution is soaked at room temperature for 2-4 hours.

As a further technical solution, the alkaline washing process specifically includes placing the acid-washed shrimp and crab shells in a 10% sodium hydroxide solution and boiling at 100±5° C. for 2 hours.

As a further technical solution, the step (3) is as follows:

S1: Mix 1 g of the shrimp and crab shell extract described in step (2) with 100 ml of deionized water and 1 mL of acid, and under nitrogen protection, control the reaction temperature to be 50 ° C and continue heating for 2 h;

S2: add 20 ml of 30% H ₂ O ₂ after the S1 reaction finishes;

S3: then add 20g of the alum slurry powder prepared in step (1), and fully stir to make a paste;

S4: standing overnight, suction filtration, and vacuum drying to constant weight to prepare the repairing agent.

As a further technical solution, the specific steps of the step (1) are as follows: the alum slurry is dried and ground, then placed in a muffle furnace and heated to 800°C at a constant speed of 5°C min ^-1 , and naturally cooled after calcining for 1-2 hours. , washed with water until neutral, dried, ground and passed through an 80-mesh sieve to obtain the alum slurry powder.

Example 2: The effect of applying in-situ repairing agent in the field to produce cherry tomato

In conjunction with embodiment 1, the application method of the in-situ remediation agent for low-level heavy metal pollution soil in facility vegetable fields: after harvesting the vegetables in the soil to be rehabilitated, the remediation agent is applied to the soil of the facility vegetable greenhouse by 50 kilograms/mu consumption, Deep plowing, watering, and keeping the soil moist for 2 weeks, and no fertilizers during application of the restorer. After two weeks, crops can be planted and managed according to conventional methods, and cherry tomatoes can be planted. The experimental results show that the heavy metals (Cd, Pb, Zn, Cu, Ni) in cherry tomato fruits are all lower than the limit values of food pollutants in China (food pollutants). The limit standard for medium pollutants (GB2762-2012) achieves the purpose of safe production.

Example 3: The effect of applying in-situ repairing agent in the field to produce cucumber

In conjunction with embodiment 1, the application method of the low-level heavy metal pollution soil in-situ remediation agent in the facility vegetable field: after the soil to be rehabilitated is harvested as the stubble vegetables, the remediation agent is applied to the facility vegetable greenhouse of planting cucumber by 80 kg/per mu consumption. In the soil, plough deeply, water, and keep the soil moist for 2 weeks, and do not apply chemical fertilizers during the application of the repair agent. After two weeks, crops can be planted and managed according to conventional methods, and cucumbers can be planted. The experimental results show that the heavy metals (Cd, Pb, Zn, Cu, Ni) in cucumbers are all lower than the standard value of Chinese food contaminants (contaminants in food). Limited standard GB2762-2012) to achieve the purpose of safe production.

Example 4: Comparative test of applying the repairing agent in the invention and not applying the passivating agent

Experiments were carried out in pots in a greenhouse. The pots used in the experiment were PVC pots with a diameter of 30 cm and a height of 30 cm. The bottom of the pot was cushioned with a 20-mesh nylon mesh to prevent soil leakage, and 12 kg (dry weight) of soil was loaded. The contents of Cd and Pb in the soil were 0.54 mg/kg and 358 mg/kg, respectively. According to the soil environmental quality standard, they belonged to the second type of soil (the Cd content was 0.38 mg/kg and the Pb content was 376.9 mg/kg). The experimental arrangement is as follows, a total of 6 kinds of vegetables, 2 kinds of heavy metals, 1 treatment add 0.5% of the present invention's repair agent (calculated on dry soil), set up a control (without the repair agent,), unified management of the growth process, the same water and fertilizer conditions Next, 3 replicates per treatment.

Sow about 20 seeds per pot, water the soil every 1-2 d, keep the soil moist, after the seeds sprout, the first thinning is performed when the seedlings grow to about 2cm, and then the seedlings are thinned according to the growth conditions, and finally 5 plants are set. According to the length of each vegetable growth period, the edible parts were harvested successively, and the content of heavy metals in the vegetables was tested respectively. The results showed that in the treatment of adding soil remediation agent, the content of heavy metal Cd in the six vegetables, except for amaranth, all reached the level of food hygiene of heavy metal elements in vegetables in my country. Below the standard limit (0.2mg/kg), the content of heavy metal Pb all meet the food hygiene standard limit of heavy metal elements in vegetables in my country (0.3mg/kg), to achieve the purpose of safe production.

