Geological high-background soil conditioner as well as preparation method and application thereof

Abstract

The invention provides a geological high-background soil conditioner and a preparation method thereof. The preparation method comprises the following steps: (1) mixing and ball-milling biochar and calcium oxide to obtain mixed powder I; (2) soaking attapulgite or reduced iron powder in a plant extracting solution, adding citric acid into the plant extracting solution to control the pH value of a reaction system to be 2-4, keeping the pH value, flushing with a large amount of water until the pH value of a flushing solution is constant, and drying to obtain mixed powder II; and (3) uniformly mixing the obtained mixed powder I and the obtained mixed powder II to obtain the soil conditioner, wherein the mixing time is less than 5 minutes. The geological high-background soil conditioner prepared by the invention is applied to soil remediation, and under the condition that an exogenous Se agent is not added, a green conditioner which is low in cost and does not contain Se is adopted, so that the synergistic effect of stabilization of endogenous Cd in soil and activation of endogenous Se is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of soil remediation and environmental functional materials, and in particular to a geological high-background soil conditioner and a preparation method and application thereof. Background Art

[0003] Since geological high-background soils are naturally formed, it is difficult to remove soil pollution by source prevention and control. The only way to achieve safe utilization of contaminated soil is through soil conditioning. In addition, in addition to being enriched with harmful elements such as Cd, geological high-background soils are usually also enriched with more beneficial elements such as selenium (Se). How to reduce the mobility of soil Cd while increasing the mobility of soil Se through soil improvement is an important technical issue for achieving safe utilization of soil in geological high-background areas and safe rice production.

[0004] The existing patent CN202410534432.4 relates to the technical field of cadmium-contaminated soil remediation, especially a method for remediating cadmium-contaminated soil based on the pepper-corn intercropping model; in the acidic soil in the south, by first planting peppers with a high Cd enrichment coefficient and then intercropping corn with a low Cd enrichment coefficient, combined with double-film measures, the root system of crops is promoted to develop, and the difference in root Cd accumulation and competitive relationship are used to amplify the super-enrichment effect of the pepper root system on Cd, thereby reducing the total amount of Cd in the rhizosphere soil of corn and the absorption of Cd by the root system; then, 100 mg / L nano-selenium is sprayed during the pepper budding period and the corn jointing period to further block the absorption of Cd by peppers and corn grains; at the same time, fertilization management is combined with the entire growth period to repair Cd-contaminated soil, which is green, high-yield, efficient and sustainable.

[0005] The existing patent CN202310837090.9 relates to an organic fertilizer for controlling cadmium and increasing selenium in acidic cadmium-contaminated soil and its preparation method, which relates to the field of agricultural technology. The raw materials of the organic fertilizer for controlling cadmium and increasing selenium in the invention include the following mass components: 15-18 parts of sodium selenite, 25-35 parts of bamboo shoot fermentation, 5-8 parts of calcium magnesium phosphate fertilizer, 5-8 parts of diammonium phosphate, 10-15 parts of potassium chloride, 30-35 parts of plant ash, 15-20 parts of sodium humate, 0.8-1.2 parts of chitosan and 2.5-3.5 parts of disodium 5′-guanylate. The organic fertilizer in the present invention is rich in nutrients, has a simple and controllable preparation process, has a significant effect of controlling cadmium and increasing selenium, and is suitable for large-scale promotion and application.

[0006] However, the prior art only discloses a method for repairing Cd pollution and adding exogenous Se to achieve Cd control, but cannot achieve the stimulation of Se activity in the soil of the geological high background area. Based on this, the present invention provides a method for improving geological high background soil. Summary of the invention

[0007] The purpose of the present invention is to provide a geological high-background soil conditioner and a preparation method thereof, which are applied to soil remediation. Without adding exogenous Se agents, a low-cost, Se-free green conditioner is adopted to achieve the synergistic effect of stabilizing endogenous Cd in the soil and activating endogenous Se.

