Method for repairing arsenic and cadmium polluted soil and safely producing wheat

Abstract

The invention discloses a method for repairing arsenic and cadmium polluted soil and safely producing wheat. The method comprises the following steps: 1, preparing a soil repairing agent; 2, soil slightly polluted by arsenic and cadmium is selected, and base fertilizer and the soil remediation agent prepared in the first step are evenly mixed into the soil slightly polluted by arsenic and cadmium; thirdly, sowing low-accumulation metal wheat seeds into the soil slightly polluted by arsenic and cadmium in the second step, and performing cultivation management; 4, in the wheat ripening process, the composite leaf surface blocking and controlling agent obtained in the second step is sprayed to wheat leaves for multiple times; and 5, after the wheat is mature, harvesting the wheat. The invention aims to provide a method capable of synchronously promoting the restoration of arsenic-cadmium polluted soil and the safe production of wheat so as to realize the coordination of the restoration work and the production work.

Description

Technical Field

[0001] The invention relates to the field of contaminated soil remediation, and in particular to a method for both remediating arsenic-cadmium contaminated soil and safely producing wheat. Background Art

[0002] As research on heavy metal pollution in soil deepens, humans have gradually realized that soil pollution by heavy metals such as arsenic (As) and cadmium (Cd) is mainly caused by human activities. For example, waste slag and wastewater generated after mining and smelting of ores are directly discharged into the natural environment, cadmium-containing electronic components are directly piled up and discarded in the natural environment, or arsenic-containing pesticides are used for a long time. The above human activities may cause the arsenic and cadmium content in the soil to seriously exceed the standard.

[0003] The hazards of soil contamination by arsenic and cadmium are as follows: 1. Arsenic and cadmium will inhibit the activity of soil microorganisms, destroy the decomposition of organic matter and nutrient circulation, lead to a decline in soil fertility, and cause soil function degradation; 2. Since cadmium is easily absorbed by plant roots, it interferes with the absorption of essential elements such as calcium and zinc, and arsenic will inhibit the development of plant roots and hinder photosynthesis. Therefore, it will cause the growth of some plants to be stunted, the leaves to turn yellow, or even die, affecting the ecological balance; 3. Some plants are prone to enrichment of arsenic and cadmium. When these arsenic- and cadmium-enriched crops are eaten by humans, the users may suffer from arsenic poisoning or cadmium poisoning, affecting human health.

[0004] In order to repair the land contaminated by arsenic and cadmium, the existing technology usually adopts the methods of imported soil method, chemical leaching method, phytoremediation method, chemical passivation method and the like to modify and repair the land. However, the disadvantages of the imported soil method and the chemical leaching method are high cost, long repair cycle, and the inability to guarantee the output of agricultural production while repairing the soil; the phytoremediation method uses hyperaccumulator plants to enrich and absorb arsenic and cadmium, but this method has a long repair cycle and can hardly be used for agricultural production; the chemical passivation method has relatively poor efficiency in the simultaneous adsorption of arsenic and cadmium, a long soil repair cycle, and cannot guarantee the safety of agricultural products obtained by simultaneous agricultural production. Summary of the invention

[0005] Purpose of the invention: The purpose of the present invention is to provide a method that can simultaneously promote the restoration of arsenic and cadmium contaminated soil and the safe production of wheat, thereby achieving simultaneous restoration and production.

[0006] Technical solution: The method of the present invention for simultaneously repairing arsenic-cadmium contaminated soil and safely producing wheat comprises the following steps: Step 1: Prepare soil remediation agent; Step 2: selecting soil slightly contaminated by arsenic and cadmium, and evenly mixing basal fertilizer and the soil remediation agent prepared in the first step into the soil slightly contaminated by arsenic and cadmium; Step 3: sowing seeds of low-metal-accumulating wheat in the soil slightly contaminated with arsenic and cadmium after completing the second step, and performing cultivation management; Step 4: During the wheat ripening process, spray a composite foliar inhibitor on the wheat leaves several times; Step 5: After the wheat is ripe, harvest the wheat.

