Soil conditioner and preparation method thereof

Abstract

The invention discloses a soil conditioner and a preparation method thereof, and relates to the technical field of soil improvement. The preparation method comprises the following steps: mixing diatomite with a hydrochloric acid solution, heating and stirring for reaction, performing suction filtration, washing with deionized water until filtrate is neutral, and drying and grinding to obtain purified diatomite; dissolving magnesium chloride hexahydrate, aluminum chloride hexahydrate and urea in deionized water to form a salt-urea mixed solution, adding purified diatomite for dispersion, and carrying out hydrothermal reaction, cooling, suction filtration, hot deionized water washing and drying on the turbid liquid to obtain a layered double hydroxide-diatomite composite material; the composite material is dispersed in a Tris-HCl buffer solution, dopamine hydrochloride is added under stirring for a reaction, suction filtration, deionized water washing and drying are performed after the reaction, and the soil conditioner is obtained. The modifier prepared by the invention can efficiently fix anionic and cationic heavy metals in soil, and is good in stability.

Description

Technical Field

[0001] This invention relates to the field of soil improvement technology, belonging to patent classification number C05G3 / 80, specifically to a soil conditioner and its preparation method. Background Technology

[0002] With the acceleration of industrialization and agricultural intensification, human activities such as mining, sewage irrigation, and overuse of chemical fertilizers and pesticides have led to the continuous infiltration of heavy metals into the soil. This not only damages the soil aggregate structure and inhibits microbial activity, causing soil fertility decline, but also accumulates through the "soil-crop-human" food chain, seriously threatening the quality and safety of agricultural products and human health. Soil heavy metal pollution has become one of the core environmental problems restricting the sustainable development of agriculture.

[0003] Currently, incorporating soil conditioners as functional ingredients into organic fertilizers is a mainstream technical approach that balances soil remediation and fertility enhancement. The core requirement is the efficient and stable removal and fixation of heavy metals in the soil. Among numerous potential adsorbent materials, diatomaceous earth, with its rich pore structure and large specific surface area, possesses natural heavy metal adsorption potential and has become a research hotspot in the field of soil conditioners. However, natural diatomaceous earth has significant technical shortcomings: on the one hand, it has a small number of surface active groups and a limited number of adsorption sites, resulting in a limited adsorption capacity for heavy metals, with a removal rate typically less than 50% in practical applications; on the other hand, the binding force between natural diatomaceous earth and heavy metals is weak, and after adsorption, it is easily desorbed by rainwater leaching and tillage disturbance, leading to the re-release of heavy metals. This makes long-term fixation impossible and fails to meet the long-term needs for safe utilization of farmland soil. Summary of the Invention

[0004] The purpose of this invention is to provide a soil conditioner and its preparation method to solve the technical problems mentioned in the background section. The soil conditioner prepared by this invention has a good long-term immobilization effect on heavy metals, thereby meeting the long-term needs for safe soil utilization.

[0005] To achieve the above objectives, the present invention provides the following technical solution: A method for preparing a soil conditioner includes the following steps: S1. Mix diatomaceous earth with hydrochloric acid solution, heat and stir to react. After the reaction is complete, filter and wash with deionized water until the filtrate is neutral. Then dry and grind to obtain purified diatomaceous earth. S2. Dissolve magnesium chloride hexahydrate, aluminum chloride hexahydrate and urea in deionized water to form a salt-urea mixed solution. Then add purified diatomaceous earth and disperse it. Then carry out a hydrothermal reaction of the suspension. After the reaction is completed, cool naturally and filter. Wash the solid product with hot deionized water and dry to obtain a layered double hydroxide-diatomaceous earth composite material. S3. The layered double hydroxide-diatomaceous earth composite material was dispersed in Tris-HCl buffer solution, and dopamine hydrochloride was added under stirring to carry out the reaction. After the reaction was completed, the mixture was filtered, the solid product was washed with deionized water and dried to obtain the soil conditioner.

