Potassium sulfate functional fertilizer for repairing heavy metals in soil and preparation method thereof

Abstract

The invention discloses a kind of potassium sulfate functional fertilizer for repairing soil heavy metals and its preparation method, belong to the technical field of agricultural fertilizers;By weight parts, it is composed as follows, including:40 60 parts of potassium sulfate, 5 15 parts of homemade graphene oxide bentonite composite material, 15 35 parts of modified walnut biochar, 3 8 parts of lignin sulfonate, 1 3 parts of kaolin.The application adopts walnut biochar, and by pyrolysis activation, makes the biochar prepared, with developed micropore and mesoporous structure, can provide huge physical adsorption space;And the application introduces mercaptopropylmethyldimethoxysilane modified biochar, the sulfhydryl group therein as soft base, for the soft acid adsorption of heavy metals such as heavy metal elements cadmium, lead, mercury, and is strong, and is basically not absorbed for the potash fertilizer in potassium sulfate fertilizer, can be selective, powerful capture target heavy metal ions, and does not adsorb potash fertilizer, so that potassium sulfate fertilizer can be efficiently utilized.

Description

Technical Field

[0001] The present invention belongs to the technical field of agricultural fertilizers, and specifically relates to a potassium sulfate functional fertilizer for repairing heavy metals in soil and a preparation method thereof. Background Art

[0002] Heavy metals are the most common type of environmental pollutant, and soil is the ultimate destination for various heavy metal pollution sources, including the atmosphere, water, and agricultural production. Because soil is an extremely complex system with three phases, solid, liquid, and gas, soil pollution is less easily detected than air and water pollution. The hidden nature of heavy metal pollution in soil, the long-term cumulative damage, and the irreversible nature of its effects make remediation of heavy metal-contaminated soil a very difficult and challenging task.

[0003] In fact, heavy metal pollution in soil involves many aspects of industry, agriculture, human production and life. On the one hand, heavy metals may diffuse into the soil at various stages, starting from ore mining and becoming components of industrial products or finished products; on the other hand, agricultural production activities such as the use of sewage irrigation, application of chemical fertilizers, urban garbage, sludge and pesticides also increase the pollution load of heavy metals in the soil environment.

[0004] The existing technology for repairing heavy metals in soil includes the Chinese invention patent with application number: CN201910383541.X, which discloses a multi-functional corn straw biochar compound fertilizer for repairing cadmium pollution in soil and a preparation method thereof, characterized in that it is made of the following raw materials in parts by weight: 10 parts of compound fertilizer raw material and 1 part of kaolin; the compound fertilizer raw material is made of the following raw materials in parts by weight: 4 parts of composite biochar material and 1 part of urea; the composite biochar material is made of the following raw materials in parts by weight: 5-10 parts of corn straw, 1 part of heavy superphosphate and 1 part of diatomaceous earth; the preparation method of the multi-functional corn straw biochar compound fertilizer comprises the following steps: Step 1: drying the corn straw and crushing it; Step 2: mixing the corn straw, heavy superphosphate and diatomaceous earth in proportion to obtain a mixed powder; Step 3: placing the mixed powder in a tubular furnace for high-temperature pyrolysis, the pyrolysis temperature is 300-600°C, and the pyrolysis time is 1 hour to obtain a composite biochar material.

[0005] The above-mentioned existing technology uses a composite biochar material prepared from corn straw, heavy superphosphate, and diatomaceous earth. Although it has a better passivation effect on cadmium in the soil, the above-mentioned biochar material will also enhance the adsorption of other cations such as potassium ions, which will greatly sacrifice the effectiveness of potassium fertilizers. In addition, the ash content of corn straw biochar is high, and the effective carbon skeleton content per unit mass of biochar is low. In addition, the high ash content may reduce the specific surface area and pore volume of the biochar, greatly limiting its physical adsorption capacity.

