Geological high background soil conditioner, preparation method and application thereof

Abstract

This invention provides a soil conditioner for high geological background and its preparation method, comprising the following steps: (1) mixing and ball milling biochar and calcium oxide to obtain mixed powder one; (2) soaking attapulgite or reduced iron powder in plant extract, adding citric acid to control the pH of the reaction system between 2 and 4 and maintaining it, rinsing with a large amount of water until the pH of the rinsing solution is constant and drying to obtain mixed powder two; (3) mixing mixed powder one and mixed powder two evenly to obtain the soil conditioner, with a mixing time of less than 5 min. The high geological background soil conditioner prepared by this invention is applied to soil remediation. Without adding exogenous Se agents, it achieves the synergistic effect of stabilizing endogenous Cd and activating endogenous Se in the soil by using a low-cost, Se-free green conditioner.

Description

Technical Field

[0001] This invention relates to the field of soil remediation and environmental functional materials technology, specifically to a soil conditioner with high geological background, its preparation method, and its application. Background Technology

[0002] Soils with high geological background pollution are naturally formed, making it difficult to remove them through source control. The only way to achieve safe utilization of contaminated soil is through soil conditioning. Furthermore, in addition to being enriched in the harmful element Cd, soils with high geological background pollution typically also contain significant amounts of the beneficial element selenium (Se). How to reduce the mobility of Cd in soil while simultaneously increasing the mobility of Se through soil improvement is a crucial technical challenge for ensuring the safe utilization of soils in areas with high geological background pollution and for safe rice production.

[0003] Existing patent CN202410534432.4 relates to the field of cadmium-contaminated soil remediation technology, particularly a method for remediating cadmium-contaminated soil based on a chili-corn intercropping planting pattern. In acidic soils of southern regions, this method involves first planting chili peppers with a high Cd enrichment coefficient, followed by intercropping corn with a low Cd enrichment coefficient, coupled with double mulching to promote root development. This leverages the differences and competition in Cd accumulation within the roots to amplify the hyperaccumulation of Cd by the chili pepper roots, thereby reducing the total Cd content in the corn rhizosphere and the absorption of Cd by the corn roots. Subsequently, 100 mg / L nano-selenium is sprayed during the budding stage of chili peppers and the jointing stage of corn to further inhibit Cd absorption by chili pepper and corn kernels. Simultaneously, fertilization management is integrated throughout the entire growth period to remediate Cd-contaminated soil, resulting in a green, high-yield, efficient, and sustainable approach.

[0004] Existing patent CN202310837090.9 relates to a cadmium-controlling and selenium-enhancing organic fertilizer for acidic cadmium-contaminated soil and its preparation method, belonging to the field of agricultural technology. The raw materials of this cadmium-controlling and selenium-enhancing organic fertilizer include the following components by weight: 15-18 parts sodium selenite, 25-35 parts bamboo shoot fermentation product, 5-8 parts calcium magnesium phosphate fertilizer, 5-8 parts diammonium phosphate, 10-15 parts potassium chloride, 30-35 parts wood ash, 15-20 parts sodium humate, 0.8-1.2 parts chitosan, and 2.5-3.5 parts disodium 5′-guanylate. The organic fertilizer of this invention is rich in nutrients, has a simple and controllable preparation process, and exhibits significant cadmium-controlling and selenium-enhancing effects, making it suitable for large-scale application.

[0005] However, existing technologies only disclose methods for remediating Cd pollution and the addition of exogenous Se to treat Cd, but they cannot activate the Se activity of the soil itself in geologically high background areas. Therefore, this invention provides a method for improving geologically high background soil. Summary of the Invention

[0006] The purpose of this invention is to provide a soil conditioner with high geological background and its preparation method, which can be applied to soil remediation. Without adding exogenous Se agents, it achieves the synergistic effect of stabilizing endogenous Cd and activating endogenous Se in the soil by using a low-cost, Se-free green conditioner.

[0007] On one hand, the present invention provides a soil conditioner with high geological background, the steps of which include:

[0008] (1) The biochar and calcium oxide were mixed and ball-milled to obtain a mixed powder.