[0007] Further, the steps for preparing the soil conditioner in Step 1 are as follows: (A) Grind attapulgite to 80 - 120 mesh (75 - 180 μm). After complete grinding, put it into a 1.5 mol / L hydrochloric acid (HCl) solution and soak for 2 - 4 hours (h). The volume (unit: mL) of the hydrochloric acid to the mass (unit: g) of attapulgite is 10:1. After soaking, take out the attapulgite, wash it until the pH value is neutral and then dry it to obtain acid-activated attapulgite; (B) Mix the obtained acid-activated attapulgite with deionized water No. 1. The ratio of the mass (unit: g) of the acid-activated attapulgite to the volume (unit: mL) of deionized water No. 1 is 5% - 15% to form a uniform slurry. At the same time, mix iron oxide (Fe3O4) nanoparticles with deionized water No. 2. The ratio of the mass (unit: g) of the iron oxide (Fe3O4) nanoparticles to the volume (unit: mL) of deionized water No. 2 is 1:20 - 1:30 to obtain a magnetic solution, where the mass ratio of the iron oxide (Fe3O4) nanoparticles to the mass of the acid-activated attapulgite is 1:4 - 1:6; (C) Drop the obtained magnetic solution into the slurry at a dropping rate of 0 < v ≤ 2 mL / min (v is the dropping rate of the magnetic solution). While dropping the magnetic solution, stir the slurry at a speed of 300 rpm ≤ r ≤ 800 rpm (if the stirring speed is too low, it will cause uneven mixing; if the stirring speed is too high, it may cause the slurry to splash or damage the pore structure of attapulgite). After dropping all the magnetic solution, obtain a magnetic mixture; (D) Place the magnetic mixture in a nitrogen atmosphere. Heat the nitrogen atmosphere to 300 °C at a rate of 5 °C / min, and calcine at 300 °C for 1.5 - 2.5 hours. After calcination, cool it to room temperature.

[0008] When putting attapulgite into the hydrochloric acid solution in the preparation of the soil conditioner, it is because the chloride ions (Cl) in the hydrochloric acid -It causes less damage to the silicon-oxygen framework, is suitable for retaining the pore structure, the by-products are easily soluble, the process is mature, and the effect of attapulgite acid activation is the best. If other acidic solutions such as concentrated sulfuric acid and concentrated nitric acid are used, the reactions of acidic solutions such as concentrated sulfuric acid and concentrated nitric acid are violent, and the strong oxidizing property may not only damage the framework of attapulgite, resulting in the collapse of the attapulgite structure, but also may produce by-products to block the pores. Attapulgite is soaked in hydrochloric acid for 2 to 4 hours. This time is sufficient for the acidic solution to fully react with the soluble components (such as carbonates and some silicates) in the mineral to reach kinetic equilibrium. If the soaking time is too short, the reaction may be incomplete. On the contrary, if the soaking time is too long, the silicon-oxygen framework (such as Si-O-Si bonds) may be overly damaged, resulting in structure collapse and reduction of porosity and mechanical strength.

[0009] Further, the preparation method of the iron tetroxide (Fe3O4) nanoparticles is as follows: (1) Mix ferrous chloride (FeCl2) micron particles and ferric chloride (FeCl3) micron particles in a mass ratio of 1:3, dissolve them in tertiary deionized water, and then slowly drip concentrated ammonia water with a concentration of 25% - 28% at a rate of 1 - 2 mL / min (the rate of dripping concentrated ammonia water is to control the pH value of the solution within a controllable range to prevent the generation of impurities) to obtain a first mixture, and add the concentrated ammonia water until the pH value of the first mixture is 9.8 - 10.2; (2) Wash the first mixture with quaternary deionized water multiple times and remove impurities to obtain a second mixture. Place the second mixture in a vacuum environment at 60°C and dry it for 12 hours. After drying, cool it to room temperature to obtain iron tetroxide (Fe3O4) nanoparticles. The vacuum degree of the vacuum environment is -0.08~-0.1Mpa.

