Preparation method and application of soil additive capable of simultaneously reducing accumulation of heavy metals and micro-plastics in vegetables

Abstract

The invention discloses a preparation method and application of a soil additive capable of simultaneously reducing accumulation of heavy metals and micro-plastics in vegetables. The preparation method comprises preparation of modified biochar and preparation of the soil additive containing the modified biochar. According to the efficient modified charcoal obtained by the preparation method, a soil additive capable of reducing the content of heavy metals and micro-plastics in vegetables at the same time is compounded. The additive has the characteristics of being direct, efficient and environment-friendly. Meanwhile, the soil additive provided by the invention has an effect of improving the biomass of plants and can promote the growth of the plants.

Description

Technical Field

[0001] The present invention belongs to the technical field of soil additives, and particularly relates to a preparation method and application of a soil additive for simultaneously reducing the accumulation of heavy metals and microplastics in vegetables. Background Art

[0002] Soil heavy metal pollution not only affects the physical, chemical properties and biological activities of the soil, but also affects the physiological characteristics of plants such as plant height, main root length, and leaf area. It can also accumulate in the human body at harmful concentrations through the food chain, seriously endangering human health.

[0003] Vegetables are essential foods on the table. Micro-nano plastics can not only directly enter vegetable organs or tissues, affecting plant physiology, but also interact with pollutants such as heavy metals, producing combined toxicity, and ultimately threatening human health through food chains, food webs, etc.

[0004] The patent "A Heavy Metal Polluted Soil Remediation Conditioner and Its Application" (Publication No.: CN106978185A) provides a soil remediation conditioner containing sulfur-modified biochar, attapulgite, zeolite, iron powder and lime substances, which has a strong adsorption capacity for heavy metals and has a significant stabilization effect on heavy metals in heavy metal composite polluted soil, reducing the activity and bioavailability of the corresponding heavy metals.

[0005] The prior art provides the application of modified biochar in heavy metal adsorption, but there is little research on whether it can play a good role in reducing nano plastics. Therefore, it is crucial to prepare an efficient additive that can simultaneously reduce the accumulation of heavy metals and microplastics in vegetables to ensure human safety. Summary of the Invention

[0006] In view of the deficiencies of the prior art, the present invention provides a preparation method and application of a soil additive for simultaneously reducing the accumulation of heavy metals and microplastics in vegetables.

[0007] In view of the above deficiencies, the present invention provides highly efficient modified biochar, verifies it under various pollution conditions, and then uses the modified biochar as the main material to compound a soil additive that can simultaneously reduce the content of heavy metals and microplastics in vegetables. This soil additive has the characteristics of being directly efficient and environmentally friendly.

[0008] In the first aspect of the present invention, it is intended to provide a preparation method of a soil additive for simultaneously reducing the accumulation of heavy metals and microplastics in vegetables, including the preparation of modified biochar and the preparation of a soil additive containing modified biochar; wherein, the preparation of modified biochar includes the following steps:

[0009] Step S1, Pyrolysis: Take plant straws and perform staged pyrolysis. The first pyrolysis temperature is 400 - 600 °C, and then the pyrolysis temperature is 600 - 800 °C;

[0010] Preferably, the first pyrolysis time is 1 - 2 h; the second pyrolysis time is 1 - 2 h;

[0011] The plant straws are selected from wheat, rice, and corn straws.

[0012] In the embodiment of the present invention, fill a crucible with crushed and ground rice straws, cover the lid, and perform oxygen-deficient carbonization in a programmable electric furnace. Set the pyrolysis temperature to 500 °C and pyrolyze for 1 h; then the pyrolysis temperature is 700 °C and pyrolyze for 1 h; when the programmable electric furnace cools to room temperature, grind the black solid through a 0.15 mm sieve to obtain rice straw biochar.

[0013] Step S2, Alkali modification: Take the biochar obtained in Step S1 and immerse it in an alkali solution, then heat and stir;

[0014] In the embodiment of the present invention, use a magnetic stirrer, and control the temperature of the magnetic stirrer at 60 ± 5 °C, and the stirring speed is 600 - 800 rpm;

[0015] In the embodiment of the present invention, the alkali solution is selected from KOH, NaOH, Ca(OH) 2 solution, and the concentration is 1 M - 4 M.

