Soil heavy metal passivator as well as preparation method and application thereof

Abstract

The invention discloses a soil heavy metal passivator as well as a preparation method and application thereof. The preparation method comprises the following steps: preparing ferrihydrite pure powder; preparing pure ardealite powder; preparation of L-PR; and preparing the heavy metal passivator and the like. The soil conditioner has the remarkable effects that the pH value is adjusted to be close to neutral in the preparation process, so that the damage to the environment is reduced, the soil environment and the soil microbial community structure are improved, the self-repairing capability of soil is enhanced, and the ecological balance of the soil is favorably maintained; the cadmium and arsenic can be efficiently removed, the defects of an existing passivator in the aspect of treating the heavy metals are overcome, industrial waste residues are used as the passivator, the problems of resource waste and environmental pollution are solved, and the influence of the heavy metals on crop growth is reduced by improving the stress resistance of crops.

Description

Technical Field

[0001] The invention relates to the technical field of soil heavy metal passivation, and in particular to a soil heavy metal passivator and a preparation method and application thereof. Background Art

[0002] Soil heavy metal passivation technology has developed a variety of effective materials, which significantly reduce the bioavailability of heavy metals in the soil and improve the quality of crop growth. In particular, iron-based biochar and iron-based sulfur-rich materials are effective in reducing the absorption of cadmium and lead by rice. Global research is on the rise, with China and the United States being active, and the Chinese Academy of Sciences leading in this field.

[0003] Various types of passivators have been developed in the field of soil heavy metal passivators, mainly including inorganic ones (such as silicon, calcium, phosphorus substances and clay minerals), organic ones (such as organic fertilizers, straw and humic acid) and new materials (such as functional membrane materials, nanomaterials, mesoporous materials). However, these existing passivators have the following defects and deficiencies: 1. Excessive use of traditional passivators such as lime will lead to soil alkalinization, affecting the absorption of other nutrients, and cannot specifically reduce the effectiveness of specific heavy metals, such as arsenic and cadmium. The impact on soil microbial communities is unclear and may destroy the ecological balance of the soil. Moreover, the long-term effect is uncertain and frequent application is required to maintain its effect of passivating heavy metals.

[0004] 2. Excessive application of passivators such as phosphates may lead to accumulation of soil phosphorus and affect the absorption of other nutrients. They are sensitive to soil pH and their effects are limited by soil acidity and alkalinity. They work better in acidic soils but may not be as effective in alkaline soils. Furthermore, their application may cause phosphorus loss and lead to eutrophication of water bodies.

[0005] 3. The production cost of passivators such as biochar is relatively high, and they require specific biomass raw materials and pyrolysis conditions. Improper application may affect soil aeration and moisture retention, and their adsorption capacity for heavy metals is limited, especially for soils contaminated with high concentrations of heavy metals. The long-term effects and stability need further study. Summary of the invention

[0006] In view of the deficiencies in the prior art, the purpose of the present invention is to provide a soil heavy metal passivator and a preparation method and application thereof, aiming to address the limitations of existing soil heavy metal passivators in reducing the biological effectiveness of heavy metals in soil, improving crop growth quality and soil environmental safety.

[0007] To achieve the above object, the technical solution adopted by the present invention is as follows: In a first aspect, the present invention provides a method for preparing a soil heavy metal passivator, which comprises the following steps: Step 1, preparation of pure ferrihydrite powder; Step 2, preparation of pure phosphogypsum powder; Step 3, preparation of L-PR: Step 3.1, the pure phosphogypsum powder obtained in step 2 and red mud are mixed in a mass ratio of 1:4 to 1:2, and ultrapure water is added in a solid-liquid ratio of 1:20, stirred and dissolved, the mixed solution is centrifuged, the precipitate is dried, and ground to obtain a mixture powder; Step 3.2, take a certain amount of the mixture powder, add lanthanum salt solution at a solid-liquid ratio of 1:10 to 1:30, and stir to dissolve; Step 3.3, centrifuging the obtained solution and washing it with ethanol, drying the precipitate and then grinding it to obtain L-PR powder; Step 4, preparation of heavy metal passivator: according to the degree of soil pollution, the pure ferrihydrite powder obtained in step 1 and the L-PR powder obtained in step 3 are mixed in a mass ratio of 4:1 to 1:4.