[0010] Further, in the first step, the soil remediation agent is attapulgite with magnetic nanoparticles loaded on its surface.

[0011] Further, the magnetic nanoparticles are iron tetroxide (Fe3O4) nanoparticles.

[0012] Further, the particle size of the magnetic nanoparticles is 10 - 20nm.

[0013] Further, the mass ratio of the magnetic nanoparticles to attapulgite is 1:4 - 1:6.

[0014] Further, the slightly arsenic- and cadmium-polluted soil in the second step refers to the soil with a total arsenic content of 25 - 50 mg / kg and a total cadmium content of 0.6 - 1.5 mg / kg.

[0015] Further, the available arsenic (extracted by DTPA) in the slightly arsenic- and cadmium-polluted soil is 5-15 mg / kg, and the available cadmium (extracted by DTPA) is 0.2-0.5 mg / kg.

[0016] Further, in the second step, the base fertilizer is a fertilizer containing nitrogen (N), phosphorus (P), and potassium (K), and the mass ratio of nitrogen (N), phosphorus (P), and potassium (K) is: 15-18:15-18:6-10.

[0017] Further, the application rate of the base fertilizer in the second step is 35-45 kg / mu.

[0018] Further, in the second step, there are two ways to uniformly mix the base fertilizer and the soil remediation agent into the slightly arsenic- and cadmium-polluted soil. The first way is to plow the slightly arsenic- and cadmium-polluted soil first, evenly spread the base fertilizer and the soil remediation agent after plowing, and finally level the land; the second way is to evenly distribute the base fertilizer and the soil remediation agent to the slightly arsenic- and cadmium-polluted soil first, and then carry out plowing and land leveling operations in sequence. The first way has a better effect.

[0019] Further, when plowing the slightly arsenic- and cadmium-polluted soil, the plowing depth is 15-25 cm.

[0020] Further, in the third step, the low-accumulation metal wheat refers to wheat with an arsenic (As) content of ≤0.5 mg / kg and a cadmium (Cd) content of ≤0.1 mg / kg in the grains after maturity.

[0021] Further, in the fourth step, the composite foliar control agent includes mesoporous nano-zinc oxide, sodium selenite (Na2SeO3), plant endogenous hormones, L-ascorbic acid (VC), and ultrapure water. The proportion of mesoporous nano-zinc oxide in the composite foliar control agent is 5 g / L, the proportion of sodium selenite in the composite foliar control agent is 0.1 g / L, the proportion of plant endogenous hormones in the composite foliar control agent is 0.05 mg / L, and the proportion of L-ascorbic acid in the composite foliar control agent is 0.5 g / L. The particle size of the mesoporous nano-zinc oxide is 20-50 nm.

[0022] Further, there are several pore channels in the mesoporous nano-zinc oxide, and the pore diameter of the pore channels is 5-10 nanometers (nm).

[0023] Further, the plant endogenous hormone is brassinolide (BR).

[0024] Further, in the fourth step, the amount of the composite foliar control agent sprayed on the wheat leaves is 50 L / mu.

[0025] Further, in the fourth step, the compound foliar inhibitor is sprayed on the wheat leaves once during the booting stage and the filling stage of wheat. When spraying, it is preferably sprayed in the morning or evening when it is sunny and windless and there is no rainfall within 6 hours. If there is rainfall within 6 hours after spraying, 50% of the dose of the compound foliar inhibitor needs to be re-sprayed after the rainfall ends.