[0016] Step S3, Acid modification: Take the biochar obtained in Step S2, wash it until the pH is stable, and then immerse it in an acid solution and stir;

[0017] In the embodiment of the present invention, use a magnetic stirrer to control stirring under room temperature conditions, and the stirring speed is 600 - 800 rpm;

[0018] In the embodiment of the present invention, the acid solution uses a weak acid solution, including citric acid or acetic acid; acetic acid is a 10% - 40% solution.

[0019] Step S4, Secondary alkali modification: Take the biochar obtained in Step S3, wash it until the pH is stable, and then immerse it in an alkali solution for secondary alkali modification.

[0020] Step S5, Take the biochar obtained in Step S4, wash it until the pH is stable, and then dry it to obtain the alkali-acid-alkali combined modified biochar.

[0021] Furthermore, the preparation of the soil additive containing the modified biochar includes the following method: After quicklime and zeolite are crushed, ground, and sieved, combine the alkali-acid-alkali combined modified biochar: quicklime: zeolite in a mass ratio of 6 - 8:1 - 2:1 - 2, and fully mix to obtain the soil additive.

[0022] Further, quicklime and zeolite are crushed, ground, and sieved through a 0.15 mm sieve.

[0023] Further, the mass ratio of alkali-acid-alkali combined modified biochar: quicklime: zeolite is 8:1:1.

[0024] The second aspect of the present invention lies in providing a soil additive prepared by the said preparation method.

[0025] The third aspect of the present invention lies in providing the application of the said soil additive in reducing the accumulation of heavy metals and microplastics in vegetables.

[0026] The said vegetables are leafy vegetables, including lettuce, rape, Chinese cabbage, and spinach;

[0027] The said heavy metals are cationic heavy metals, including Cd, Pb, Cu, and Ni.

[0028] Compared with the prior art, the beneficial effects of the present invention are:

[0029] (1) Aiming at the current situation of the lack of soil additives that can efficiently reduce heavy metals and micro / nano plastics in vegetables, the present invention provides a highly efficient modified biochar. It is verified and compared under various pollution conditions and confirmed that this component is superior to other biochar modification strategies. Then, using this modified biochar as the main material, a soil additive that can simultaneously reduce the heavy metal and microplastic contents in vegetables is compounded; this additive has the characteristics of being direct, efficient, and environmentally friendly.

[0030] (2) The modification of biochar in the present invention adopts the KOH-HAc-KOH composite modification method, which provides Cd binding sites and enables the formation of complexes, thereby improving the specific adsorption of Cd; in addition, in the product obtained by alkali-acid-alkali composite modification, the stretching vibrations of oxygen-containing functional groups such as O-H and C=O are beneficial to the adsorption of pollutants such as PS-NPs. 2+ Furthermore, in the product obtained by alkali-acid-alkali composite modification, the stretching vibrations of oxygen-containing functional groups such as O-H and C=O are conducive to the adsorption of pollutants such as PS-NPs.

[0031] (3) It has been proved by experiments that the soil additive provided by the present invention has an effect of improving the biomass of plants and can promote plant growth. Description of the Drawings

[0032] The specification drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention.

[0033] Figure 1 It is the content of Cd and PS-NPs in the above-ground part of lettuce in Test Example 1; among them, (a) is the content of Cd in the above-ground part, and (b) is the content of PS-NPs in the above-ground part.

[0034] Figure 2 For the contents of Cd and PS-NPs in the roots of lettuce in Test Example 1; among them, (a) is the Cd content in the roots, and (b) is the PS-NPs content in the roots.

[0035] Figure 3 For the contents of Cd and PS-NPs in the above-ground parts of lettuce in Test Example 2; among them, (a) is the Cd content in the above-ground parts, and (b) is the PS-NPs content in the above-ground parts.

[0036] Figure 4 For the contents of Cd and PS-NPs in the roots of lettuce in Test Example 2; among them, (a) is the Cd content in the roots, and (b) is the PS-NPs content in the roots.

[0037] Figure 5 For the contents of Cd and PS-NPs in the above-ground parts of lettuce in Test Example 3; among them, (a) is the Cd content in the above-ground parts, and (b) is the PS-NPs content in the above-ground parts.

[0038] Figure 6 For the contents of Cd and PS-NPs in the roots of lettuce in Test Example 3; among them, (a) is the Cd content in the roots, and (b) is the PS-NPs content in the roots.