[0009] (2) Soak attapulgite or reduced iron powder in plant extract, add citric acid to control the pH of the reaction system between 2 and 4 and maintain it, filter and rinse with a lot of water until the pH of the rinsing solution is constant and dry to obtain mixed powder II.

[0010] (3) Mix the first mixed powder and the second mixed powder evenly to obtain the soil conditioner. The mixing time is less than 5 minutes.

[0011] Furthermore, the soil conditioner contains 35%-45% biochar, 30%-40% calcium oxide, and 15%-35% attapulgite or reduced iron powder soaked in plant extract.

[0012] Furthermore, the soil conditioner contains 40% biochar, 30%-40% calcium oxide, and the remainder is attapulgite or reduced iron powder soaked in plant extract.

[0013] Furthermore, in step (1), the raw material for preparing biochar is corn cob or rice straw, the burning temperature is 300-500℃, and the temperature holding time is 1-2h.

[0014] Furthermore, in step (1), the ball milling is performed with nitrogen gas and at 200-300 rpm for 1-2 hours.

[0015] Furthermore, in step (2), the attapulgite or reduced iron powder is 80-120 mesh.

[0016] Further, the method for preparing the plant extract in step (2) includes: placing at least one fruit peel selected from 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℃ for 10-12h, and filtering for later use.

[0017] 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.

[0018] Furthermore, the first mixed powder and the second mixed powder are mixed on-site before use to prevent excessive heat generation during the mixing process of calcium oxide and attapulgite / iron powder.

[0019] On the other hand, the present invention also provides a soil conditioner with high geological background, which is prepared using the aforementioned method.

[0020] Furthermore, the method of using the soil conditioner includes: applying it to the soil surface layer 0-20cm below the surface 3-7 days before transplanting, at a rate of 1-10t / ha.

[0021] 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 attapulgite is used, and the dosage of the soil conditioner added to the soil is 2-5 t / ha.

[0022] Furthermore, when the Cd content in the soil is <0.5mg / kg and the Se content in the soil is ≥5mg / kg, a soil conditioner containing attapulgite is used, and the dosage of the soil conditioner added to the soil is 1-2t / ha.

[0023] Furthermore, when the Cd content in the soil is ≥0.5mg / kg and the Se content in the soil is <5mg / kg, a soil conditioner containing reduced iron powder is used, and the dosage of the soil conditioner added to the soil is 5-10t / ha.

[0024] Furthermore, when the Cd content in the soil is ≥0.5mg / kg and the Se content in the soil is ≥5mg / kg, a soil conditioner containing reduced iron powder is used, and the dosage of the soil conditioner added to the soil is 2-5t / ha;

[0025] Furthermore, the soil conditioner is applied to paddy fields where rice is grown.

[0026] On the other hand, the soil conditioner with high geological background and its preparation method in this invention are applied to soil remediation.

[0027] 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.

[0028] The soil is a geologically high background soil located in southwestern 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 parent materials, and is enriched with both Cd and Se.

[0029] The beneficial effects of this invention are as follows:

[0030] This invention provides a soil conditioner, in which the plant extract is rich in phenolic substances, which can enhance the stabilization of heavy metals while washing away impurities on the surface of attapulgite soil and reduced iron powder. It is a green synthesis method. Citric acid is a low molecular weight organic acid secreted by plant roots and native soil microorganisms in nature. It is an environmentally friendly weak acid. Its use in the green modification of materials can play a role in expanding pores. The materials with expanded pores enhance the stabilization effect of heavy metals through enhanced adsorption.

[0031] High background geological conditions typically involve the accumulation of selenium (Se) in the soil, but its bioavailability is very low, making it difficult for plants to absorb and utilize. This invention addresses this issue by adding a soil conditioner to high background geological soils, without involving the addition of exogenous Se-containing agents. This method simultaneously achieves Cd stabilization and Se activation, enabling the safe production and utilization of such soils. Furthermore, the method of using the soil conditioner in this invention employs a green, sustainable, and low-cost Se-free agent to stimulate the activity of the soil's own endogenous Se.