[0008] In one aspect, the present invention provides a geological high background soil conditioner, comprising the steps of:

[0009] (1) mixing biochar and calcium oxide by ball milling to obtain a mixed powder;

[0010] (2) placing attapulgite or reduced iron powder in a plant extract and soaking it, adding citric acid thereto to control and maintain the pH of the reaction system between 2 and 4, filtering and washing with a large amount of water until the pH value of the washing liquid is constant, and drying to obtain a mixed powder II;

[0011] (3) The mixed powder 1 and the mixed powder 2 are mixed evenly to obtain a soil conditioner, and the mixing time is less than 5 minutes.

[0012] Furthermore, in the soil conditioner, biochar accounts for 35%-45%, calcium oxide accounts for 30%-40%, and attapulgite or reduced iron powder soaked in plant extract accounts for 15%-35%.

[0013] Furthermore, the soil conditioner contains 40% biochar, 30%-40% calcium oxide, and the remainder is attapulgite or reduced iron powder soaked in plant extract.

[0014] Furthermore, in step (1), the raw material for preparing biochar is corn cob or rice straw, the firing temperature is 300-500° C., and the temperature is maintained for 1-2 hours.

[0015] Furthermore, in the step (1), the ball milling is carried out under nitrogen gas flow and at 200-300 rpm for 1-2 hours.

[0016] Furthermore, in the step (2), the attapulgite or reduced iron powder has a mesh size of 80-120.

[0017] Furthermore, the preparation method of the plant extract in step (2) comprises: placing at least one of dried watermelon peel, banana peel, orange peel and grapefruit peel in deionized water with a solid-liquid ratio of 1g:(5-10)mL, then mixing at 30-50°C for 10-12h, filtering and setting aside.

[0018] Furthermore, in step (2), the soaking time is 1-2 hours; the holding time is 1-2 hours; and the drying temperature is 30-50°C.

[0019] Furthermore, the mixed powder 1 and the obtained mixed powder 2 are mixed at the adding site before use to prevent excessive heat release during the mixing process of calcium oxide and attapulgite / iron powder.

[0020] On the other hand, the present invention also provides a geological high-background soil conditioner prepared by the above method.

[0021] Furthermore, the method for using the soil conditioner includes: adding it to the soil surface 0-20 cm below 3-7 days before transplanting, with an addition amount of 1-10 t / ha.

[0022] Furthermore, when the Cd content in the soil is less than 0.5 mg / kg and the Se content in the soil is less than 5 mg / kg, a soil conditioner containing attapulgite is used, and the amount of the soil conditioner added to the soil is 2-5 t / ha;

[0023] Furthermore, when the Cd content in the soil is less than 0.5 mg / kg and the Se content in the soil is ≥ 5 mg / kg, a soil conditioner containing attapulgite is used, and the amount of the soil conditioner added to the soil is 1-2 t / ha;

[0024] Furthermore, when the Cd content in the soil is ≥0.5 mg / kg and the Se content in the soil is <5 mg / kg, a soil conditioner containing reduced iron powder is used, and the amount of the soil conditioner added to the soil is 5-10 t / ha;

[0025] Furthermore, when the Cd content in the soil is ≥0.5 mg / kg and the Se content in the soil is ≥5 mg / kg, a soil conditioner containing reduced iron powder is used, and the amount of the soil conditioner added to the soil is 2-5 t / ha;

[0026] Furthermore, the soil conditioner is applied to paddy fields where rice is grown.

[0027] On the other hand, the geological high background soil conditioner and the preparation method thereof in the present invention are used in soil remediation.

[0028] Furthermore, the Cd content in the soil is greater than the global average of 0.36 mg / kg, and the Se content in the soil is greater than the global average of 0.32 mg / kg.

[0029] The soil is a geological high-background soil located in the southwest of my country. It is formed by the weathering of carbonate rocks (limestone or dolomite), clastic sedimentary rocks (such as black shale) or Quaternary sediments as soil parent materials, and is enriched in Cd and Se.