[0039] Figure 7 For the biomass of the roots and above-ground parts of lettuce in Test Example 4; among them, (a) is the root biomass, and (b) is the above-ground biomass.

[0040] Figure 8 For the contents of Cd and PS-NPs in the above-ground parts of lettuce in Comparative Example 2; among them, (a) is the Cd content in the above-ground parts, and (b) is the PS-NPs content in the above-ground parts.

[0041] Figure 9 For the contents of Cd and PS-NPs in the roots of lettuce in Comparative Example 2; among them, (a) is the Cd content in the roots, and (b) is the PS-NPs content in the roots. Detailed implementation manners

[0042] It should be noted that the following detailed descriptions are all exemplary and are intended to provide further explanations of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs.

[0043] In the embodiments of the present invention, the preparation of the soil additive is described by taking rice straw as an example, and crop straws such as wheat and corn can also be used for the preparation of the soil additive.

[0044] Example 1, Preparation method of soil additive

[0045] Preparation and modification of biochar: Fill a crucible with crushed and ground rice straw, cover the lid, and carbonize it under anoxic conditions in a programmable electric furnace. Set the pyrolysis temperature to 500 °C and pyrolyze for 1 h; then set the pyrolysis temperature to 700 °C and pyrolyze for 1 h. When the programmable electric furnace cools to room temperature, grind the black solid and pass it through a 0.15 mm sieve to obtain rice straw biochar. Take 20 g of the ground rice straw biochar, (1) immerse it in 100 mL of a potassium hydroxide solution with a concentration of 2 M, control the temperature at 60 °C with a magnetic stirrer, the stirring speed is 600 - 800 rpm, and the stirring time is 1 h; (2) wash the biochar with deionized water until the pH is stable, then immerse the biochar in 100 mL of acetic acid with a volume fraction of 20%, control the stirring time at room temperature with a magnetic stirrer for 2 h, and the stirring speed is 600 - 800 rpm; (3) wash the biochar with deionized water until the pH is stable, repeat step (1), and then immerse it in 100 mL of a potassium hydroxide solution with a concentration of 2 M, control the temperature at 60 °C with a magnetic stirrer, the stirring speed is 600 - 800 rpm, and the stirring time is 1 h. Wash the biochar with deionized water until the pH is stable, and dry it at 90 °C to obtain the alkali-acid-alkali combined modified biochar.

[0046] Preparation of soil additive: Quicklime and zeolite are crushed and ground, and then ground through a 0.15 mm sieve. Combine the modified biochar: quicklime: zeolite in a mass ratio of 8:1:1, and fully mix to obtain this soil additive.

[0047] In other embodiments, the first pyrolysis temperature is 400 - 600 °C (1 - 2 h), and then the pyrolysis temperature is 600 - 800 °C (1 - 2 h).

[0048] The present invention provides a method for KOH-HAc-KOH composite modification of biochar. In other embodiments, alkalis such as NaOH and Ca(OH) 2 can be used in steps (1) and (3); weak acids such as citric acid can be used in step (2).

[0049] In steps (1) and (3), the concentration of the KOH solution is 1 M - 4 M, in step (2), HAc is a 10% - 40% solution, and the modification time is 1 - 4 h.

[0050] As a feasible method, in the preparation of the soil additive, the modified biochar: quicklime: zeolite can be mixed in a mass ratio of 6 - 8:1 - 2:1 - 2.

[0051] Quantification of nanoplastics: The patent application "Method for Analyzing the Enrichment Amount and Distribution of Nanoplastics in Marine Organisms in the Laboratory" (Publication No.: CN117169323A) provides a method for constructing a europium element-nanoplastic standard curve to determine Eu; in this example, fluorescent nanoplastics microspheres (100 nm) doped with europium chelate Eu-β-diketonate (PS-Eu) are used, and the ion component release amount during exposure to the simulated solution is <0.2%, with good stability. Method for quantifying the content of nanoplastics in plants based on the self-built europium labeling technology: By measuring the Eu content in the PS-Eu nanoplastics microspheres, the calibration curve y = 0.323x between the nanoplastics mass and the Eu mass is obtained, and the R 2 value is 0.9979, indicating that by measuring the Eu content in the unknown sample, the content of PS-Eu can be determined based on this relationship. The actually measured Eu addition amount by ICP-MS is 0.31%, and compared with the designed addition amount of 0.32%, the difference is within the acceptable range, and the materials and methods have been verified to meet the test requirements.