[0006] The prior art includes a Chinese invention patent with application number: CN202210803533.8, which discloses a method for preparing a slow-release compound fertilizer that prevents heavy metal absorption. Through the steps of heavy metal adsorbent preparation, compound fertilizer batching, granulation and coating treatment, mixing and the like, a slow-release compound fertilizer granule with amino silica gel as a heavy metal adsorbent, calcium alginate as a coating agent, and an inner core containing nitrogen, phosphorus, potassium, magnesium and organic complex nutrients is prepared. The slow-release compound fertilizer that prevents heavy metal absorption is a mixture of the two. The amino silica gel utilizes a large number of pores and surface functional groups on its surface to effectively adsorb common heavy metal ions, while the slow-release compound fertilizer particles are separated from the heavy metal adsorbent. In this way, when watering crops, the heavy metal adsorbent will first adsorb a large amount of heavy metal ions in the soil, and then the components of the inner core of the compound fertilizer will be slowly released into the soil and then absorbed by the crops. Since heavy metal ions have already been adsorbed by amino silica gel in large quantities, the amount of heavy metals absorbed by crops during the long growth cycle is greatly reduced, and the heavy metal ions occupy the active sites of amino silica gel in advance, and beneficial cations such as potassium, calcium, magnesium, etc. will be absorbed slowly and calmly by crops.

[0007] The above-mentioned existing technology uses a simple physical mixture of slow-release compound fertilizer particles and heavy metal adsorbents. However, in actual use, due to the influence of water migration in the soil and the complex ion diffusion paths, this simple physical mixture of the above-mentioned existing technology cannot guarantee that the heavy metal adsorbent can timely and effectively capture heavy metals before they reach the crop root system, nor can it prevent potassium ions and other ions released by the slow-release compound fertilizer particles from contacting and being adsorbed by the adsorbent. This spatial and temporal uncertainty makes the above-mentioned existing technology unstable in its heavy metal control effect.

[0008] Therefore, in order to solve the above technical problems, the present application provides a potassium sulfate functional fertilizer for repairing heavy metals in soil and a preparation method thereof. Summary of the Invention

[0009] To address the deficiencies in the above-mentioned technical solutions, the present invention aims to provide a potassium sulfate functional fertilizer for remediating heavy metals in soil and a method for preparing the same. The present invention can achieve this objective through the following technical solution: A potassium sulfate functional fertilizer for remediating heavy metals in soil, comprising, by weight, 40-60 parts potassium sulfate, 5-15 parts self-made graphene oxide bentonite composite material, 15-35 parts modified walnut biochar, 3-8 parts lignin sulfonate, and 1-3 parts kaolin.

[0010] The method for preparing a homemade graphene oxide-bentonite composite material comprises the following steps: ultrasonically dispersing modified graphene oxide in deionized water to obtain a modified graphene oxide suspension; ultrasonically dispersing bentonite in deionized water to obtain a bentonite suspension; mixing the two suspensions and transferring them to a three-necked flask, introducing and maintaining a nitrogen atmosphere; slowly adding a NaOH solution dropwise to adjust the pH of the mixed suspension to 9; heating the reaction system to 65 degrees Celsius, and dropwise adding 10 ml of an (NH4)2S2O8 aqueous solution, and then dropwise adding 10 ml of a NaHSO4 aqueous solution after 15 minutes; continuing to stir and react for 4 hours; naturally cooling to room temperature, and collecting the product by filtration; washing the solid product with deionized water until the filtrate is neutral; washing once with ethanol, and finally drying in a vacuum oven at 60 degrees Celsius for 12 hours to constant weight, and grinding into powder, thereby preparing the homemade graphene oxide-bentonite composite material.

[0011] The concentration of the NaOH solution is 0.5 mol / L.

[0012] The modified graphene oxide is prepared by a method comprising the following steps: taking 1 g of graphene oxide and placing it in 500 mL of N,N-dimethylformamide, ultrasonically treating it for 30 minutes to obtain a uniformly dispersed graphene oxide dispersion; then introducing nitrogen for 30 minutes to create an inert environment; taking another container, adding 0.5 g of cysteamine hydrochloride and 0.5 g of 2,2'-azobisisobutyronitrile to 250 mL of N,N-dimethylformamide, and ultrasonically treating it for 30 minutes to prepare a mixed solution; adding the mixed solution to the dispersion; continuing to introduce nitrogen for 30 minutes; sealing the reaction mixture and placing it in an oil bath at 70°C, heating and stirring it for 12 hours; after the reaction is completed, cooling it to room temperature; collecting the product by centrifugation, and washing it thoroughly with a mixed solvent of n-hexane and ethyl acetate, ethanol, and distilled water for 3-5 times in sequence; and finally freeze-drying the washed product to prepare the modified graphene oxide.