[0006] In this invention, a layered double hydroxide is grown in situ on the surface of acid-washed diatomaceous earth using a hydrothermal method. Its main function is to significantly enhance the fixation capacity for anionic heavy metals. The core principle lies in its unique layered structure and "memory effect." The layered double hydroxide consists of positively charged metal hydroxide layers and anions with balanced charges between the layers. When treating heavy metals such as Cr(VI), which are commonly found in the environment in anionic form (e.g., Cr2O7), this method is particularly effective. 2- During adsorption, the anions between the layers of the layered double hydroxide can undergo efficient ion exchange with these heavy metal anions, capturing and immobilizing them between the layers. Furthermore, during adsorption, the layered double hydroxide structure exhibits a strong "memory effect" for the target anions; that is, its layer structure reconfigures to preferentially accommodate and lock specific heavy metal anions. This technology transforms diatomaceous earth from a physical adsorption carrier into a material with highly efficient ion exchange capabilities, specifically addressing the technical problem of diatomaceous earth's weak ability to immobilize anionic heavy metals.

[0007] On the other hand, through the oxidative self-polymerization of dopamine, a polydopamine coating is firmly grafted onto the surface of the layered double hydroxide-diatomaceous earth composite material. Its main function is to significantly enhance the chelation and capture capacity for cationic heavy metals. The polydopamine molecule contains abundant catechol and amino groups, which are strong coordinating functional groups. When treating cationic heavy metals such as Pb(II), these functional groups act as Lewis bases, undergoing strong coordination reactions with the heavy metal cations to form stable five- or six-membered cyclic chelates. This firmly fixes the heavy metal ions to the polydopamine coating surface, effectively constructing a high-density, non-selective organic chelating network on the material surface. This compensates for the insufficient cation adsorption capacity of the layered double hydroxide-diatomaceous earth composite material, achieving broad-spectrum and efficient removal of cationic heavy metals from soil.

[0008] Preferably, in step S1, the concentration of the hydrochloric acid solution is 2–5 mol / L.

[0009] As a preferred option, in step S1, the heating temperature is 80–90°C and the reaction time is 40–60 min.

[0010] As a preferred step, in step S2, the mass ratio of magnesium chloride hexahydrate, aluminum chloride hexahydrate, and urea is 10:5-7:2-4.

[0011] As a preferred option, the hydrothermal reaction time in step S2 is 15–20 h.

[0012] As a preferred step, in step S3, the layered double hydroxide-diatomite composite material undergoes a modification treatment, including the following steps: S31. Add the epoxy silane coupling agent to a mixed solution of ethanol and water, heat and stir to hydrolyze, and obtain the hydrolysate; S32. The layered double hydroxide-diatomite composite material is added to the hydrolysate, heated and stirred to react, and then centrifuged, washed and dried to obtain the epoxy-based layered double hydroxide-diatomite composite material. S33. Polyethyleneimine is added to deionized water and stirred to dissolve, thus obtaining a polyethyleneimine solution. Epoxy-based layered double hydroxide-diatomaceous earth composite material is added to the polyethyleneimine solution, heated and stirred to react, and then centrifuged, washed, and dried to obtain the final product.

[0013] In this invention, the team discovered that grafting a polydopamine coating onto the surface of a layered double hydroxide-diatomaceous earth composite material during the oxidative self-polymerization of dopamine provides abundant cationic chelating sites. However, the polydopamine layer tends to densely coat the surface of the composite material, easily blocking interlayer channels and active sites, resulting in a shielding effect and severely weakening the inherent adsorption capacity of the composite material for anionic heavy metals. To further address this problem, this invention grafts hyperbranched polyethyleneimine (PEI) with a three-dimensional branched structure onto the surface of the composite material using an epoxy-silane coupling agent. The abundant amino functional groups in the PEI molecular chain then controllably react with dopamine, guiding it to construct an open, porous three-dimensional network structure on the material surface, rather than allowing dopamine to self-polymerize into a dense film. This avoids blocking the interlayer channels and active sites of the composite material, thus better achieving the soil conditioner's fixation effect on anionic heavy metals.

[0014] Preferably, in step S32, the mass ratio of the layered double hydroxide-diatomaceous earth composite material to the epoxy silane coupling agent is 10:0.5-2.

[0015] Preferably, in step S33, the mass ratio of the epoxy-layered double hydroxide-diatomite composite material to polyethyleneimine is 10:3 to 6.

[0016] Preferably, in step S3, the reaction temperature is 30-35℃ and the reaction time is 8-10h.

[0017] A soil conditioner is prepared by the method described above.