[0052] Test Example 1: Reduction effect of ALCL (Alkaline-Acid-Alkaline) modified biochar on Cd and PS-NPs in lettuce (I)

[0053] Using the common lettuce on the table as the test plant and the common heavy metals and microplastics in farmland soil, Cd and polystyrene nanoplastics (PS-NPs), as pollutants, to study the reduction effect of ALAL modified biochar on the contents of Cd and PS-NPs in lettuce. When the soil Cd content is 3 mg / kg, 6 tests with different treatments are set up, and the specific test design is shown in Table 1.

[0054] Table 1 Test design (Cd: 3 mg / kg)

[0055]

[0056]

[0057] As Figure 1As shown in (a) and (b), in the edible part of lettuce that is most concerned about - the above-ground part, the Cd content and PS-NPs content in this part both decreased significantly with the increase in the addition amount of modified biochar (P<0.05). At the pollution level of Cd at 3 mg / kg and PS-NPs at 0.01% (w / w) (T1-T3), when the addition amount of modified biochar was 5%, the Cd content and PS-NPs content in the above-ground part decreased by 71.57% and 72.32% respectively. Similarly, at the pollution level of Cd at 3 mg / kg and PS-NPs at 0.1% (w / w) (T4-T6), when the addition amount of modified biochar was 5%, the Cd content and PS-NPs content in the above-ground part decreased by 78.84% and 55.81% respectively.

[0058] As Figure 2 As shown in (a) and (b), similar to the above-ground part of lettuce, the Cd content and PS-NPs content in the lettuce roots also decreased significantly with the increase in the addition amount of modified biochar (P<0.05). At the pollution level of Cd at 3 mg / kg and PS-NPs at 0.01% (w / w) (T1-T3), when the addition amount of modified biochar was 5%, the Cd content and PS-NPs content in the roots decreased by 77.32% and 76.88% respectively. Similarly, at the pollution level of Cd at 3 mg / kg and PS-NPs at 0.1% (w / w) (T4-T6), when the addition amount of modified biochar was 5%, the Cd content and PS-NPs content in the roots decreased by 77.38% and 86.45% respectively.

[0059] Experimental Example 2: Reduction effect of ALCL-modified biochar on Cd and PS-NPs in lettuce (Part 2)

[0060] Similarly, using the common lettuce on the dining table as the test plant and the common heavy metals and microplastics Cd and PS-NPs in farmland soil as pollutants, the reduction effect of ALCL-modified biochar on the Cd and PS-NPs content in lettuce was studied. When the soil Cd content was 6 mg / kg, 6 experiments with different treatments were set up, and the specific experimental design is shown in Table 2.

[0061] Table 2 Experimental design (Cd: 6 mg / kg)

[0062] Treatment Heavy metal content Microplastic content Modified biochar addition amount T7 6 mg / kg 0.01% PS-NPs 0 T8 6 mg / kg 0.01% PS-NPs 1％ T9 6 mg / kg 0.01% PS-NPs 5％ T10 6 mg / kg 0.1% PS-NPs 0 T11 6 mg / kg 0.1% PS-NPs 1％ T12 6 mg / kg 0.1% PS-NPs 5％

[0063] As Figure 3As shown in (a) and (b), in the above-ground part of lettuce that was the focus of attention, the Cd content and PS-NPs content in this part both decreased significantly with the increase in the addition amount of modified biochar (P<0.05). At the pollution level of Cd at 6 mg / kg and PS-NPs at 0.01% (w / w) (T7-T9), when the addition amount of modified biochar was 5%, compared with the T7 treatment, the Cd content and PS-NPs content in the above-ground part decreased by 85.79% and 46.29% respectively. Similarly, at the pollution level of Cd at 6 mg / kg and PS-NPs at 0.1% (w / w) (T10-T12), when the addition amount of modified biochar was 5%, compared with the T10 treatment, the Cd content and PS-NPs content in the above-ground part decreased by 82.73% and 43.95% respectively.