[0032] The soil conditioner in this invention can stabilize Cd and activate endogenous Se. Excessively high or low Se content in rice can have negative effects on the human body. Therefore, the method of using the soil conditioner in this invention can reduce the Cd content of rice to below 0.20 mg / kg while maintaining the Se content of the crop within a reasonable and narrow range, specifically between 0.04 and 0.30 mg / kg. Maintaining the Se content within this range allows the human body to supplement beneficial Se elements through the intake of Se-rich rice without causing Se excess and thus avoiding negative effects. Detailed Implementation

[0033] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] Example 1

[0035] Several soil samples from a geologically high background paddy field in southwestern my country, where carbonate and clastic rocks are combined, were selected (Cd ranged from 0.3 to 0.7 mg / kg in different soils; Se ranged from 4.2 to 6.6 mg / kg in different soils). Two soil conditioners were prepared and related studies were conducted.

[0036] This embodiment provides a soil conditioner for high geological background soils, the preparation steps of which include:

[0037] Corn cobs were selected as biomass feedstock and pyrolyzed at 300℃ for 2 hours. Rice straw was also selected as biomass feedstock and pyrolyzed at 500℃ for 2 hours. 100-mesh attapulgite and 100-mesh reduced iron powder were used for modification of the plant extract.

[0038] Preparation of plant extract from watermelon rind: Place dried watermelon rind in deionized water at a solid-liquid ratio of 1g:10mL, mix at 40℃ for 12h, and filter for later use.

[0039] 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. Citric acid was added to control the pH of the reaction system at 3 and maintained for another hour. After filtration, the solution was rinsed with plenty of water until the pH of the rinsing solution was constant. The solution was then dried at 40°C.

[0040] Formula 1: 40% corn cob biochar, 30% calcium oxide, and 30% attapulgite modified by soaking in plant extract.

[0041] 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%.

[0042] In both formulations, biochar and calcium oxide were mixed using ball milling under a nitrogen atmosphere at a speed of 300 rpm for 1 hour. After ball milling, the mixture of 1) biochar and calcium oxide and 2) attapulgite / reduced iron powder modified by soaking in plant extract were mixed on-site for 3 minutes and then added to the soil.

[0043] The method of applying the soil conditioner is to add the material 3 days before transplanting, and apply it to the soil surface layer 20cm below the soil surface.

[0044] Rice grains were collected and digested at maturity, and the contents of Cd and Se in the rice grains were tested by ICP-MS. The contents of rice were determined from 10 rice plants. The results of different formulations are as follows:

[0045]

[0046]

[0047] Note: In the table above, "Formula 1" consists of 40% corn cob biochar, 30% calcium oxide, and 30% attapulgite modified by soaking in plant extract; "Formula 2" consists of 40% rice straw biochar, 40% calcium oxide, and 20% reduced iron powder modified by soaking in plant extract.

[0048] Comparative Example 1

[0049] The formulation is the same as in Example 1, but the dosage is changed. Specifically, the dosage is reduced under the same formulation conditions. It can be found that the Cd stabilization effect is worse and cannot meet the limit requirement of 0.2 mg / kg.

[0050]

[0051]

[0052] Comparative Example 2

[0053] The formula is the same as in Example 1, but the dosage is changed. Specifically, the dosage is increased under the same formula conditions. It can be found that Se is over-activated (Se content in rice is greater than 0.3 mg / kg), which may pose a risk to human health.

[0054]

[0055] Comparative Example 3

[0056] Using soil with 0.4 mg / kg Cd and 5.6 mg / kg Se from Example 1, and applying Formula 1 at 2 t / ha, but replacing the biomass with chicken manure, silkworm manure, and cow manure (animal-derived biomass), it was found that the Cd content in the rice was greater than 0.2 mg / kg (0.27, 0.31, and 0.35 mg / kg, respectively), indicating poor stabilization effect.

[0057] Comparative Example 4

[0058] Using soil with 0.4 mg / kg Cd and 5.6 mg / kg Se from Example 1, and formula 1 at 2 t / ha, but omitting the soaking step of plant extract, 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.