[0030] The beneficial effects of the present invention are:

[0031] The present invention provides a soil conditioner, wherein the plant extract is rich in phenolic substances, and can wash away impurities on the surfaces of attapulgite and reduced iron powder while enhancing the heavy metal stabilization capability, and is a green synthesis method; citric acid is a low molecular weight organic acid secreted by plant roots, soil indigenous microorganisms, etc. in nature, and is an environmentally friendly weak acid, and can be used for green modification of materials to expand pores, and the expanded materials can enhance the stabilization effect of heavy metals through enhanced adsorption;

[0032] The geological high background area usually has a large amount of Se element enriched in the soil, but its biological effectiveness is very low and it is difficult to be absorbed and utilized by plants. The present invention constructs a method for simultaneously realizing Cd stabilization and Se activation by adding a soil conditioner to the geological high background soil without involving the addition of exogenous Se agents, which can realize the safe production and utilization of the geological high background soil; the method for using the soil conditioner in the present invention is green, sustainable, low-cost and does not contain Se agents, and realizes the stimulation of the endogenous Se activity of the soil itself.

[0033] The soil conditioner of the present invention can achieve Cd stabilization and endogenous Se activation. Too high or too low Se content in rice will cause certain negative effects on the human body. Therefore, the use method of the soil conditioner of the present invention can reduce the Cd content of rice to below 0.20 mg / kg while keeping the Se content of the crop within a reasonable narrow range, which is between 0.04-0.30 mg / kg. Keeping the Se content within this range can enable the human body to supplement the beneficial Se element by ingesting Se-rich rice, without causing excess Se elements, thereby causing negative effects. DETAILED DESCRIPTION

[0034] The technical solution of the present invention is described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0035] Example 1

[0036] Several soils from a paddy field with a high geological background where carbonate rocks and clastic rocks are distributed in southwest my country were selected (the Cd content in different soils ranges from 0.3 to 0.7 mg / kg; the Se content in different soils ranges from 4.2 to 6.6 mg / kg), and two soil conditioners were prepared and related research was carried out.

[0037] This embodiment provides a geological high background soil conditioner, the preparation steps of which include:

[0038] Corn cobs were selected as biomass raw materials and pyrolyzed at 300°C for 2 h. Rice straw was also selected as biomass raw materials and pyrolyzed at 500°C for 2 h. 100-mesh attapulgite and 100-mesh reduced iron powder were selected for plant extract modification.

[0039] Prepare plant extract using watermelon rind: place dry watermelon rind in deionized water with a solid-liquid ratio of 1 g:10 mL, then mix at 40°C for 12 hours and filter for later use.

[0040] 100 mesh attapulgite and 100 mesh reduced iron powder were soaked in plant extract at a solid-liquid ratio of 1:20 (g:ml) for 1 hour, and the solid-liquid ratio was 1g:20mL; citric acid was added to control the pH of the reaction system at 3, and then maintained for 1 hour. After filtering, it was rinsed with a large amount of water until the pH of the rinse liquid was constant, and dried at 40°C.

[0041] Formula 1: 40% corn cob biochar, 30% calcium oxide, and 30% attapulgite modified by soaking in plant extract.

[0042] Formula 2: Rice straw biochar accounts for 40%, calcium oxide accounts for 40%, and reduced iron powder modified by soaking in plant extract accounts for 20%.

[0043] In both formulations, the biochar and calcium oxide mixture was ball-milled under nitrogen atmosphere at a speed of 300 rpm for 1 h. After ball-milling, 1) the mixture of biochar and calcium oxide and 2) the modified attapulgite / reduced iron powder soaked in plant extract were mixed at the dosing site for 3 min and then added to the soil.

[0044] The method of using soil conditioner is to add the material 3 days before transplanting, 20 cm below the soil surface.