[0018] Compared with the prior art, the beneficial effects of the present invention are: Through composite modification with layered double hydroxides and polydopamine, the material possesses both the anion exchange capacity of layered double hydroxides and the cationic chelation function of organic polymers, enabling simultaneous and efficient fixation of anionic heavy metals such as Cr(VI) and cationic heavy metals such as Pb(II) in the soil, thus achieving long-term fixation of multiple types of heavy metals in the soil.

[0019] By introducing silane bridging and hyperbranched polyethyleneimine to construct a three-dimensional network structure, the shielding effect of traditional polydopamine dense coating on the active sites of layered double hydroxides is effectively avoided, ensuring unobstructed anion transport channels, enhancing the structural stability of the material and its long-term immobilization capacity of heavy metals, and meeting the long-term needs for safe utilization in soil. Attached Figure Description

[0020] Figure 1 This is a SEM image of the surface of the soil conditioner prepared according to the present invention. Detailed Implementation

[0021] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0022] Example 1: A method for preparing a soil conditioner, comprising the following steps: Step 1: Weigh 50.0g of raw diatomaceous earth and place it in a beaker. Add 250mL of 4M hydrochloric acid solution to the beaker in a fume hood. Place the beaker in an 85℃ constant temperature water bath and magnetically stir continuously at 450 rpm for 55 minutes. After the reaction is complete, perform solid-liquid separation using a vacuum filtration device. Wash the solid product repeatedly with plenty of deionized water until the filtrate is neutral. Dry it in an 85℃ forced-air drying oven for 6 hours. After drying, thoroughly grind it in a mortar and pestle to obtain purified diatomaceous earth.

[0023] Step 2: Dissolve 5.0 g magnesium chloride hexahydrate, 3.2 g aluminum chloride hexahydrate, and 1.8 g urea in 150 mL of deionized water and stir until completely clear. Weigh 8.0 g purified diatomaceous earth and add it to the above solution. Sonicate for 20 min to ensure thorough dispersion, then transfer to a polytetrafluoroethylene-lined high-pressure reactor. Seal the reactor and place it in a 120°C drying oven for 19 h. After the reaction, allow it to cool naturally to room temperature. Collect the white solid product by filtration and wash it three times with hot deionized water at 60°C. Finally, dry the product at 80°C for 10 h to obtain a layered double hydroxide-diatomaceous earth composite material.

[0024] Step 3: Add 0.85g of epoxy-based silane coupling agent KH-560 to a mixed solution consisting of 75 mL of anhydrous ethanol and 25 mL of deionized water. Adjust the pH to 5 with acetic acid and hydrolyze at 60℃ for 4 hours to obtain a hydrolysate. Add 5.0g of layered double hydroxide-diatomaceous earth composite material to the hydrolysate and stir at 80℃ for 10 hours. After the reaction, centrifuge to separate the solid, wash three times with an ethanol-water mixture, and vacuum dry at 60℃ to obtain the epoxy-functionalized composite material. Then, dissolve 2.5g of polyethyleneimine in 100mL of deionized water to prepare a solution. Add the 5.0g of the epoxy-functionalized composite material obtained above to this solution and stir at 80℃ for 20 hours. After the reaction, centrifuge to separate the solid, wash three times with deionized water, and finally vacuum dry at 60℃ to obtain the modified layered double hydroxide-diatomaceous earth composite material.

[0025] Prepare 300 mL of a 10 mM Tris-HCl buffer solution with a pH of 8.5. Weigh 5.0 g of the modified layered double hydroxide-diatomaceous earth composite material and disperse it in the buffer solution. In an open system, magnetically stir at 500 rpm and add 0.5 g of dopamine hydrochloride. Maintain the reaction temperature at 32 °C and continue stirring for 9.5 h. After the reaction is complete, filter the mixture and wash the solid product with deionized water until the filtrate is colorless and transparent. Then, dry the filtrate in a vacuum drying oven at 60 °C for 8 h to obtain the soil conditioner.

[0026] Example 2: A method for preparing a soil conditioner, comprising the following steps: Step 1: Weigh 50.0g of raw diatomaceous earth and place it in a beaker. Add 250mL of 3M hydrochloric acid solution to the beaker in a fume hood. Place the beaker in an 85℃ constant temperature water bath and magnetically stir continuously at 450 rpm for 45 minutes. After the reaction is complete, use a vacuum filtration device to separate the solid and liquid phases. Wash the solid product repeatedly with plenty of deionized water until the filtrate is neutral. Dry it in an 85℃ forced-air drying oven for 6 hours. After drying, grind it thoroughly in a mortar and pestle to obtain purified diatomaceous earth.