[0008] Furthermore, the preparation process of the pure ferrihydrite powder in step 1 is as follows: Step 1.1, dissolve a certain amount of iron salt in ultrapure water; Step 1.2, adding alkaline solution to the iron salt solution, stirring the reaction, and adjusting the pH value to 7-8; Step 1.3, centrifuge the mixture at 4000 rpm for 5 min, pour off the supernatant, take out the precipitate, add ultrapure water and stir evenly, continue centrifugation, repeat the above process 6 to 8 times until the ferrihydrite is washed away; Step 1.4, put the washed precipitate into a dialysis bag, seal it, and dialyze it in ultrapure water, changing the water once a day. After dialysis for 7 days, measure the conductivity of the solution outside the dialysis bag. When the conductivity is not greater than the preset threshold, the dialysis is completed; Step 1.5, wash and centrifuge the dialyzed solution, take out the precipitate into a culture dish, freeze-dry for 48 hours, and then grind it to the first particle size to obtain pure ferrihydrite powder.

[0009] Furthermore, in step 1.1, the mass ratio of the iron salt to the ultrapure water is 4:50.

[0010] Furthermore, when the alkaline solution is added to the iron salt solution to adjust the pH value in step 1.2, the ferrihydrite solution is added dropwise.

[0011] Furthermore, in step 1.4, the preset threshold value of the conductivity is 10 μs / cm.

[0012] Furthermore, the preparation process of the pure phosphogypsum powder in step 2 is as follows: Step 2.1, take a certain amount of phosphogypsum and wash away soluble impurities with ultrapure water; Step 2.2, filtering the phosphogypsum solution, drying it in a vacuum drying oven at 80° C., and then grinding it to the second particle size to obtain the pure phosphogypsum powder.

[0013] Furthermore, the lanthanum salt solution in step 3 is LaCl3·7H2O solution.

[0014] Furthermore, the particle sizes of the mixture powder and the L-PR powder in step 3 are both no larger than 100 mesh.

[0015] In a second aspect, the present invention provides a soil heavy metal passivator prepared by the preparation method described in the first aspect.

[0016] In a third aspect, the present invention provides a use of the soil heavy metal passivator prepared in the first aspect in the treatment of heavy metal contaminated soil.

[0017] The remarkable effects of the present invention are: 1. During the preparation process, the pH value is adjusted to near neutral, which reduces damage to the environment, improves the soil environment and the structure of soil microbial communities, enhances the self-repairing ability of the soil, and helps maintain the ecological balance of the soil; the strong adsorption of ferrihydrite and L-PR materials is utilized to effectively reduce the effectiveness of heavy metals in the soil, which can specifically solve the problem of heavy metal pollution and improve soil quality and crop safety.

[0018] 2. It can improve the soil environment by adjusting the soil pH value and affecting the structure of rhizosphere microbial communities and root metabolites, reducing damage to the environment and helping to maintain the ecological balance of the soil.

[0019] 3. It can efficiently remove cadmium and arsenic, solving the shortcomings of existing passivators in dealing with these heavy metals. It uses industrial waste as a passivator to solve the problems of resource waste and environmental pollution, and reduces the impact of heavy metals on crop growth by improving the stress resistance of crops. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is a flow chart of the method of the present invention; Figure 2 This is a flow chart for the preparation of pure ferrihydrite powder. DETAILED DESCRIPTION

[0021] The specific implementation manner and working principle of the present invention are further described in detail below with reference to the accompanying drawings.

[0022] Embodiment 1: like Figure 1As shown, this embodiment provides a method for preparing a soil heavy metal passivator, and the specific steps are as follows: Step 1, preparation of pure ferrihydrite powder; Ferrihydrite (iron oxide): It is produced by the reaction of Fe(NO3)3·9H2O and KOH, with the chemical formula of 5Fe2O3·9H2O. It has a large specific surface area and surface positive charge, and has strong adsorption capacity for As(V).