[0026] Beneficial effects: Compared with the prior art, the present invention has the following remarkable advantages: 1. The object of the present invention is soil with a total arsenic content of 25 - 50 mg / kg and a total cadmium content of 0.6 - 1.5 mg / kg. The arsenic and cadmium pollution degree of the soil is relatively light, so it is possible to balance land remediation and agricultural production; 2. In the plowing and soil preparation stage of the present invention, a base fertilizer and a soil remediation agent are uniformly mixed into the slightly arsenic- and cadmium-polluted soil. The soil remediation agent is attapulgite. As a typical layered chain silicate mineral, attapulgite has very distinct pore channel characteristics in terms of structure, and several pore channel characteristics have a certain adsorption effect on arsenic and cadmium; 3. The soil remediation agent used in the present invention is not ordinary attapulgite, but acid-activated attapulgite loaded with Fe3O4 nanoparticles on the surface. After attapulgite is acid-activated and loaded with Fe3O4 nanoparticles on the surface, the synchronous adsorption capacity for arsenic and cadmium is significantly improved, and arsenic and cadmium in the soil are passivated. The reason is that there are a large number of active sites (such as hydroxyl groups (-OH)) on the surface of Fe3O4 nanoparticles. These sites can form chemical bonds with arsenic or cadmium ions. At the same time, Fe3O4 nanoparticles have a high specific surface area and adsorb arsenic and cadmium ions through van der Waals forces and electrostatic forces. The iron ions (Fe²⁺ and Fe³⁺) on the surface of Fe3O4 nanoparticles can undergo ion exchange reactions with arsenic and cadmium ions. At pH 5 - 7, the surface of Fe3O4 nanoparticles is positively charged and is easy to adsorb negatively charged AsO3³⁻ / AsO4³⁻, thus completing the adsorption of arsenic and cadmium. In comparison, after Fe3O4 nanoparticles are loaded on the surface of attapulgite (i.e., after modification), more adsorption sites and synergistic effects can be provided compared with unmodified attapulgite, so the adsorption capacity for arsenic and cadmium can be significantly improved; 4. The present invention selects to plant low-accumulation metal wheat (such as Jimai 22) on slightly arsenic- and cadmium-polluted soil. The reasons are: 1. As a gramineous plant, wheat has a certain enrichment effect on arsenic and cadmium in the soil, so as to cooperate with the soil remediation agent to adsorb arsenic and cadmium; 2. However, the enrichment effect of low-accumulation metal wheat on arsenic and cadmium is not obvious, and the arsenic and cadmium contents in the grains after wheat maturity are within the safe range, thus ensuring agricultural production and food safety; 5. When planting low-accumulation metal wheat, a composite foliar control agent will be sprayed on the wheat leaves several times, especially at least once during the booting stage and filling stage of wheat. ① There are several pore channels with a pore diameter of 5 - 10 nm in the mesoporous nano-zinc oxide in the composite foliar control agent. Therefore, mesoporous nano-zinc oxide has a high loading efficiency and the ability to degrade arsenic and cadmium adsorbed on the leaves by photocatalytic performance. The principle of the ability to degrade arsenic and cadmium adsorbed on the leaves by photocatalytic performance is that mesoporous nano-zinc oxide generates electron-hole pairs (e⁻-h⁺) under light irradiation. The holes (h⁺) can directly oxidize As(III) and Cd(II) adsorbed on the leaf surface and convert them into low-toxic or stable forms (such as As(V), CdO). At the same time, the photo-generated electrons (e -) can reduce some heavy metal ions, thus synergistically reducing the ability of leaf organisms to effectively adsorb arsenic and cadmium; ② The selenium in sodium selenite can compete with arsenic for absorption sites, thereby organizing the transport of arsenic to the grains during wheat maturation as much as possible; ③ Brassinolide can activate the antioxidant system in wheat (such as SOD and POD enzymes) and alleviate oxidative stress; L-ascorbic acid can directly remove the reactive oxygen species (ROS) produced by heavy metal stress in wheat, enhance the stress resistance of wheat, and after spraying the composite foliar barrier agent, it can reduce the arsenic and cadmium content in the grains as much as possible to ensure food safety; 6. The surface of acid-activated attapulgite is loaded with Fe3O4 nanoparticles, which can easily separate the used soil remediation agent from the soil after a season of wheat matures for subsequent treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a flow chart of the present invention. DETAILED DESCRIPTION

[0028] The technical solution of the present invention is further described below in conjunction with the accompanying drawings.