[0013] Furthermore, the CAS number of the cysteamine hydrochloride is: 156-57-0;

[0014] Furthermore, the volume ratio of the mixed solvent of n-hexane and ethyl acetate is 1:1;

[0015] The biochar pretreatment comprises the following steps: crushing walnut shells, grinding them into powder, passing them through a 100-mesh sieve, and washing them with deionized water until the supernatant is clear; then placing the washed walnut shell powder in an 80-degree Celsius oven and drying it at a constant temperature for 12 hours, thereby completing the pretreatment of the walnut shell powder; placing the pretreated walnut shell powder in a crucible, placing it in a muffle furnace, and introducing nitrogen to maintain an inert environment; setting the heating rate of the muffle furnace to 10°C / min, and after reaching 900°C, continuing pyrolysis for 180 minutes to obtain walnut shell biochar; taking it out after the temperature naturally drops to room temperature, washing it with deionized water, and drying it in an 80-degree Celsius oven to obtain walnut biochar.

[0016] The modified walnut biochar preparation method comprises the following steps: adding anhydrous ethanol and deionized water to a flask; magnetically stirring and adjusting the solution pH to 11 with 1 mol / L sodium hydroxide; weighing 6 g of mercaptopropylmethyldimethoxysilane, slowly adding the mixture to the mixed solution, and continuing to stir for 30 minutes; subsequently placing the mixed solution under a nitrogen-protected atmosphere, adding the walnut biochar to the reaction solution, placing the reaction vessel in an oil bath, heating the mixture to 85 degrees Celsius, and maintaining a reflux reaction for 12 hours; after the reaction is completed, stopping heating, and naturally cooling the mixture to room temperature under a nitrogen atmosphere; collecting the reaction product by suction filtration, washing the reaction product with anhydrous ethanol to remove unreacted substances, and finally drying the reaction product in a 60-degree vacuum oven, and grinding the reaction product to 60 mesh, thereby preparing the modified walnut biochar.

[0017] A method for preparing a potassium sulfate functional fertilizer for repairing heavy metals in soil comprises the following steps: weighing potassium sulfate, a homemade graphene oxide bentonite composite material, modified walnut biochar, and kaolin, adding the mixture to a mixing and stirring device, starting the mixing device and stirring at 300 r / min for 20 minutes; adding lignin sulfonate to deionized water, stirring and dissolving the mixture to prepare a binder solution with a concentration of 15%; then transferring the evenly mixed dry material to a disc granulator, starting the granulator, and slowly and evenly spraying the binder solution onto the powder tumbling in the disc granulator, controlling the spraying amount and speed so that the particles gradually grow, and forming a potassium sulfate functional fertilizer with a diameter between 2 and 5 mm; finally, evenly spreading the prepared potassium sulfate functional fertilizer on a drying tray, placing the tray in a forced air drying oven, and drying the particles at 70 degrees Celsius to a constant weight; thus, potassium sulfate functional fertilizer with a diameter of 2 to 5 mm is prepared.

[0018] Furthermore, a potassium sulfate functional fertilizer for repairing heavy metals in soil comprises, by weight, 50 parts of potassium sulfate, 10 parts of homemade graphene oxide bentonite composite material, 25 parts of modified walnut biochar, 5 parts of lignin sulfonate, and 2 parts of kaolin.

[0019] Furthermore, the content of K2O in the potassium sulfate is 50-54%.

[0020] Furthermore, the lignin sulfonate is sodium lignin sulfonate.

[0021] The present invention has the beneficial effects:

[0022] 1. This application uses walnut biochar and activates it through high-temperature cracking, so that the prepared biochar has a developed microporous and mesoporous structure, which can provide a huge physical adsorption space; and this application introduces mercaptopropylmethyldimethoxysilane to modify the biochar. The mercapto group in the biochar acts as a soft base, which has strong adsorption properties for soft acids of heavy metals such as cadmium, lead, and mercury, but basically does not absorb potassium fertilizer in potassium sulfate fertilizer. It can selectively and strongly capture target heavy metal ions without adsorbing potassium fertilizer, so that potassium sulfate fertilizer can be efficiently utilized;

[0023] 2. The homemade graphene oxide-bentonite composite material of the present application, wherein the homemade graphene oxide is a nitrogen-containing chelating ligand with more adsorption sites, and an initiator is used to effectively graft the homemade graphene oxide onto the bentonite surface, firmly binding the homemade graphene oxide to the bentonite carrier and forming a stable three-dimensional network structure, making it less likely to dissociate in the soil environment; and the physical adsorption capacity brought by the layered structure of the homemade graphene oxide, through grafting the composite bentonite, allows these sites to be effectively exposed, which can complete the adsorption of more heavy metals;