[0023] In this embodiment, the preparation process of the pure ferrihydrite powder is as follows: Step 1.1, dissolve 40 g of Fe(NO3)3·9H2O in 500 mL of ultrapure water; Step 1.2, add 330 ml of 1 mol / L KOH solution to the Fe(NO3)3 solution, stir vigorously to react, and the last 20 ml should be added dropwise to adjust the pH value to 7-8; Step 1.3, centrifuge the mixture at 4000 rpm for 5 min, pour off the supernatant, take out the precipitate, add ultrapure water and stir evenly, continue centrifugation, repeat the above process 6 to 8 times until the ferrihydrite is washed away; Step 1.4, put the washed precipitate into a dialysis bag, seal it, and dialyze it in ultrapure water. Change the water once a day. After dialysis for 7 days, measure the conductivity of the solution outside the dialysis bag. When the conductivity is not greater than the preset threshold, the dialysis is completed. In this example, the preset threshold of the conductivity is 10 μs / cm. Step 1.5: Wash and centrifuge the dialyzed solution, take out the precipitate and put it into a culture dish, freeze-dry it for 48 hours, grind it to pass a 100-mesh sieve, and obtain pure ferrihydrite powder, which is then put into a ziplock bag for later use.

[0024] Step 2, preparation of pure phosphogypsum powder; Phosphogypsum: As an industrial byproduct, it contains ingredients such as CaSO4·2H2O, which can improve the resistance of crops to arsenic stress.

[0025] In this example, the preparation process of the pure phosphogypsum powder in step 2 is as follows: Step 2.1, take phosphogypsum from Kailin Group and wash away soluble impurities with ultrapure water; Step 2.2, filtering the phosphogypsum solution, drying it in a vacuum drying oven at 80°C, and then grinding it to 100 meshes to obtain the pure phosphogypsum powder.

[0026] Step 3, preparation of L-PR: Lanthanum (La) modified phosphogypsum red mud composite material (L-PR): has the characteristics of mesoporous materials and has high adsorption capacity for Cd(II) and As(V).

[0027] Step 3.1: Mix the pure phosphogypsum powder obtained in Step 2 and red mud at a mass ratio of 1:4, add ultrapure water at a solid-liquid ratio of 1:20, place it in a magnetic stirrer and stir thoroughly to dissolve. After centrifuging the mixed solution, take the precipitate, dry it, and grind it to 100 meshes to obtain a mixture powder; Step 3.2: Take a certain amount of the mixture powder in a beaker, add 0.1 mol / L LaCl3·7H2O solution at a solid-liquid ratio of 1:10, and stir for 5 h; Step 3.3: Centrifuge the obtained solution and wash it with ethanol. Take the precipitate, dry it at 80 °C and then grind it to obtain L-PR powder; Step 4: Preparation of heavy metal passivator: According to the degree of soil pollution, mix the pure ferrihydrite powder obtained in Step 1 and the L-PR powder obtained in Step 3 at a mass ratio of 4:1 to obtain the soil heavy metal passivator.

[0028] Example 2: The difference between this example and Example 1 is that: In Step 3.1, mix the pure phosphogypsum powder obtained in Step 2 and red mud at a mass ratio of 1:3.5; In Step 3.2, add 0.1 mol / L LaCl3·7H2O solution at a solid-liquid ratio of 1:15; In Step 4, mix the pure ferrihydrite powder obtained in Step 1 and the L-PR powder obtained in Step 3 at a mass ratio of 3:1 to prepare the soil heavy metal passivator.

[0029] Example 3: The difference between this example and Example 1 is that: In Step 3.1, mix the pure phosphogypsum powder obtained in Step 2 and red mud at a mass ratio of 1:3; In Step 3.2, add 0.1 mol / L LaCl3·7H2O solution at a solid-liquid ratio of 1:20; In Step 4, mix the pure ferrihydrite powder obtained in Step 1 and the L-PR powder obtained in Step 3 at a mass ratio of 1:1 to prepare the soil heavy metal passivator.

[0030] Example 4: The difference between this example and Example 1 is that: In Step 3.1, mix the pure phosphogypsum powder obtained in Step 2 and red mud at a mass ratio of 1:2.5; In Step 3.2, add 0.1 mol / L LaCl3·7H2O solution at a solid-liquid ratio of 1:25; In step 4, the pure ferrihydrite powder obtained in step 1 and the L-PR powder obtained in step 3 are mixed in a mass ratio of 2:3 to prepare the soil heavy metal passivator.