[0064] As Figure 4 As shown in (a) and (b), similar to the above-ground part of lettuce, the Cd content and PS-NPs content in the lettuce roots also decreased significantly with the increase in the addition amount of modified biochar (P<0.05). At the pollution level of Cd at 6 mg / kg and PS-NPs at 0.01% (w / w) (T7-T9), when the addition amount of modified biochar was 5%, compared with the T7 treatment, the Cd content and PS-NPs content in the roots decreased by 88.53% and 74.70% respectively. Similarly, at the pollution level of Cd at 6 mg / kg and PS-NPs at 0.1% (w / w) (T10-T12), when the addition amount of modified biochar was 5%, compared with the T10 treatment, the Cd content and PS-NPs content in the roots decreased by 79.39% and 81.99% respectively.

[0065] In summary, for the Cd and PS-NPs combined contaminated soils with 4 different pollution levels, when the addition amount of ALCL modified biochar was 5%, it was expected to reduce the Cd content in the edible above-ground part of lettuce by 70%-90% and the PS-NPs content by 40%-80%.

[0066] Experimental Example 3: Reduction effect of this soil additive on Cd and PS-NPs in lettuce

[0067] Select the most severe situation among the above 4 pollution levels, that is, the pollution level of Cd at 6 mg / kg and PS-NPs at 0.1% (w / w). Compare the effects of 3 different soil additives on the Cd and PS-NPs contents in lettuce when the addition amount is 5%. The specific experimental design is shown in Table 3 below.

[0068] Table 3 Experimental design of soil additives

[0069]

[0070] As Figure 5As shown in (a) and (b), compared with the effect of single modified biochar (C1), under the action of two composite additives C2 and C3, ① the Cd content in the above-ground part of lettuce decreased significantly by 14.00% and 8.01% respectively (P<0.05), and there was no significant difference between the two composite additives; ② the PS-NPs content in the above-ground part of lettuce increased by 18.23% and 3.75% respectively, and the increase in PS-NPs under the action of the C2 composite additive reached a significant level (P<0.05). Compared with C1, C2 is biochar + lime, which can not only reduce the Cd content but also significantly increase the plant PS-NPs content, which may be related to the reduction of the addition amount of modified biochar; compared with single biochar (C1), the treatment of biochar + lime + zeolite (C3) can reduce the plant Cd content and has no significant adverse effect on the enrichment of PS-NPs, so this composite method is relatively successful. Compared with the treatment without additives (T10 treatment), the Cd content and PS-NPs content in the above-ground part of lettuce decreased by 84.62% and 39.37% respectively.

[0071] As Figure 6 As shown in (a) and (b), compared with the effect of single modified biochar (C1), under the action of two composite additives C2 and C3, ① the Cd content in the roots of lettuce decreased significantly by 19.14% and 14.34% respectively (P<0.05), and there was no significant difference between the two composite additives; ② the PS-NPs content in the roots of lettuce increased by 15.56% and 5.58% respectively, and the increase in PS-NPs under the action of the C2 composite additive reached a significant level (P<0.05). Compared with the treatment without additives (T10 treatment), the Cd content and PS-NPs content in the roots of lettuce decreased by 80.34% and 80.43% respectively.

[0072] Similarly, the modified biochar provided by the present invention also has the effect of reducing the accumulation of heavy metals and microplastics in other leafy vegetables, including rape, Chinese cabbage and spinach. The heavy metals include cationic heavy metals such as Cd, Pb, Cu and Ni.

[0073] Experimental example 4, the soil additive also has a significant promoting effect on plant growth

[0074] Adopting the experimental design conditions of Experimental example 3, the effect on plant growth was investigated, and it was found that in addition to reducing the pollutant content in the roots and above-ground parts of lettuce, this soil additive also has a significant promoting effect on plant growth. The results are as Figure 7As shown in (a) and (b), compared with the single biochar treatment (C1), the C3 soil additive (modified biochar: lime: zeolite = 8:1:1) can significantly increase the biomass of lettuce roots and shoots (P<0.05), with increases of 55.56% and 19.84% respectively. Compared with the treatment without additives (T10 treatment), the biomass of lettuce roots and shoots increased by 96% and 67.73% respectively under C3 treatment.