[0029] Example

[0030] A piece of soil slightly contaminated by arsenic and cadmium, the soil type is clay loam, the pH is 5.8, the main pollutants in the soil are arsenic and cadmium, the total arsenic content is 25 mg / kg, the total cadmium content is 0.60 mg / kg. The effective arsenic (DTPA extraction) is 8.2 mg / kg, and the effective cadmium (DTPA extraction) is 0.25 mg / kg.

[0031] A method for repairing arsenic-cadmium contaminated soil and safely producing wheat, comprising the following steps: Step 1: Prepare soil remediation agent; Step 2: First, plow the soil to a depth of 20 cm, and leave it to rest for 5 days to stabilize the pH value. Part of the soil is planned as a blank area as a control group, and the remaining soil is a restoration area. Soil restoration agent and compound fertilizer are evenly spread into the restoration area at a rate of 200 kg / mu. The composition of the compound fertilizer is N-P2O5-K2O (the mass ratio of N:P:K is 16:16:8), and the amount of compound fertilizer used is 40kg / mu; Step 3: Sow the seeds of Maiji 22 in the soil slightly contaminated with arsenic and cadmium after the second step (including the blank area and the repaired area), with a sowing rate of 15 kg / mu and a row spacing of 20 cm. Apply urea at a rate of 20 kg / mu during the tillering stage of wheat, and carry out conventional irrigation and pest control; Step 4: During the wheat maturation process in the remediation area, at the booting stage of wheat (about 110 days after sowing) and the early filling stage (about 130 days after sowing), select a sunny and windless day, and spray the compound foliar control agent from 6:00 to 8:00 in the morning. The spraying amount is 50 L / mu. Use a knapsack sprayer to spray evenly. There should be no rainfall within 6 hours after spraying. If there is rainfall, make up the spray at 50% of the dose; Step 5: After the wheat is mature, harvest the wheat, and collect the soil in the remediation area and the blank area. Use DTPA to extract available arsenic and cadmium, and use ICP-MS to determine the arsenic and cadmium contents; after the wheat is mature, harvest it, separate the roots, stems and grains, dry and crush them, digest them with HNO3-H2O2, and use ICP-MS to determine the arsenic and cadmium contents.

[0032] The results are analyzed as follows: (1) The available arsenic and cadmium contents in the soil are shown in Table 1: Index Blank area Remediation area Reduction rate Available As (mg / kg) 8.2±0.5 3.9±0.3 58.2% Available Cd (mg / kg) 0.25±0.02 0.11±0.01 63.5% Table 1 (2) The arsenic and cadmium contents in the roots, stems, leaves and grains of wheat are determined by ICP-MS (unit: mg / kg), and the results are shown in Table 2: Part Remediation area (As) Remediation area (Cd) Blank area (As) Blank area (Cd) Root 12.5±1.2 1.8±0.15 15.3±1.5 2.4±0.20 Stem and leaf 2.1±0.18 0.45±0.04 3.6±0.25 0.92±0.08 Grain 0.48±0.03 0.10±0.01 0.95±0.06 0.32±0.02 Table 2 The arsenic and cadmium contents of the wheat grains obtained in the remediation area are reduced by 49.5% (As) and 68.8% (Cd) respectively compared with the arsenic and cadmium contents of the wheat grains obtained in the blank area, and both meet the GB 2762-2022 standard (As < 0.5 mg / kg, Cd < 0.1 mg / kg).