[0031] Embodiment 5: The difference between this embodiment and embodiment 1 is that: In step 3.1, the pure phosphogypsum powder obtained in step 2 and red mud are mixed in a mass ratio of 1:2; In step 3.2, add 0.1 mol / L LaCl3·7H2O solution at a solid-liquid ratio of 1:30; In step 4, the pure ferrihydrite powder obtained in step 1 and the L-PR powder obtained in step 3 are mixed in a mass ratio of 1:4 to prepare the soil heavy metal passivator.

[0032] The present invention also proposes an application of the soil heavy metal passivator for heavy metal passivation in soil, wherein the soil heavy metal passivator is selectively applied according to the degree of soil pollution. When the arsenic content in the soil exceeds the standard seriously, a soil heavy metal passivator with a higher proportion of ferrihydrite is selected for application; when the cadmium content in the soil exceeds the standard seriously, a soil heavy metal passivator with a higher proportion of L-PR is selected for application.

[0033] The application amount of soil heavy metal passivator is between 0.5% and 3% of the soil weight.

[0034] Application of passivator: Apply the prepared soil heavy metal passivator evenly to the surface of heavy metal contaminated soil, and adjust the application amount according to the heavy metal content in the soil and crop needs.

[0035] Irrigation and soil management: After applying the passivator, proper irrigation is carried out to ensure that the passivator is in full contact with the soil and improve the passivation effect. At the same time, soil pH and microbial community structure are monitored to evaluate the passivation effect.

[0036] Crop Planting and Management: Plant crops in the treated soil and carry out conventional field management, including fertilization, irrigation, and pest and disease control.

[0037] Finally, the soil heavy metal passivator prepared in Example 1 of the present invention was applied to farmland soil around a high-arsenic coal mine in Guizhou, and the results showed that the arsenic content in the aboveground part of the crop was reduced by 25.95%, and the dry weight of the crop increased by 433.33%. The soil heavy metal passivator prepared in Example 5 of the present invention was applied to a cadmium-contaminated rice field in Hunan, and the results showed that the effective Cd content in the soil was reduced by 82.04%, and the Cd content in rice was reduced by 71.90%.

[0038] In summary, the advantages of the present invention are as follows: Neutral pH adjustment: The present invention precisely controls the pH value during the preparation process to a neutral range (pH 7-8), thereby avoiding the soil alkalinization problem caused by excessive use of traditional alkaline passivators such as lime. This neutral pH adjustment helps to protect the soil structure and reduce damage to the soil microbial community, thereby maintaining the ecological balance of the soil.

[0039] Application of strong adsorption materials: Utilize the strong adsorption of ferrihydrite and L-PR (lanthanum modified phosphogypsum red mud composite material) to specifically reduce the effectiveness of heavy metals such as arsenic and cadmium in the soil. This strong adsorption material can effectively reduce the absorption of heavy metals by crops and improve the safety and yield of crops.

[0040] Resource Utilization of Industrial Waste Residues: Using phosphogypsum, an industrial byproduct, as a raw material for passivation agents realizes the resource utilization of industrial waste residues. This method not only reduces the environmental burden of industrial waste residues, but also provides a cost-effective soil remediation material.

[0041] Improvement of microbial community structure: The present invention enhances the self-repairing ability of the soil by changing the microbial community structure of the rhizosphere soil. The improved microbial community structure helps to improve soil quality and enhance the resistance of crops to heavy metal stress.

[0042] Highly efficient removal of heavy metals: L-PR has extremely high removal efficiencies for Cd(II) and As(V), exceeding 97.57% and 99.00% respectively. This high removal capacity significantly reduces the heavy metal content in soil and crops, improving crop safety.

[0043] Environmental friendliness: The passivating agent of the present invention has little impact on the environment during its preparation process, and the final product is safe and non-toxic, with no excessive heavy metals. This environmental friendliness ensures that the use of the passivating agent will not cause secondary pollution to the soil and the environment.