[0059] Comparative Example 5

[0060] Using soil with 0.4 mg / kg Cd and 5.6 mg / kg Se from Example 1, and formula 1 at 2 t / ha, but omitting the step of adding citric acid to control pH, 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.

[0061] Comparative Example 6

[0062] Using soil with 0.7 mg / kg Cd and 6.6 mg / kg Se from Example 1, and formula 2 at 5 t / ha, but omitting the soaking step of 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.

[0063] Comparative Example 7

[0064] Using soil with 0.7 mg / kg Cd and 6.6 mg / kg Se from Example 1, and formula 2 with 5 t / ha, but omitting the step of adding citric acid to control pH, 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.

[0065] Comparative Example 8

[0066] Using soil with 0.4 mg / kg Cd and 5.6 mg / kg Se from Example 1, and formula 1 at 2 t / ha, but omitting the ball milling step and simply mixing biochar and calcium oxide 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.

[0067] Comparative Example 9

[0068] Using soil with 0.7 mg / kg Cd and 6.6 mg / kg Se from Example 1, and formula 2 with 5 t / ha, but omitting the ball milling step and simply mixing biochar and calcium oxide 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.

[0069] Comparative Example 10

[0070] Using soil with 0.4 mg / kg Cd and 5.6 mg / kg Se as described in Example 1, the biochar content was increased to 50% while other conditions remained unchanged. The Se content in the rice was found to be 0.45 mg / kg (greater than 0.3 mg / kg). This is because biochar is alkaline, and excessive addition caused the alkali solubility of Se.

[0071] Comparative Example 11

[0072] Using soil with 0.4 mg / kg Cd and 5.6 mg / kg Se as described in Example 1, and increasing the calcium oxide content to 45% while keeping other conditions unchanged, the Se content in rice was found to be 0.42 mg / kg (greater than 0.3 mg / kg). This is because calcium oxide is alkaline, and excessive addition caused the alkali solubility of Se.

[0073] Comparative Example 12

[0074] Using soil with 0.4 mg / kg Cd and 5.6 mg / kg Se as described in Example 1, the biochar content was reduced to 30% while other conditions remained unchanged. It was found that the Cd content in rice was 0.37 mg / kg (greater than 0.2 mg / kg), which did not achieve the desired stabilization effect.

[0075] Comparative Example 13

[0076] Using soil with 0.4 mg / kg Cd and 5.6 mg / kg Se as described in Example 1, the proportion of calcium oxide was reduced to 25%, while 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 desired stabilization effect.

[0077] 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 modifications or equivalent substitutions can still be made to the present invention; and all technical solutions and improvements that do not depart from the spirit and scope of the present invention should be covered within the scope of the claims of the present invention.

Claims

1. A method for preparing a soil conditioner with high geological background, wherein the high geological background soil has a Cd content greater than the global average of 0.36 mg / kg and a Se content greater than the global average of 0.32 mg / kg, characterized in that the steps include... include: (1) The biochar and calcium oxide were mixed and ball-milled to obtain a mixed powder. (2) Soak attapulgite or reduced iron powder in plant extract, add citric acid to it, keep the pH of the reaction system between 2 and 4, filter it, rinse it with a lot of water until the pH of the rinsing solution is constant, and dry it to obtain mixed powder II. (3) Mix the first mixed powder and the second mixed powder evenly to obtain the soil conditioner. The mixing time should be less than 5 minutes. The soil conditioner contains 35%-45% biochar, 30%-40% calcium oxide, and 15%-35% attapulgite or reduced iron powder soaked in plant extract. In step (1), the raw material for preparing biochar is corn cob or rice straw, the burning temperature is 300-500℃, and the temperature holding time is 1-2h. The preparation method of the plant extract in step (2) includes: placing dried watermelon rind in deionized water with a solid-liquid ratio of 1g:(5-10)mL, then mixing at 30-50℃ for 10-12h, and filtering for later use; In step (2), the soaking time is 1-2 hours, the holding time is 1-2 hours, and the drying temperature is 30-50℃.

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

3. A soil conditioner with high geological background, characterized in that, It is prepared using the preparation method described in claim 1 or 2.

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