[0045] Rice grains were collected and digested during the rice maturity period, and the Cd and Se contents in the rice grains were tested by ICP-MS, where the rice contents were the results of the content determination of 10 rice plants. The results of different samples are as follows:

[0046]

[0047]

[0048] Note: In the above table, “Formula 1” all consisted of 40% corn cob biochar, 30% calcium oxide, and 30% attapulgite modified by soaking in plant extracts; “Formula 2” all consisted of 40% rice straw biochar, 40% calcium oxide, and 20% reduced iron powder modified by soaking in plant extracts.

[0049] Comparative Example 1

[0050] The formula is the same as that in Example 1, but the dosage is changed. Specifically, the dosage is reduced accordingly under the same formula conditions. It can be found that the Cd stabilization effect is deteriorated and the limit requirement of 0.2 mg / kg cannot be reached.

[0051]

[0052]

[0053] Comparative Example 2

[0054] The formula is the same as that in Example 1, but the dosage is changed. Specifically, the dosage is increased accordingly under the same formula conditions. It can be found that Se is over-activated (the Se content of rice is greater than 0.3 mg / kg), which may be risky to human health.

[0055]

[0056] Comparative Example 3

[0057] Using the soil with 0.4 mg / kg Cd and 5.6 mg / kg Se in Example 1, 2 t / ha of Formula 1 was used, but the biomass was replaced with chicken manure, silkworm manure, and cow manure (animal-derived biomass). It was found that the Cd content of rice was greater than 0.2 mg / kg (0.27, 0.31, and 0.35 mg / kg, respectively), and the stabilization effect was poor.

[0058] Comparative Example 4

[0059] Using the soil with 0.4 mg / kg Cd and 5.6 mg / kg Se in Example 1, 2 t / ha of Formulation 1 was used, but the soaking step of the plant extract was omitted. It was found that the Cd content of rice was 0.26 mg / kg (greater than 0.2 mg / kg), and the stabilization effect was poor.

[0060] Comparative Example 5

[0061] Using the soil with 0.4 mg / kg Cd and 5.6 mg / kg Se in Example 1, 2 t / ha of Formulation 1 was used, but the step of adding citric acid to control pH was omitted. It was found that the Cd content of rice was 0.33 mg / kg (greater than 0.2 mg / kg), and the stabilization effect was poor.

[0062] Comparative Example 6

[0063] Using the soil with 0.7 mg / kg Cd and 6.6 mg / kg Se in Example 1, using Formulation 2 at 5 t / ha, but omitting the soaking step of the plant extract, it was found that the Cd content of rice was 0.37 mg / kg (greater than 0.2 mg / kg), and the stabilization effect was poor.

[0064] Comparative Example 7

[0065] Using the soil with 0.7 mg / kg Cd and 6.6 mg / kg Se in Example 1, 5 t / ha of Formulation 2 was used, but the step of adding citric acid to control pH was omitted. It was found that the Cd content of rice was 0.26 mg / kg (greater than 0.2 mg / kg), and the stabilization effect was poor.

[0066] Comparative Example 8

[0067] Using the soil containing 0.4 mg / kg Cd and 5.6 mg / kg Se in Example 1, 2 t / ha of Formulation 1 was used, but the ball milling step was omitted. In the mixture, the biochar and calcium oxide were simply mixed by manual stirring. It was found that the Cd content of rice was 0.30 mg / kg (greater than 0.2 mg / kg), and the stabilization effect was poor.

[0068] Comparative Example 9

[0069] Using the soil with 0.7 mg / kg Cd and 6.6 mg / kg Se in Example 1, 5 t / ha of Formulation 2 was used, but the ball milling step was omitted. In the mixture, the biochar and calcium oxide were simply mixed by manual stirring. It was found that the Cd content of rice was 0.28 mg / kg (greater than 0.2 mg / kg), and the stabilization effect was poor.

[0070] Comparative Example 10

[0071] Using the soil with 0.4 mg / kg Cd and 5.6 mg / kg Se in Example 1, the proportion of biochar was increased to 50%, and other conditions remained unchanged. It was found that the Se content of rice was 0.45 mg / kg (greater than 0.3 mg / kg). This is because biochar is alkaline, and excessive addition causes alkali dissolution of Se elements.