[0024] 3. This application can improve the graphitization degree of walnut biochar through high-temperature treatment, thereby enhancing the π-electron system, and the homemade graphene oxide bentonite composite material in the component also contains a π-electron system. When the two are used in combination, the composite π-electron interface formed can provide stronger adsorption sites. The electronic synergistic effect generated by the coupling of the π-electron system makes the potassium sulfate functional fertilizer exhibit better adsorption performance than a single component. DETAILED DESCRIPTION

[0025] To make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with Examples. The illustrative embodiments of the present invention and their description are only used to explain the present invention and are not intended to limit the present invention. In addition, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each smaller range between the intermediate value within any stated value or stated range and any other stated value or intermediate value within the range is also included in the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0026] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0027] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the description of the invention. The description and examples are intended to be exemplary only.

[0028] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0029] The "parts" indicated in the following examples are all parts by weight.

[0030] Example 1

[0031] A potassium sulfate functional fertilizer for repairing heavy metals in soil comprises: 40 parts of potassium sulfate, 5 parts of homemade graphene oxide bentonite composite material, 15 parts of modified walnut biochar, 3 parts of sodium lignin sulfonate, and 1 part of kaolin;

[0032] The kaolin was purchased from Guangzhou Zhanfei Chemical Technology Co., Ltd.

[0033] The graphene oxide was purchased from Shanghai Naio Nano Technology Co., Ltd.

[0034] The modified graphene oxide was prepared by a method comprising the following steps: 1 g of graphene oxide was placed in 500 mL of N,N-dimethylformamide and ultrasonically treated for 30 minutes to obtain a uniformly dispersed graphene oxide dispersion; nitrogen was then introduced for 30 minutes to create an inert environment; in another container, 0.5 g of cysteamine hydrochloride and 0.5 g of 2,2'-azobisisobutyronitrile (initiator) were added to 250 mL of N,N-dimethylformamide and ultrasonically treated for 30 minutes to prepare a mixed solution; the solution containing cysteamine hydrochloride and 2,2'-azobisisobutyronitrile was heated to 40 ℃ and then heated to 30 ℃ for 2 hours. A mixed solution of 2'-azobisisobutyronitrile and N,N-dimethylformamide was added to the graphene oxide dispersion; nitrogen was then continued to be introduced for 30 minutes; the reaction mixture was transferred to a round-bottom flask with a magnetic stirrer, sealed, and heated in an oil bath at 70°C with stirring for 12 hours; after the reaction was completed, the product was cooled to room temperature; the product was then collected by centrifugal filtration and washed thoroughly 3-5 times with a mixed solvent of n-hexane and ethyl acetate, ethanol, and distilled water; and finally, the washed product was freeze-dried to prepare modified graphene oxide.

[0035] The CAS number of the cysteamine hydrochloride is: 156-57-0;

[0036] The volume ratio of the mixed solvent of n-hexane and ethyl acetate is 1:1;

[0037] Preparation method of homemade graphene oxide bentonite composite material: 1g modified graphene oxide was ultrasonically dispersed in 400mL deionized water for 1 hour to obtain a modified graphene oxide suspension; then 3g bentonite was ultrasonically dispersed in 200mL water for 30min to obtain a uniform bentonite suspension; the modified graphene oxide suspension was mixed with the bentonite suspension and transferred to a three-necked flask with magnetic stirring, nitrogen was introduced for 30min to remove dissolved oxygen, and the nitrogen atmosphere was maintained; 0.5mol / L NaOH solution was slowly added dropwise to adjust the pH of the mixed suspension to 9; the reaction system was heated to 65 degrees Celsius, and 10ml of 1% concentration (NH4)2S2O8 aqueous solution was added dropwise, and 10ml of 1% concentration NaHSO4 aqueous solution was added dropwise after 15min; finally, the reaction temperature was maintained unchanged and the stirring reaction was continued for 4h; after naturally cooling to room temperature, the solid product was collected by filtration. The solid product was washed with deionized water until the filtrate was neutral; then washed once with ethanol, and finally dried in a vacuum oven at 60 degrees Celsius for 12 hours to constant weight, and ground into powder to prepare a homemade graphene oxide bentonite composite material.

[0038] The bentonite is sodium bentonite, purchased from Sichuan Hexinrunda Mining Co., Ltd.