[0033] The steps for preparing the soil remediation agent are as follows: (A) Crush attapulgite to 100 mesh, put it into a 1.5 mol / L hydrochloric acid (HCl) solution and soak it for 3 hours after complete crushing. The volume ratio (unit: ml) of hydrochloric acid to the mass (unit: g) of attapulgite is 10:1. After soaking, take out the attapulgite, wash it until the pH value is neutral and then dry it to obtain acid-activated attapulgite; (B) Mix the obtained acid-activated attapulgite with the first deionized water. The mass ratio (unit: g) of acid-activated attapulgite to the volume (unit: ml) of the first deionized water is 10%, forming a uniform slurry. At the same time, mix iron oxide nanoparticles (Fe3O4) with the second deionized water. The mass ratio (unit: g) of iron oxide nanoparticles (Fe3O4) to the volume (unit: ml) of the second deionized water is 1:25 to obtain a magnetic solution, where the mass ratio of iron oxide nanoparticles (Fe3O4) to the mass of acid-activated attapulgite is 1:5; (C) The obtained magnetic solution was added dropwise to the slurry at a dropping rate of 1 mL / min. While adding the magnetic solution, the slurry was stirred at a speed of 500 rpm. After all the magnetic solution was added, a magnetic mixture was obtained. (D) The magnetic mixture was placed in a nitrogen atmosphere, and the nitrogen atmosphere was heated to 300 °C at a rate of 5 °C / min and calcined at 300 °C for 2 hours. After the calcination was completed, it was cooled to room temperature.

[0034] The magnetite (Fe3O4) nanoparticles can be either purchased as commercial products or prepared by oneself. If prepared by oneself, the steps are as follows: (1) Ferrous chloride (FeCl2) micro-particles and ferric chloride (FeCl3) micro-particles were mixed in a mass ratio of 1:3 and dissolved in tertiary deionized water. Then, concentrated ammonia water with a concentration of 26.5% was slowly added dropwise at a rate of 1.5 mL / min to obtain a first mixture. Concentrated ammonia water was added until the pH value of the first mixture reached 10. (2) The first mixture was washed three times with quaternary deionized water to remove impurities, obtaining a second mixture. The second mixture was placed in a vacuum environment at 60 °C and a vacuum degree of -0.3 Mpa and dried for 12 hours. After drying was completed, it was cooled to room temperature to obtain magnetite (Fe3O4) nanoparticles.

[0035] The composite foliar control agent includes mesoporous nano-zinc oxide, sodium selenite (Na2SeO3), brassinolide (BR), L-ascorbic acid (VC) and ultrapure water. The proportion of mesoporous nano-zinc oxide in the composite foliar control agent is 5 g / L, the proportion of sodium selenite in the composite foliar control agent is 0.1 g / L, the proportion of brassinolide (BR) in the composite foliar control agent is 0.05 mg / L, the proportion of L-ascorbic acid in the composite foliar control agent is 0.5 g / L, and the particle size of the mesoporous nano-zinc oxide is 20 - 50 nm. There are several pore channels in the mesoporous nano-zinc oxide, and the pore diameter of the pore channels is 5 - 10 nanometers (nm).

Claims

1. A method for repairing arsenic-cadmium contaminated soil and safely producing wheat, the steps are as follows: Step 1: Prepare soil remediation agent; Step 2: selecting soil slightly contaminated by arsenic and cadmium, and evenly mixing basal fertilizer and the soil remediation agent prepared in the first step into the soil slightly contaminated by arsenic and cadmium; Step 3: sowing seeds of low-metal-accumulating wheat in the soil slightly contaminated with arsenic and cadmium after the completion of step 2, and carrying out cultivation management, wherein the low-metal-accumulating wheat refers to wheat with an arsenic content of arsenic ≤ 0.5 mg / kg and a cadmium content of ≤ 0.1 mg / kg in the grain after maturity; Step 4: During the wheat maturation process, spray the compound foliar barrier agent on the wheat leaves several times; Step 5: Harvest the wheat when it is ripe.