[0027] Step 2: Dissolve 5.0 g magnesium chloride hexahydrate, 2.8 g aluminum chloride hexahydrate, and 1.2 g urea in 150 mL of deionized water and stir until completely clear. Weigh 8.0 g of purified diatomaceous earth and add it to the above solution. Sonicate for 20 min to ensure thorough dispersion, then transfer to a polytetrafluoroethylene-lined high-pressure reactor. Seal the reactor and place it in a 120°C drying oven for 16 h. After the reaction, allow it to cool naturally to room temperature. Collect the white solid product by filtration and wash it three times with hot deionized water at 60°C. Finally, dry the product at 80°C for 10 h to obtain a layered double hydroxide-diatomaceous earth composite material.

[0028] Step 3: Add 0.5g of epoxy-based silane coupling agent KH-560 to a mixed solution consisting of 75 mL of anhydrous ethanol and 25 mL of deionized water. Adjust the pH to 5 with acetic acid and hydrolyze at 60℃ for 4 hours to obtain a hydrolysate. Add 5.0g of layered double hydroxide-diatomaceous earth composite material to the hydrolysate and react at 80℃ for 10 hours. After the reaction, centrifuge to separate the solid, wash three times with an ethanol-water mixture, and vacuum dry at 60℃ to obtain the epoxy-functionalized composite material. Then, dissolve 1.8g of polyethyleneimine in 100mL of deionized water to prepare a solution. Add the 5.0g of the epoxy-functionalized composite material obtained above to this solution and react at 80℃ for 20 hours. After the reaction, centrifuge to separate the solid, wash three times with deionized water, and finally vacuum dry at 60℃ to obtain the modified layered double hydroxide-diatomaceous earth composite material.

[0029] Prepare 300 mL of a 10 mM Tris-HCl buffer solution with a pH of 8.5. Weigh 5.0 g of the modified layered double hydroxide-diatomaceous earth composite material and disperse it in the buffer solution. In an open system, magnetically stir at 500 rpm and add 0.5 g of dopamine hydrochloride. Maintain the reaction temperature at 32 °C and continue stirring for 8.5 h. After the reaction is complete, filter the mixture and wash the solid product with deionized water until the filtrate is colorless and transparent. Then, dry the filtrate in a vacuum drying oven at 60 °C for 8 h to obtain the soil conditioner.

[0030] Example 3: A method for preparing a soil conditioner, comprising the following steps: Step 1: Weigh 50.0g of raw diatomaceous earth and place it in a beaker. Add 250mL of 3.5M hydrochloric acid solution to the beaker in a fume hood. Place the beaker in an 85℃ constant temperature water bath and magnetically stir at 450 rpm for 50 minutes. After the reaction, separate the solid and liquid phases using a vacuum filtration device. Wash the solid product repeatedly with plenty of deionized water until the filtrate is neutral. Dry the filtrate in an 85℃ forced-air drying oven for 6 hours. After drying, thoroughly grind the diatomaceous earth in a mortar and pestle to obtain purified diatomaceous earth.

[0031] Step 2: Dissolve 5.0 g magnesium chloride hexahydrate, 3.0 g aluminum chloride hexahydrate, and 1.5 g urea in 150 mL of deionized water and stir until completely clear. Weigh 8.0 g of purified diatomaceous earth and add it to the above solution. Sonicate for 20 min to ensure thorough dispersion, then transfer to a polytetrafluoroethylene-lined high-pressure reactor. Seal the reactor and place it in a 120°C drying oven for 18 h. After the reaction, allow it to cool naturally to room temperature. Collect the white solid product by filtration and wash it three times with hot deionized water at 60°C. Finally, dry the product at 80°C for 10 h to obtain a layered double hydroxide-diatomaceous earth composite material.