[0039] Biochar pretreatment: The walnut shells were crushed and ground into powder, passed through a 100-mesh sieve, and washed with deionized water until the supernatant was clear; the washed walnut shell powder was then placed in an 80-degree Celsius oven and dried at a constant temperature for 12 hours to complete the pretreatment of the walnut shell powder; the pretreated walnut shell powder was placed in a crucible, placed in a muffle furnace, and nitrogen was introduced to maintain an inert environment. The heating rate of the muffle furnace was set at 10°C / min. After reaching 900°C, pyrolysis was continued for 180 minutes to obtain walnut shell biochar. The temperature was naturally reduced to room temperature and then taken out, washed with deionized water, and dried in an 80-degree Celsius oven to obtain walnut biochar.

[0040] Preparation method of modified walnut biochar: In a 500ml flask, add 100ml of anhydrous ethanol and 100ml of deionized water; start magnetic stirring with 1mol / L sodium hydroxide to adjust the pH of the solution to 11; then, weigh 6g of mercaptopropylmethyldimethoxysilane and slowly add it to the mixed solution of water and ethanol with the adjusted pH, and continue stirring for 30min; then place the mixed solution under a nitrogen protection atmosphere, add the pretreated walnut biochar to the reaction solution under nitrogen protection, place the reaction vessel in an oil bath, heat it to 85 degrees Celsius, and maintain reflux reaction for 12h; after the reaction is completed, stop heating and let the reaction system cool naturally to room temperature under a nitrogen atmosphere; then filter and collect the reaction product, then use anhydrous ethanol to wash the reaction product to remove unreacted substances, and finally place the reaction product in a 60-degree vacuum box to dry to constant weight, and grind it into 60 mesh to prepare modified walnut biochar.

[0041] A method for preparing a potassium sulfate functional fertilizer for repairing heavy metals in soil comprises the following steps: weighing potassium sulfate, a homemade graphene oxide bentonite composite material, modified walnut biochar, and kaolin, adding the mixture to a mixing and stirring device, starting the mixing device and stirring at 300 r / min for 20 minutes; adding lignin sulfonate to deionized water, stirring and dissolving the mixture to prepare a binder solution with a concentration of 15%; then transferring the evenly mixed dry material to a disc granulator, starting the granulator, and slowly and evenly spraying the binder solution onto the powder tumbling in the disc granulator, controlling the spraying amount and speed so that the particles gradually grow, and forming a potassium sulfate functional fertilizer with a diameter between 2 and 5 mm; finally, evenly spreading the prepared potassium sulfate functional fertilizer on a drying tray, placing the tray in a forced air drying oven, and drying the particles at 70 degrees Celsius to a constant weight; thus, potassium sulfate functional fertilizer with a diameter of 2 to 5 mm is prepared.

[0042] Example 2

[0043] A potassium sulfate functional fertilizer for repairing heavy metals in soil comprises: 45 parts of potassium sulfate, 8 parts of a homemade graphene oxide bentonite composite material, 20 parts of modified walnut biochar, 4 parts of sodium lignin sulfonate, and 2 parts of kaolin;

[0044] Among them, the preparation method of the homemade graphene oxide bentonite composite material, the preparation method of the modified walnut biochar, and the preparation method of the potassium sulfate functional fertilizer for repairing heavy metals in soil in Example 2 are all consistent with Example 1.

[0045] Example 3

[0046] A potassium sulfate functional fertilizer for repairing heavy metals in soil comprises: 50 parts of potassium sulfate, 10 parts of a homemade graphene oxide bentonite composite material, 25 parts of modified walnut biochar, 5 parts of sodium lignin sulfonate, and 2 parts of kaolin;

[0047] Among them, the preparation method of the homemade graphene oxide bentonite composite material, the preparation method of the modified walnut biochar, and the preparation method of the potassium sulfate functional fertilizer for repairing heavy metals in soil in Example 3 are all consistent with Example 1.

[0048] Example 4

[0049] A potassium sulfate functional fertilizer for repairing heavy metals in soil comprises: 55 parts of potassium sulfate, 12 parts of a homemade graphene oxide bentonite composite material, 30 parts of modified walnut biochar, 7 parts of sodium lignin sulfonate, and 3 parts of kaolin;

[0050] Among them, the preparation method of the homemade graphene oxide bentonite composite material, the preparation method of the modified walnut biochar, and the preparation method of the potassium sulfate functional fertilizer for repairing heavy metals in soil in Example 4 are all consistent with Example 1.