2. A method for repairing arsenic-cadmium contaminated soil and safely producing wheat according to claim 1, characterized in that: The steps for preparing the soil remediation agent in the first step are as follows: (A) crushing attapulgite into 80-120 meshes, and soaking it in a 1.5 mol / L hydrochloric acid solution for 2-4 hours after it is completely crushed, wherein the ratio of the volume of the hydrochloric acid to the mass of the attapulgite is 10:1, taking out the attapulgite after the soaking, washing the attapulgite until the pH value is neutral, and then drying it to obtain acid-activated attapulgite; (B) mixing the obtained acid-activated attapulgite with a first deionized water, wherein the mass ratio of the acid-activated attapulgite to the volume of the first deionized water is 5% to 15%, to form a uniform slurry, and simultaneously mixing ferrosoferric oxide nanoparticles with a second deionized water, wherein the mass ratio of the ferrosoferric oxide nanoparticles to the volume of the second deionized water is 1:20 to 1:30, to obtain a magnetic solution, wherein the mass ratio of the ferrosoferric oxide nanoparticles to the mass of the acid-activated attapulgite is 1:4 to 1:6; (C) dropping the obtained magnetic solution into the slurry at a dropping speed of 0<v≤2 mL / min, stirring the slurry at a speed of 300 rpm≤r≤800 rpm while dropping the magnetic solution, and obtaining a magnetic mixture after all the magnetic solution has been dropped; (D) placing the magnetic mixture in a nitrogen atmosphere, heating the nitrogen atmosphere to 300° C. at a rate of 5° C. / min, calcining at 300° C. for 1.5 to 2.5 hours, and cooling to room temperature after calcination.

3. A method for repairing arsenic-cadmium contaminated soil and safely producing wheat according to claim 2, characterized in that: The preparation method of the ferroferric oxide nanoparticles is as follows: (1) mixing ferrous chloride particles and ferric chloride particles in a mass ratio of 1:3 and dissolving them in a third deionized water, slowly adding concentrated ammonia water with a concentration of 25% to 28% at a rate of 1 to 2 mL / min to obtain a first mixture, and adding the concentrated ammonia water until the pH value of the first mixture reaches 9.8 to 10.2; (2) Washing the first mixture multiple times with fourth deionized water to remove impurities to obtain a second mixture, drying the second mixture in a vacuum environment at 60° C. for 12 hours, and cooling the second mixture to room temperature to obtain ferrosoferric oxide nanoparticles.

4. The method of claim 1 for simultaneously repairing arsenic-cadmium contaminated soil and safely producing wheat, characterized in that: In the first step, the soil remediation agent is attapulgite with ferroferric oxide nanoparticles loaded on the surface, and the particle size of the magnetic nanoparticles is 10 to 20 nm.

5. The method of claim 1 for simultaneously repairing arsenic-cadmium contaminated soil and safely producing wheat, characterized in that: The soil slightly contaminated with arsenic and cadmium mentioned in the second step refers to soil with a total arsenic content of 25 to 50 mg / kg and a total cadmium content of 0.6 to 1.5 mg / kg.

6. The method of claim 1 for simultaneously repairing arsenic-cadmium contaminated soil and safely producing wheat, characterized in that: The base fertilizer in the second step is a fertilizer containing nitrogen, phosphorus and potassium, and the masses of the nitrogen, phosphorus and potassium are: 15-18:15-18:6-10.

7. The method of claim 1 for simultaneously repairing arsenic-cadmium contaminated soil and safely producing wheat, characterized in that: The composite foliar barrier agent in the fourth step includes mesoporous nano zinc oxide, sodium selenite, brassinolide, L-ascorbic acid and ultrapure water. The mesoporous nano zinc oxide accounts for 5 g / L of the composite foliar barrier agent, the sodium selenite accounts for 0.1 g / L of the composite foliar barrier agent, the brassinolide accounts for 0.05 mg / L of the composite foliar barrier agent, the L-ascorbic acid accounts for 0.5 g / L of the composite foliar barrier agent, and the particle size of the mesoporous nano zinc oxide is 20 to 50 nm.

8. The method of claim 1 for simultaneously repairing arsenic-cadmium contaminated soil and safely producing wheat, characterized in that: In the fourth step, the composite foliar barrier agent is sprayed once on the wheat leaves at the wheat heading stage and the wheat filling stage.

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