[0032] Step 3: Add 0.5g of epoxy-based silane coupling agent KH-560 to a mixed solution consisting of 75 mL of anhydrous ethanol and 25 mL of deionized water. Adjust the pH to 5 with acetic acid and hydrolyze at 60℃ for 4 hours to obtain a hydrolysate. Add 5.0g of layered double hydroxide-diatomaceous earth composite material to the hydrolysate and react at 80℃ for 10 hours. After the reaction, centrifuge to separate the solid, wash three times with an ethanol-water mixture, and vacuum dry at 60℃ to obtain the epoxy-functionalized composite material. Then, dissolve 2.0g of polyethyleneimine in 100mL of deionized water to prepare a solution. Add the 5.0g of the epoxy-functionalized composite material obtained above to this solution and react at 80℃ for 20 hours. After the reaction, centrifuge to separate the solid, wash three times with deionized water, and finally vacuum dry at 60℃ to obtain the modified layered double hydroxide-diatomaceous earth composite material.

[0033] Prepare 300 mL of a 10 mM Tris-HCl buffer solution with a pH of 8.5. Weigh 5.0 g of the modified layered double hydroxide-diatomaceous earth composite material and disperse it in the buffer solution. In an open system, magnetically stir at 500 rpm and add 0.5 g of dopamine hydrochloride. Maintain the reaction temperature at 32 °C and continue stirring for 9 h. After the reaction is complete, filter the mixture and wash the solid product with deionized water until the filtrate is colorless and transparent. Then, dry the filtrate in a vacuum drying oven at 60 °C for 8 h to obtain the soil conditioner.

[0034] Example 4: A method for preparing a soil conditioner, comprising the following steps: Step 1: Weigh 50.0g of raw diatomaceous earth and place it in a beaker. Add 250mL of 5M hydrochloric acid solution to the beaker in a fume hood. Place the beaker in a 90℃ constant temperature water bath and magnetically stir continuously at 450 rpm for 60 minutes. After the reaction is complete, use a vacuum filtration device to separate the solid and liquid phases. Wash the solid product repeatedly with plenty of deionized water until the filtrate is neutral. Dry it in an 85℃ forced-air drying oven for 6 hours. After drying, grind it thoroughly in a mortar and pestle to obtain purified diatomaceous earth.

[0035] Step 2: Dissolve 5.0 g magnesium chloride hexahydrate, 3.5 g aluminum chloride hexahydrate, and 2 g urea in 150 mL of deionized water and stir until completely clear. Weigh 8.0 g of purified diatomaceous earth and add it to the above solution. Sonicate for 20 min to ensure thorough dispersion, then transfer to a polytetrafluoroethylene-lined high-pressure reactor. Seal the reactor and place it in a 120°C drying oven for 20 h. After the reaction, allow it to cool naturally to room temperature. Collect the white solid product by filtration and wash it three times with hot deionized water at 60°C. Finally, dry the product at 80°C for 10 h to obtain a layered double hydroxide-diatomaceous earth composite material.

[0036] Step 3: Add 1.0 g of epoxy silane coupling agent KH-560 to a mixed solution consisting of 75 mL of anhydrous ethanol and 25 mL of deionized water. Adjust the pH to 5 with acetic acid and hydrolyze at 60 °C for 4 h to obtain a hydrolysate. Add 5.0 g of layered double hydroxide-diatomaceous earth composite material to the hydrolysate and react at 80 °C for 10 h. After the reaction, centrifuge to separate the solid, wash three times with an ethanol-water mixture, and vacuum dry at 60 °C to obtain an epoxy-functionalized composite material. Then, dissolve 3.0 g of polyethyleneimine in 100 mL of deionized water to prepare a solution. Add the 5.0 g of the epoxy-functionalized composite material obtained above to this solution and react at 80 °C for 20 h. After the reaction, centrifuge to separate the solid, wash three times with deionized water, and finally vacuum dry at 60 °C to obtain the modified layered double hydroxide-diatomaceous earth composite material.

[0037] Prepare 300 mL of a 10 mM Tris-HCl buffer solution with a pH of 8.5. Weigh 5.0 g of the modified layered double hydroxide-diatomaceous earth composite material and disperse it in the buffer solution. In an open system, magnetically stir at 500 rpm and add 0.5 g of dopamine hydrochloride. Maintain the reaction temperature at 35 °C and continue stirring for 10 h. After the reaction is complete, filter the mixture and wash the solid product with deionized water until the filtrate is colorless and transparent. Then, dry the filtrate in a vacuum drying oven at 60 °C for 8 h to obtain the soil conditioner.