[0051] Example 5

[0052] A potassium sulfate functional fertilizer for repairing heavy metals in soil comprises: 60 parts of potassium sulfate, 15 parts of a homemade graphene oxide bentonite composite material, 35 parts of modified walnut biochar, 8 parts of sodium lignin sulfonate, and 3 parts of kaolin;

[0053] Among them, the preparation method of the homemade graphene oxide bentonite composite material, the preparation method of the modified walnut biochar, and the preparation method of the potassium sulfate functional fertilizer for repairing heavy metals in soil in Example 5 are all consistent with Example 1.

[0054] Comparative Example 1

[0055] A potassium sulfate functional fertilizer for repairing heavy metals in soil comprises: 50 parts of potassium sulfate, 5 parts of lignin sulfonate, and 37 parts of kaolin. Comparative Example 1 is based on Example 3, except that the addition of a homemade graphene oxide bentonite composite material and modified walnut biochar is omitted, and their components are replaced with kaolin of equal weight. The specific preparation method of the potassium sulfate functional fertilizer for repairing heavy metals in soil also refers to the preparation method of Example 3 to prepare the potassium sulfate functional fertilizer.

[0056] Comparative Example 2

[0057] A potassium sulfate functional fertilizer for repairing heavy metals in soil comprises: 50 parts of potassium sulfate, 10 parts of a homemade graphene oxide bentonite composite material, 5 parts of lignin sulfonate, and 27 parts of kaolin;

[0058] This comparative example 2 is based on Example 3, except that the addition of modified walnut biochar was omitted and its components were replaced with an equal weight of kaolin;

[0059] Among them, the preparation method of the homemade graphene oxide bentonite composite material and the preparation method of the potassium sulfate functional fertilizer for repairing heavy metals in soil in Comparative Example 2 are both consistent with those in Example 3.

[0060] Comparative Example 3

[0061] A potassium sulfate functional fertilizer for repairing heavy metals in soil comprises: 50 parts of potassium sulfate, 25 parts of modified walnut biochar, 5 parts of lignin sulfonate, and 12 parts of kaolin;

[0062] This comparative example 3 is based on Example 3, except that the addition of the homemade graphene oxide bentonite composite material is omitted and its components are replaced with kaolin of equal weight;

[0063] Among them, the preparation method of the modified walnut biochar in Comparative Example 3 and the preparation method of the potassium sulfate functional fertilizer for repairing heavy metals in soil are both consistent with those in Example 3.

[0064] Comparative Example 4

[0065] A potassium sulfate functional fertilizer for repairing heavy metals in soil comprises: 50 parts of potassium sulfate, 10 parts of a homemade graphene oxide bentonite composite material, 25 parts of walnut biochar, 5 parts of lignin sulfonate, and 2 parts of kaolin;

[0066] Comparative Example 4 is based on Example 3, except that the modification step of the walnut biochar was omitted and its components were replaced with an equal weight of unmodified walnut biochar;

[0067] Among them, the preparation method of the homemade graphene oxide bentonite composite material and the preparation method of the potassium sulfate functional fertilizer for repairing heavy metals in soil in Comparative Example 4 are both consistent with those in Example 3.

[0068] Comparative Example 5

[0069] A potassium sulfate functional fertilizer for repairing heavy metals in soil comprises: 50 parts of potassium sulfate, 10 parts of graphene oxide bentonite composite material, 25 parts of modified walnut biochar, 5 parts of lignin sulfonate, and 2 parts of kaolin;

[0070] This comparative example 5 is based on Example 3, except that the step of modifying the graphene oxide-bentonite composite material is omitted, and commercially available graphene oxide is directly used;

[0071] In addition, the preparation method of the modified walnut biochar and the preparation method of the potassium sulfate functional fertilizer for repairing heavy metals in soil in Comparative Example 5 are the same as those in Example 3.

[0072] Test example

[0073] Soil from the surface layer of 0-20 cm was collected from contaminated farmland around a mining area in Jiang'an County, Yibin City, Sichuan Province. The soil was naturally air-dried and then passed through a 2 mm sieve. The basic physical and chemical properties of the soil are shown in Table 1.

[0074] Table 1

[0075]

[0076] 10 kg of soil was weighed for each pot and placed in a plastic bucket with a diameter of 35 cm and a height of 40 cm. The following treatment was performed: 20 g of potassium sulfate functional fertilizer to repair heavy metals in the soil was added and corn was sown and planted. The plants were cultured in a light incubator. After 45 days, when the corn reached the seedling stage, it was harvested and soil and plant samples were taken for testing.