[0075] In summary, the high-efficiency soil additive composed of modified biochar as the main body, combined with lime and zeolite in a ratio of 8:1:1, has an efficient effect on reducing the Cd content and PS-NPs content in the edible parts above the ground and roots of lettuce. In addition, under the action of this additive, the biomass of lettuce can be significantly increased, which has a strong promoting effect on plant growth. It is also worth mentioning that the raw materials of this soil additive are widely sourced, and compared with other commonly used chemical reagents, this additive has prominent environmental protection advantages.

[0076] Comparative Example 1: Selection of highly efficient modified biochar based on FTIR

[0077] For the prepared modified biochar, the following modifications were carried out respectively: (1) 1M acetic acid modification; (2) 2M acetic acid modification; (3) 1M KOH modification; (4) 2M KOH modification; (5) KOH-HAc (2M) composite modification (i.e., ALC composite modification); (6) HAc-KOH (2M) composite modification (i.e., ACL composite modification); (7) KOH-HAc-KOH (2M) composite modification (i.e., ALCL composite modification). The chemical structures and compositions of the seven modified biochars and the unmodified biochar were analyzed by Fourier transform infrared absorption spectrometer (FTIR). Equations (1) and (2) were introduced, and the r i value and R i value were used to compare the effects of different modification treatments on the peak area and peak height of biochar:

[0078] r i = A i / A 0 ......(1)

[0079] R i = H i / H 0 ......(2)

[0080] In the equations, r i and R i respectively represent the ratios of the peak area and peak height of the modified biochar i to those of the unmodified biochar; A i and H i respectively represent the peak area and peak height of the modified biochar i; A 0 and H0 They respectively represent the peak area and peak height of unmodified biochar. The specific results are shown in Table 4:

[0081] Table 4 Peak Heights and Peak Areas of Characteristic Peaks of Different Modified Biochars

[0082]

[0083] Note: Higher than 1 indicates better than before modification, and lower than 1 indicates lower than before modification.

[0084] In this study, the -OH groups around 3440 cm -1 and the C=C groups around 1635 cm -1 were mainly concerned. The test results showed that the r -1 value and R i value of 2M KOH-modified biochar at 3440 cm i (-OH) were the highest, being 1.69 and 1.57 respectively; at 1635 cm -1 (C=C), the r i value and R i value were also the highest, being 1.80 and 1.80 respectively (Table 4). In addition, the r -1 value and R -1 value of the biochar modified by ALCL complex at 3440 cm i (-OH) and 1635 cm i (C=C) were also relatively high. Analyzing its principle: The complexation of Cd on the biochar surface is closely related to functional groups such as -OH, -C=O / -C=C. The above functional groups provide binding sites for Cd, enabling it to form complexes, thereby enhancing the specific adsorption of Cd 2+ . In addition, the stretching vibrations of oxygen-containing functional groups such as O-H and C=O are conducive to the adsorption of pollutants such as PS-NPs.

[0085] Comparative Example 2:

[0086] The contents of Cd and PS-NPs in the soil were set to be 6 mg / kg -1 and 0.1% (w / w) respectively. Three modified biochars with relatively large peak areas and peak heights in Comparative Example 1 (i.e., 2M KOH-modified biochar, ALC complex-modified biochar, and ALCL complex-modified biochar) were selected for pot experiments to obtain the modified biochar with the best effect.

[0087] As Figure 8As shown in (a) and (b), (1) when the soil biochar addition amount is 1%, there is no significant difference in the Cd contents between the roots and shoots of lettuce under the action of the three biochars (P<0.05); (2) when the soil biochar addition amount is 5%, the Cd contents in the roots and shoots of lettuce under the action of the ALC composite modified biochar are significantly higher than those under the KOH modification and the ALCL composite modification. The reasons may be related to the following aspects: i) Compared with the KOH modified and ALCL composite modified biochars, the pH value of the soil under the action of the ALC composite modified biochar is lower, resulting in higher bioavailability of Cd in the soil. Therefore, the absorption and transport of Cd by lettuce are stronger; ii) As shown in Table 4, the types and vibration peak intensities of the key oxygen-containing functional groups lead to lower ability to act on soil Cd compared with the KOH modification and the ALCL composite modification. Therefore, in terms of Cd content, the effects of the KOH modified and ALCL composite modified biochars are both good.