[0038] Example 5: A method for preparing a soil conditioner, comprising the following steps: Step 1: Weigh 50.0g of raw diatomaceous earth and place it in a beaker. Add 250mL of 2M hydrochloric acid solution to the beaker in a fume hood. Place the beaker in an 80℃ constant temperature water bath and magnetically stir continuously at 450 rpm for 40 minutes. After the reaction is complete, perform solid-liquid separation using a vacuum filtration device. Wash the solid product repeatedly with plenty of deionized water until the filtrate is neutral. Dry it in an 85℃ forced-air drying oven for 6 hours. After drying, thoroughly grind it in a mortar and pestle to obtain purified diatomaceous earth.

[0039] Step 2: Dissolve 5.0 g magnesium chloride hexahydrate, 2.5 g aluminum chloride hexahydrate, and 1 g urea in 150 mL of deionized water and stir until completely clear. Weigh 8.0 g of purified diatomaceous earth and add it to the above solution. Sonicate for 20 min to ensure thorough dispersion, then transfer to a polytetrafluoroethylene-lined high-pressure reactor. Seal the reactor and place it in a 120°C drying oven for 15 h. After the reaction, allow it to cool naturally to room temperature. Collect the white solid product by filtration and wash it three times with hot deionized water at 60°C. Finally, dry the product at 80°C for 10 h to obtain a layered double hydroxide-diatomaceous earth composite material.

[0040] Step 3: Add 0.25g of epoxy-based silane coupling agent KH-560 to a mixed solution consisting of 75 mL of anhydrous ethanol and 25 mL of deionized water. Adjust the pH to 5 with acetic acid and hydrolyze at 60℃ for 4 hours to obtain a hydrolysate. Add 5.0g of layered double hydroxide-diatomaceous earth composite material to the hydrolysate and react at 80℃ for 10 hours. After the reaction, centrifuge to separate the solid, wash three times with an ethanol-water mixture, and vacuum dry at 60℃ to obtain the epoxy-functionalized composite material. Then, dissolve 1.5g of polyethyleneimine in 100mL of deionized water to prepare a solution. Add the 5.0g of the epoxy-functionalized composite material obtained above to this solution and react at 80℃ for 20 hours. After the reaction, centrifuge to separate the solid, wash three times with deionized water, and finally vacuum dry at 60℃ to obtain the modified layered double hydroxide-diatomaceous earth composite material.

[0041] Prepare 300 mL of a 10 mM Tris-HCl buffer solution with a pH of 8.5. Weigh 5.0 g of the modified layered double hydroxide-diatomaceous earth composite material and disperse it in the buffer solution. In an open system, magnetically stir at 500 rpm and add 0.5 g of dopamine hydrochloride. Maintain the reaction temperature at 30 °C and continue stirring for 8 h. After the reaction is complete, filter the mixture and wash the solid product with deionized water until the filtrate is colorless and transparent. Then, dry the filtrate in a vacuum drying oven at 60 °C for 8 h to obtain the soil conditioner.

[0042] Comparative Example 1: The difference between Comparative Example 1 and Example 1 is that ordinary diatomaceous earth is used as a soil conditioner.

[0043] Comparative Example 2: The difference between Comparative Example 2 and Example 1 is that step 2 is omitted in the preparation process of the soil conditioner, that is, the diatomaceous earth surface does not bind layered double hydroxides.

[0044] Comparative Example 3: The difference between Comparative Example 3 and Example 1 is that step 3 is omitted in the preparation of the soil conditioner, that is, the layered double hydroxide-diatomite composite material does not bind polydopamine.

[0045] Comparative Example 4: The difference between Comparative Example 4 and Example 1 is that the layered double hydroxide-diatomite composite material in step 3 of the soil conditioner preparation process was not modified.

[0046] Performance testing: 1. Heavy metal adsorption capacity test: Pb(NO3)2 and K2Cr2O7 were selected to prepare Pb adsorption capacity tests with initial concentrations of 50–500 mg / L. 2+ Cr 6+ The simulated contaminated solution was adjusted to pH neutral (within the common soil pH range). 0.1 g of the test amendment (Examples 1-5 and Comparative Examples 1-4) was weighed and added to 50 mL of the simulated solution. The mixture was then placed in a 30°C water bath shaker (150 rpm) for 24 h until adsorption equilibrium was reached. After the reaction, the mixture was filtered through a 0.45 μm microporous membrane and analyzed using an atomic absorption spectrophotometer (Pb). 2+ ) and diphenylcarbazide spectrophotometry (Cr 6+ ) Determine the concentration of residual heavy metals in the filtrate and calculate the adsorption capacity using the formula: Q = (C o -C e )×V / m (Q is the adsorption capacity, in mg / g; C o For the initial concentration, C e (Equilibrium concentration, unit: mg / L; V: solution volume, unit: L; m: modifier mass, unit: g). Test results are shown in Table 1.