[0077] Table 2

[0078]

[0079] As shown in Table 2, Examples 1-5 of the present application can basically achieve an adsorption rate of more than 80% for heavy metals in the soil, and have excellent effectiveness in repairing heavy metals in the soil; the components of Comparative Example 1 include 50 parts of potassium sulfate, 5 parts of lignin sulfonate, and 37 parts of kaolin; it can also reduce the heavy metal content by a certain proportion. The possible reason is that kaolin can also play a partial adsorption role, and the planted corn may also be enriched with a part of the heavy metals, so Comparative Example 1 also shows a certain heavy metal adsorption capacity.

[0080] Comparative Example 2 omitted the addition of modified walnut biochar, and Comparative Example 3 omitted the addition of the homemade graphene oxide bentonite composite material; the adsorption effects of the two comparative examples were significantly stronger than those of Comparative Example 1, but there were significant differences in adsorption performance between them and Examples 1-5. The possible reasons are:

[0081] The modified walnut biochar in Examples 1-5 is activated by high-temperature cracking, so that the prepared biochar has a developed microporous and mesoporous structure, which can provide a huge physical adsorption space; and the present application introduces mercaptopropylmethyldimethoxysilane to modify the biochar, in which the mercapto group serves as a soft base and has strong soft acid adsorption for heavy metal elements such as cadmium, lead, and mercury; and a homemade graphene oxide bentonite composite material, in which the homemade graphene oxide is a nitrogen-containing chelating ligand with more adsorption sites, and an initiator is used to effectively graft the homemade graphene oxide on the bentonite surface, firmly binding the homemade graphene oxide to the bentonite carrier, and forming a stable three-dimensional network structure, making it less likely to dissociate in the soil environment; and the physical adsorption capacity brought by the layered structure of the homemade graphene oxide, through grafting the composite bentonite, makes these sites effectively exposed, which can complete the adsorption of more heavy metals.

[0082] In Comparative Example 4, the modification step of the walnut biochar was omitted, and its components were replaced with unmodified walnut biochar of the same weight; in Comparative Example 5, the modification step of the graphene oxide bentonite composite material was omitted; Comparative Examples 4 and 5 can also achieve the better repair effect in Comparative Examples 1-5, but cannot exceed 60%. The possible reason is that: in Examples 1-5, high temperature treatment can improve the graphitization degree of the walnut biochar, thereby enhancing the π electron system, and the homemade graphene oxide bentonite composite material in the component also contains a π electron system. When the two are used in combination, the composite π electron interface formed can provide a stronger adsorption site. The electronic synergistic effect generated by the coupling of the π electron system makes the potassium sulfate functional fertilizer exhibit better adsorption and repair performance than a single component.

[0083] Table 3

[0084]

[0085] As shown in Table 3, in Comparative Example 1, the remediation of heavy metals in the soil is the weakest, which is reflected in the plant height. This is because the high concentration of heavy metal stress in the soil has a significant inhibitory effect on the division of plant cells, making it impossible for cells to divide normally in a short period of time, causing chromosome mutations, thereby inhibiting the growth of plant seedlings; therefore, Comparative Example 1 presents the shortest plant height.

[0086] In Examples 1-5, because the prepared biochar introduced mercaptopropylmethyldimethoxysilane-modified biochar, the mercapto group in it acts as a soft base and has strong adsorption properties for soft acids of heavy metals such as cadmium, lead, and mercury; while it basically does not absorb the potash fertilizer in potassium sulfate fertilizer, it can selectively and powerfully capture the target heavy metal ions without adsorbing potassium fertilizer, so that potassium sulfate fertilizer can be efficiently utilized. Potassium can promote the cell division rate of meristems, thereby making the plant height of Examples 1-5 higher. Although Examples 4 and 5 added more potassium sulfate, the growth of the plant may also be affected by the efficiency of heavy metal removal. However, the height of the corn seedlings in Examples 1-5 is also significantly higher than that of the comparative example.