[0088] As Figure 9 As shown in (a) and (b), (1) when the soil biochar addition amount is 1%, the difference in the PS-NPs contents between the roots and shoots of lettuce under the action of the three biochars is not significant, and only the root PS-NPs content under the action of the KOH modified biochar is higher; (2) when the soil biochar addition amount is 5%, the ACLC composite modified biochar shows significant advantages. Under its action, the PS-NPs contents in both the roots and shoots of lettuce are significantly lower than those under the KOH modification and the ALC composite modification (P<0.05). The possible reason for the analysis is that the repeated alkali-acid-alkali modification process significantly increases the specific surface area of the biochar, and significantly improves its pore volume and pore diameter, thus providing more binding sites for PS-NPs. Therefore, in terms of PS-NPs content, the effect of the ALCL composite modified biochar is good.

[0089] In summary, the ALCL composite modified biochar has a better effect on reducing Cd and PS-NPs in the shoots of lettuce.

[0090] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a soil additive for simultaneously reducing the accumulation of heavy metals and microplastics in vegetables, characterized in that: It includes the preparation of modified biochar and the preparation of soil additives containing modified biochar; The preparation of modified biochar includes the following steps: Step S1, pyrolysis: taking plant straw and performing pyrolysis in stages, the first pyrolysis temperature is 400-600°C, and the subsequent pyrolysis temperature is 600-800°C; Step S2, alkali modification: soak the biochar obtained in step S1 in an alkali solution, and heat and stir; Step S3, acid modification: washing the biochar obtained in step S2 until the pH is stable, and then immersing it in an acid solution and stirring; Step S4, secondary alkaline modification: washing the biochar obtained in step S3 until the pH is stable, and then immersing it in an alkaline solution for secondary alkaline modification; Step S5, washing the biochar obtained in step S4 until the pH value is stable, and drying to obtain alkali-acid-base combined modified biochar.

2. The method for preparing a soil additive for simultaneously reducing the accumulation of heavy metals and microplastics in vegetables according to claim 1, characterized in that: The plant straw is selected from the straw of wheat, rice and corn.

3. The method for preparing a soil additive for simultaneously reducing the accumulation of heavy metals and microplastics in vegetables according to claim 1, characterized in that: In the alkali modification of steps S2 and S4, a magnetic stirrer is used, the temperature of the magnetic stirrer is controlled at 60±5° C., and the stirring speed is 600-800 rpm.

4. The method for preparing a soil additive for simultaneously reducing the accumulation of heavy metals and microplastics in vegetables according to claim 1, characterized in that: In the alkaline modification of steps S2 and S4, the alkaline solution is selected from KOH, NaOH, and Ca(OH)2 solution, and the concentration is 1M-4M.

5. The method for preparing a soil additive for simultaneously reducing the accumulation of heavy metals and microplastics in vegetables according to claim 1, characterized in that: In step S3 acid modification, a magnetic stirrer is used to control stirring at room temperature, and the stirring speed is 600-800 rpm.

6. The method for preparing a soil additive for simultaneously reducing the accumulation of heavy metals and microplastics in vegetables according to claim 1, characterized in that: In step S3 of acid modification, the acid solution is a weak acid solution, including citric acid or acetic acid; the acetic acid is a 10%-40% solution.

7. The method for preparing a soil additive for simultaneously reducing the accumulation of heavy metals and microplastics in vegetables according to claim 1, characterized in that: The preparation of the soil additive containing modified biochar includes the following method: after quicklime and zeolite are crushed, ground and sieved, alkali-acid-base combined modified biochar: quicklime: zeolite are combined in a mass ratio of 6-8:1-2:1-2, and the soil additive is obtained after being fully mixed.

8. The method for preparing a soil additive for simultaneously reducing the accumulation of heavy metals and microplastics in vegetables according to claim 7, characterized in that: The mass ratio of alkali-acid combined modified biochar: quicklime: zeolite is 8:1:

1.

9. The soil additive prepared by the method for preparing a soil additive for simultaneously reducing the accumulation of heavy metals and microplastics in vegetables as described in any one of claims 1 to 8.

10. The use of the soil additive according to claim 9 in reducing the accumulation of heavy metals and microplastics in vegetables, characterized in that: The vegetables are leafy vegetables, including lettuce, rapeseed, cabbage and spinach; The heavy metals are cationic heavy metals, including Cd, Pb, Cu and Ni.

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