Example 5: Comparative test between applying the repairing agent in the invention and applying a conventional repairing agent (slaked lime)

In this study, the method of potted greenhouse was used to compare the effect of applying the restoration agent and lime in the invention on reducing the Cd absorption of green leaf amaranth. Experiments were carried out in pots in a greenhouse. The experiment uses PVC pots, each pot is filled with 5 kg of dry soil, and the bottom of the pot is cushioned with a 20-mesh nylon mesh to prevent soil leakage. Then, cadmium solution (3CdSO ₄ ·8H ₂ O) was added to the pot to make the Cd content in the soil 1 mg/kg, and water was added to 60% of the field water content. After that, a dry-wet cycle of watering to the field capacity and then naturally air-drying was carried out. After the soil was aged for 90 days, all the soil was poured out of the pot, the weed seeds were removed, and the pot was refilled after mixing. The soil remediation agent and slaked lime in the present invention are added at 1.0% of the total amount of soil. A control treatment (CK) without additives was set. Each treatment was repeated 4 times. Put soil remediation agent and slaked lime into the pots respectively, sow about 20 grains per pot, and then cover with soil about 1 cm. When the seedlings grow to about 2 cm, the first thinning is carried out, and then the seedlings are thinned according to the growth conditions, and 5 plants are finally set. Harvest 60 days after sowing, and collect soil samples at the same time to determine relevant parameters.

(1) Effects of different restoration agent treatments on the biomass of green leaf amaranth

The results showed that the shoot biomass of green leaf amaranth was much larger than the root biomass (Figure 2). g/pot) 4.0 times and 3.16 times. Lime application significantly decreased the biomass of green leaf amaranth. The biomass of leaves, stems and roots were 7.56 g/pot, 6.17 g/pot and 2.58 g/pot, respectively, which decreased by 44.4%, 44.9% and 27.1% compared with the control. The treatment of applying the restoration agent of the present invention has little effect on the biomass of green leaf amaranth, and the biomass of leaves and roots is similar to the control. From the observation of the growth situation, the application of lime resulted in a lighter leaf color, which affected the photosynthesis of the leaves, which in turn affected the biomass of green leaf amaranth.

(2) Effects of different treatments on Cd content in the aerial parts of green-leaf amaranth

Under the three treatments, the heavy metal Cd content in the aerial part of green leaf amaranth was leaf > stem (Fig. 3). The application of lime can greatly reduce the Cd content in green leaf amaranth leaves by 38.4%. Among them, the Cd content of green leaf amaranth leaves was 2.74 mg/kg when no lime was applied, and the Cd content was only 1.69 mg/kg with lime; /kg, a decrease of 64.7%. The application of the repairing agent in this patent can significantly reduce the Cd content in the stems and leaves of green-leaf amaranth, the Cd content in the leaves is reduced by 47.1% compared with the control, and only 1.45 mg/kg; the Cd content in the stem is reduced by 47.8% compared with the control, which is 1.15%. mg/kg.

It can be seen that the application of lime and soil remediation agent can greatly reduce the absorption of Cd by green leaf amaranth, and the decrease is more than 30% compared with the control, but the lime application reduces the biomass of green leaf amaranth by about half. The application of the restoration agent in the present invention has no obvious effect on the biomass of green leaf amaranth. Therefore, by applying the restoration agent in the present invention, the absorption of Cd by the green leaf amaranth can be effectively reduced, and the biomass of the green leaf amaranth is not affected. production losses.

Example 6

A facility vegetable field with a service life of 5 years was selected in Yuhang District, Hangzhou City, Zhejiang Province, and the surface soil (0-20cm) of the facility vegetable field and the adjacent open-air vegetable field were collected respectively to determine the content of heavy metals. The results showed that the content of heavy metals in the soil of the facility vegetable field was significant. It is higher than the adjacent open-air vegetable field (Table 1), which is slightly heavy metal-contaminated soil.

Table 1 Contents of heavy metals in the surface soil of vegetable plots and adjacent open-air vegetable plots in the test facility (mg/kg)

Cd Pb Zn Cu Facility vegetable soil 0.58 30.7 88.6 42.8 open-air vegetable soil 0.12 13.9 43.5 20.1

The surface soil of the vegetable field in the facility and the adjacent open-air vegetable field were collected and brought back to the laboratory. The soil was air-dried, crushed, mixed evenly, and then put into PVC pots for planting experiments. The slightly polluted facility vegetable soil without adding any remediation agent was recorded as treatment 1; the one planted with the surface soil of the open-air vegetable field was treatment 2, and 20 kg of the remediation agent in Example 1 of the present invention was applied per 667 square meters. The treatment was recorded as treatment 3; 40kg of the remediation agent in Example 1 of the present invention was applied to the lightly polluted vegetable field soil per 667 square meters, and the treatment was Recorded as treatment 4; 3 replicates per treatment. To ensure that all planting and management conditions are the same, 4 plants of Chinese cabbage (Shanghai Qing) were planted in each pot, and the aerial parts of the cabbage were harvested 30 days later for heavy metal content analysis.

The experimental results showed that during the whole planting process, there was no significant difference in the growth of cabbage among the treatments, and the content of heavy metals in cabbage was shown in Table 2. It can be seen from Table 2 that in treatment 1, the soil of the facility vegetable field was slightly contaminated with Cd and Pb, and the heavy metals Cd and Pb of the small greens grown in this treatment exceeded the limit values of the "Limits of Contaminants in Food" (Pb≤0.30, Cd≤ 0.20)), the content of other heavy metals does not exceed the standard; adding the repair agent of the present invention can make the heavy metal content of the aboveground parts of the small greens grown in treatment 3 and treatment 4 reach the limit value below the limit value of "Contaminant Limit in Food", to achieve safety production purpose.