[0087] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A potassium sulfate functional fertilizer for repairing heavy metals in soil, characterized in that: The composition is as follows in parts by weight: 40-60 parts of potassium sulfate, 5-15 parts of homemade graphene oxide bentonite composite material, 15-35 parts of modified walnut biochar, 3-8 parts of lignin sulfonate, and 1-3 parts of kaolin; The self-made graphene oxide bentonite composite material is prepared by the following method: ultrasonically dispersing modified graphene oxide in deionized water to obtain a modified graphene oxide suspension; The bentonite suspension was ultrasonically dispersed in deionized water; the two suspensions were mixed and transferred to a three-necked flask, and a nitrogen atmosphere was introduced and maintained; NaOH solution was slowly added dropwise to adjust the pH of the mixed suspension to 9; the reaction system was heated to 65 degrees Celsius, and (NH4)2S2O8 and NaHSO4 aqueous solutions were added dropwise in sequence; the reaction was continued with stirring for 4 hours; after naturally cooling to room temperature, the product was collected by filtration; the solid product was washed, dried to constant weight, and ground into powder to prepare a homemade graphene oxide bentonite composite material; The modified graphene oxide is prepared by the following method: placing graphene oxide in N,N-dimethylformamide and ultrasonically treating it for 30 minutes to obtain a graphene oxide dispersion; then introducing nitrogen for 30 minutes; taking another container, adding cysteamine hydrochloride and 2,2'-azobisisobutyronitrile to N,N-dimethylformamide, and ultrasonically treating it for 30 minutes to prepare a mixed solution; adding the mixed solution to the dispersion; continuing to introduce nitrogen for 30 minutes; sealing the reaction mixture, placing it in a 70°C oil bath, heating and stirring it for 12 hours; after the reaction is completed, cooling it to room temperature; collecting the product by centrifugation, and washing it thoroughly with a mixed solvent of n-hexane and ethyl acetate, ethanol, and distilled water for 3-5 times in sequence; and finally freeze-drying the washed product to prepare the modified graphene oxide. The modified walnut biochar is prepared by the following method: adding anhydrous ethanol and deionized water to a flask; magnetically stirring and adjusting the pH of the solution to 11 with sodium hydroxide; taking mercaptopropylmethyldimethoxysilane, adding it to the mixed solution, and continuing to stir for 30 minutes; then placing the mixed solution under a nitrogen protection atmosphere, adding the walnut biochar to the reaction solution, and placing the reaction container in an oil bath, heating it to 85 degrees Celsius, and maintaining reflux reaction for 12 hours; after the reaction is completed, stopping heating and naturally cooling to room temperature under a nitrogen atmosphere; collecting the reaction product by suction filtration, and washing the reaction product with anhydrous ethanol; finally, drying the product and grinding it into 60 mesh, thereby preparing the modified walnut biochar.

2. The potassium sulfate functional fertilizer for repairing heavy metals in soil according to claim 1, characterized in that: The components include, by weight, 50 parts of potassium sulfate, 10 parts of homemade graphene oxide bentonite composite material, 25 parts of modified walnut biochar, 5 parts of lignin sulfonate, and 2 parts of kaolin.

3. The potassium sulfate functional fertilizer for repairing heavy metals in soil according to claim 1, characterized in that: The lignin sulfonate is sodium lignin sulfonate.

4. The potassium sulfate functional fertilizer for repairing heavy metals in soil according to claim 1, characterized in that: The content of K2O in the potassium sulfate is 50-54%.

5. The potassium sulfate functional fertilizer for repairing heavy metals in soil according to claim 1, characterized in that: The concentration of NaOH solution is 0.5 mol / L.

6. The potassium sulfate functional fertilizer for repairing heavy metals in soil according to claim 1, characterized in that: The volume ratio of the mixed solvent of n-hexane and ethyl acetate is 1:

1.

7. The potassium sulfate functional fertilizer for repairing heavy metals in soil according to claim 1, characterized in that: The CAS number of the cysteamine hydrochloride is: 156-57-0.

8. The method for preparing a potassium sulfate functional fertilizer for repairing heavy metals in soil according to any one of claims 1 to 4, characterized in that: The preparation method of the potassium sulfate functional fertilizer for repairing heavy metals in soil is as follows: potassium sulfate, a homemade graphene oxide bentonite composite material, modified walnut biochar, and kaolin are weighed, and the mixture is placed in a mixing and stirring device, and the stirring device is started and stirred at 300 r / min for 20 minutes; Add lignin sulfonate to deionized water, stir and dissolve to prepare a 15% adhesive solution; Subsequently, the evenly mixed dry material is transferred to a disc granulator, the granulator is started, and the binder solution is slowly and evenly sprayed on the powder tumbling in the disc granulator, and the spraying amount and speed are controlled so that the particles gradually grow, so that the diameter of the formed potassium sulfate functional fertilizer is between 2-5 mm; finally, the prepared potassium sulfate functional fertilizer is evenly spread on a drying tray and placed in a blast drying oven, and the particles are dried at 70 degrees Celsius to constant weight; finally, potassium sulfate functional fertilizer with a diameter of 2-5 mm is prepared.

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