[0072] Comparative Example 11

[0073] Using the soil with 0.4 mg / kg Cd and 5.6 mg / kg Se in Example 1, the calcium oxide ratio was increased to 45%, and other conditions remained unchanged. It was found that the Se content of rice was 0.42 mg / kg (greater than 0.3 mg / kg). This is because calcium oxide is alkaline, and excessive addition causes alkali dissolution of Se elements.

[0074] Comparative Example 12

[0075] Using the soil with 0.4 mg / kg Cd and 5.6 mg / kg Se in Example 1, the proportion of biochar was reduced to 30%, and other conditions remained unchanged. It was found that the Cd content of rice was 0.37 mg / kg (greater than 0.2 mg / kg), which did not achieve the ideal stabilization effect.

[0076] Comparative Example 13

[0077] Using the soil containing 0.4 mg / kg Cd and 5.6 mg / kg Se in Example 1, the proportion of calcium oxide was reduced to 25%, and other conditions remained unchanged. It was found that the Cd content of rice was 0.31 mg / kg (greater than 0.2 mg / kg), which did not achieve the ideal stabilization effect.

[0078] Finally, it should be noted that the above embodiments are only used to illustrate the present invention and are not intended to limit the technical solutions described in the present invention. Those skilled in the art should understand that the present invention can still be modified or replaced by equivalents. All technical solutions and improvements that do not depart from the spirit and scope of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A method for preparing a geological high background soil conditioner, characterized in that the steps include: (1) mixing biochar and calcium oxide by ball milling to obtain a mixed powder; (2) placing attapulgite or reduced iron powder in a plant extract and soaking it, adding citric acid thereto to control the pH of the reaction system to be between 2 and 4 and maintaining it, filtering and washing with a large amount of water until the pH value of the washing liquid is constant, and drying to obtain a mixed powder II; (3) The mixed powder 1 and the mixed powder 2 are mixed evenly to obtain a soil conditioner, and the mixing time is less than 5 minutes.

2. The method for preparing a geological high background soil conditioner according to claim 1, characterized in that: The soil conditioner comprises 35%-45% of biochar, 30%-40% of calcium oxide, and 15%-35% of attapulgite or reduced iron powder soaked in plant extract.

3. The method for preparing a geological high background soil conditioner according to claim 1, characterized in that: In the step (1), the raw material for preparing biochar is corn cob or rice straw, the firing temperature is 300-500° C., and the temperature is maintained for 1-2 hours.

4. The method for preparing a geological high background soil conditioner according to claim 1, characterized in that: In the step (1), the ball milling is carried out under nitrogen gas flow and at 200-300 rpm for 1-2 hours.

5. The method for preparing a geological high background soil conditioner according to claim 1, characterized in that: The preparation method of the plant extract in step (2) comprises: placing at least one of dried watermelon peel, banana peel, orange peel and grapefruit peel in deionized water with a solid-liquid ratio of 1 g: (5-10) mL, then mixing at 30-50° C. for 10-12 hours, filtering and setting aside.

6. The method for preparing a geological high background soil conditioner according to claim 1, characterized in that: In the step (2), the soaking time is 1-2 hours; the holding time is 1-2 hours; and the drying temperature is 30-50°C.

7. A geological high background soil conditioner, characterized in that: The method is prepared by any one of claims 1 to 6.

8. A geological high background soil conditioner according to claim 7, characterized in that: The method for using the soil improver comprises: adding the soil improver to the soil surface 0-20 cm below the soil surface 3-7 days before transplanting, with an addition amount of 1-10 t / ha.

9. A method for preparing the geological high background soil conditioner according to any one of claims 1 to 6 or use of the geological high background soil conditioner according to claim 7 in soil remediation.

10. The use according to claim 9, characterized in that The Cd content in the soil is greater than the global average of 0.36 mg / kg, and the Se content in the soil is greater than the global average of 0.32 mg / kg.

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