[0047] 2. Long-term stability test of heavy metals: The soil column leaching method was used to apply the amendment to the soil contaminated with heavy metals (Pb). 2+ Content 500mg / kg, Cr 6+ A mixture of soil (containing 300 mg / kg) at a mass ratio of 1:20 was thoroughly mixed and packed into plexiglass columns (5 cm inner diameter, 30 cm high, with a 2 cm layer of quartz sand at the bottom), with each column containing 100 g of soil. The mixture was leached weekly with 50 mL of deionized water (simulating natural rainfall) from top to bottom, and the leachate was collected and monitored continuously for 12 weeks. The Pb content in the leachate was determined using the same detection method described above. 2+ Cr 6+ Concentration was determined, and the cumulative leaching amount over 12 weeks was calculated to assess long-term stability (lower cumulative leaching amount indicates stronger stability). Test results are shown in Table 1.

[0048] Table 1:

[0049] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a soil conditioner, characterized in that, Includes the following steps: S1. Mix diatomaceous earth with hydrochloric acid solution, heat and stir to react. After the reaction is complete, filter and wash with deionized water until the filtrate is neutral. Then dry and grind to obtain purified diatomaceous earth. S2. Dissolve magnesium chloride hexahydrate, aluminum chloride hexahydrate and urea in deionized water to form a salt-urea mixed solution. Then add purified diatomaceous earth and disperse it. Then carry out a hydrothermal reaction of the suspension. After the reaction is completed, cool naturally and filter. Wash the solid product with hot deionized water and dry to obtain a layered double hydroxide-diatomaceous earth composite material. S3. The layered double hydroxide-diatomaceous earth composite material was dispersed in Tris-HCl buffer solution, and dopamine hydrochloride was added under stirring to carry out the reaction. After the reaction was completed, the mixture was filtered, the solid product was washed with deionized water and dried to obtain the soil conditioner.

2. The method for preparing a soil conditioner according to claim 1, characterized in that, In step S1, the concentration of the hydrochloric acid solution is 2–5 mol / L.

3. The method for preparing a soil conditioner according to claim 1, characterized in that, In step S1, the heating temperature is 80–90°C and the reaction time is 40–60 min.

4. The method for preparing a soil conditioner according to claim 1, characterized in that, In step S2, the mass ratio of magnesium chloride hexahydrate, aluminum chloride hexahydrate, and urea is 10:5-7:2-4.

5. The method for preparing a soil conditioner according to claim 1, characterized in that, In step S2, the hydrothermal reaction time is 15–20 h.

6. The method for preparing a soil conditioner according to claim 1, characterized in that, In step S3, the layered double hydroxide-diatomite composite material undergoes modification treatment, including the following steps: S31. Add the epoxy silane coupling agent to a mixed solution of ethanol and water, heat and stir to hydrolyze, and obtain the hydrolysate; S32. The layered double hydroxide-diatomite composite material is added to the hydrolysate, heated and stirred to react, and then centrifuged, washed and dried to obtain the epoxy-based layered double hydroxide-diatomite composite material. S33. Polyethyleneimine is added to deionized water and stirred to dissolve, thus obtaining a polyethyleneimine solution. Epoxy-based layered double hydroxide-diatomaceous earth composite material is added to the polyethyleneimine solution, heated and stirred to react, and then centrifuged, washed, and dried to obtain the final product.

7. The method for preparing a soil conditioner according to claim 6, characterized in that, In step S32, the mass ratio of the layered double hydroxide-diatomaceous earth composite material to the epoxy silane coupling agent is 10:0.5-2.

8. The method for preparing a soil conditioner according to claim 6, characterized in that, In step S33, the mass ratio of the epoxy-layered double hydroxide-diatomite composite material to polyethyleneimine is 10:3 to 6.

9. The method for preparing a soil conditioner according to claim 1, characterized in that, In step S3, the reaction temperature is 30-35℃ and the reaction time is 8-10h.

10. A soil conditioner, characterized in that, It is prepared by the method described in any one of claims 1 to 9.

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