Table 2 Effects of different treatments on the content of heavy metals in the aerial parts of Chinese cabbage

Cd Pb Zn Cu Process 1 Facility vegetable soil 0.211 0.351 3.078 6.037 Process 2 open-air vegetable soil 0.053 0.207 1.519 5.019 Process 3 Facility vegetable soil + repair agent 20kg 0.118 0.106 2.109 4.325 Process 4 Facility vegetable soil + repair agent 40kg 0.105 0.135 2.127 4.001

Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, but not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: The technical solutions described in the foregoing embodiments can still be modified, or some or all of the technical features thereof can be equivalently replaced; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the technical solutions of the embodiments of the present invention. scope.

Claims (8)

1. The in-situ restoration agent for the low-degree heavy metal contaminated soil of the facility vegetable field is characterized by being prepared by mixing, heating, reacting and drying shrimp and crab shell extracts and alum slurry powder.

2. The in-situ restoration agent for low-concentration heavy metal contaminated soil of facility vegetable lands as claimed in claim 1, wherein the shrimp and crab shell extract is prepared from shrimp shells and crab shells as raw materials by acid washing and alkali washing processes in sequence.

3. The preparation method of the in-situ remediation agent for the low-degree heavy metal contaminated soil of the facility vegetable field is characterized by sequentially comprising the following steps of:

preparing alum paste powder;

preparing shrimp and crab shell extract;

a1, pretreatment, removing impurities such as meat, dirt and the like of shrimp and crab shells, washing with water and drying;

a2, acid washing, namely putting the pretreated shrimp and crab shells into dilute hydrochloric acid for reaction, and then filtering and washing the shrimp and crab shells to be neutral;

a3, performing an alkali washing process, namely placing the shrimp and crab shells subjected to acid washing in a sodium hydroxide solution for reaction;

a4, filtering, washing with water to neutrality, and oven drying to obtain solid extract of shrimp and crab shell;

mixed heating reaction

S1, mixing the shrimp and crab shell extract obtained in the step (2) with water and acid, controlling the reaction temperature to be 40-60 ℃ under the protection of nitrogen, and continuously heating for 1.5-3 h;

s2 addition of H after completion of the reaction at S1₂O₂ ；

S3, adding the alum slurry powder prepared in the step (1), and fully stirring to prepare paste;

s4: standing overnight, filtering, and vacuum drying to constant weight to obtain the repairing agent.

4. The method for preparing in-situ remediation agent for low-grade heavy metal contaminated soil of facility vegetable land as claimed in claim 3, wherein the hydrochloric acid concentration in the acid pickling process is 5% -10%, and the soil is soaked at room temperature for 2-4 h.

5. The method for preparing in-situ remediation agent for low-grade heavy metal contaminated soil of facility vegetable land as claimed in claim 3, wherein the alkali washing process comprises placing the shrimp and crab shells subjected to acid washing in 10% sodium hydroxide solution, and boiling for 2h at 100 ± 5 ℃.

6. The method for preparing in-situ remediation agent for soil contaminated by low-grade heavy metals in greenhouse vegetable areas as claimed in claim 3, 4 or 5, wherein the step (3) is specifically as follows:

s1, mixing 1g of the shrimp and crab shell extract obtained in the step (2) with 100mL of deionized water and 1mL of acid, controlling the reaction temperature to be 50 ℃ under the protection of nitrogen, and continuously heating for 2 hours;

s2 addition of 20 ml of 30% H after completion of the reaction at S1₂O₂；

S3, adding 20g of alum slurry powder prepared in the step (1), and fully stirring to prepare paste;

s4: standing overnight, filtering, and vacuum drying to constant weight to obtain the repairing agent.

7. The facility vegetable low-grade weight of claim 3The preparation method of the in-situ repairing agent for the metal contaminated soil is characterized in that the step (1) comprises the following specific steps; drying Alumen pulp, grinding, and placing in muffle furnace at 5 deg.C for min^-1And raising the temperature to 800 ℃ at a constant speed, roasting for 1-2 h, naturally cooling, washing with water to be neutral, drying, grinding and sieving with a 80-mesh sieve to obtain the alum slurry powder.

8. The application method of the in-situ remediation agent for the low-degree heavy metal contaminated soil of the facility vegetable field comprises the following steps: the method is characterized in that the method comprises the repairing agent prepared by the method of any one of claims 1-7, after the current vegetable is harvested from the soil to be repaired, the repairing agent is applied to the ground surface at the dosage of 50-100 kilograms/acre, deep ploughing and watering are carried out, the soil is kept wet for 2 weeks, then the crops can be planted and managed according to the conventional method, and the fertilizer cannot be applied during the application of the repairing agent.

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