[0044] Improvement of soil physical and chemical properties: After L-PR treatment, soil pH and cation exchange capacity (CEC) increased, which were negatively correlated with the available Cd and As contents. This improvement helps reduce the bioavailability of heavy metals and their risks to crops and the environment.

[0045] Interaction between root metabolites and microbial communities: After L-PR treatment, the correlation between rice root exudates and rhizosphere microorganisms was high, which may affect the rhizosphere soil environment by positively or negatively regulating the microbial community. This interaction helps to further improve the soil environment and enhance the growth quality and stress resistance of crops.

[0046] The technical solution provided by the present invention is described in detail above. Specific examples are used herein to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea. It should be pointed out that for ordinary technicians in this technical field, without departing from the principle of the present invention, several improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a soil heavy metal passivator, characterized in that: The steps include: Step 1, preparation of pure ferrihydrite powder; Step 2, preparation of pure phosphogypsum powder; Step 3, preparation of L-PR: Step 3.1, the pure phosphogypsum powder obtained in step 2 and red mud are mixed in a mass ratio of 1:4 to 1:2, and ultrapure water is added in a solid-liquid ratio of 1:20, stirred and dissolved, the mixed solution is centrifuged, the precipitate is dried, and ground to obtain a mixture powder; Step 3.2, take a certain amount of the mixture powder, add lanthanum salt solution at a solid-liquid ratio of 1:10 to 1:30, and stir to dissolve; Step 3.3, centrifuging the obtained solution and washing it with ethanol, drying the precipitate and then grinding it to obtain L-PR powder; Step 4, preparation of heavy metal passivator: according to the degree of soil pollution, the pure ferrihydrite powder obtained in step 1 and the L-PR powder obtained in step 3 are mixed in a mass ratio of 4:1 to 1:

4.

2. The soil heavy metal passivator according to claim 1, characterized in that: The preparation process of the pure ferrihydrite powder in step 1 is as follows: Step 1.1, dissolve a certain amount of iron salt in ultrapure water; Step 1.2, adding alkaline solution to the iron salt solution, stirring the reaction, and adjusting the pH value to 7-8; Step 1.3, centrifuge the mixture at 4000 rpm for 5 min, pour off the supernatant, take out the precipitate, add ultrapure water and stir evenly, continue centrifugation, repeat the above process 6 to 8 times until the ferrihydrite is washed away; Step 1.4, put the washed precipitate into a dialysis bag, seal it, and dialyze it in ultrapure water, changing the water once a day. After dialysis for 7 days, measure the conductivity of the solution outside the dialysis bag. When the conductivity is not greater than the preset threshold, the dialysis is completed; Step 1.5, wash and centrifuge the dialyzed solution, take out the precipitate and put it into a culture dish, freeze-dry it for 48 hours, and then grind it into the first particle size to obtain pure ferrihydrite powder.

3. The soil heavy metal passivator according to claim 2, characterized in that: The mass ratio of iron salt to ultrapure water in step 1.1 is 4:

50.

4. The soil heavy metal passivator according to claim 2, characterized in that: When the alkaline solution is added to the iron salt solution to adjust the pH value in step 1.2, the ferrihydrite solution is added dropwise.

5. The soil heavy metal passivator according to claim 2, characterized in that: In step 1.4, the preset threshold value of the conductivity is 10 μs / cm.

6. The soil heavy metal passivator according to claim 1, characterized in that: The preparation process of the pure phosphogypsum powder in step 2 is as follows: Step 2.1, take a certain amount of phosphogypsum and wash away soluble impurities with ultrapure water; Step 2.2, filtering the phosphogypsum solution, drying it in a vacuum drying oven at 80° C., and then grinding it to the second particle size to obtain the pure phosphogypsum powder.

7. The soil heavy metal passivator according to claim 1, characterized in that: The lanthanum salt solution in step 3 adopts LaCl3·7H2O solution.

8. The soil heavy metal passivator according to claim 1, characterized in that: The particle sizes of the mixture powder and the L-PR powder in step 3 are both no larger than 100 meshes.

9. A soil heavy metal passivator prepared by the preparation method according to any one of claims 1 to 8.

10. Use of a soil heavy metal passivator prepared by the preparation method according to any one of claims 1 to 8 in the treatment of heavy metal contaminated soil.

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