Potassium sulfate functional fertilizer for repairing soil heavy metals and preparation method of potassium sulfate functional fertilizer

Abstract

The invention discloses a potassium sulfate functional fertilizer for repairing soil heavy metals and a preparation method thereof, and belongs to the technical field of agricultural fertilizers. The fertilizer comprises the following components in parts by weight: 40-60 parts of potassium sulfate, 5-15 parts of a self-made graphene oxide bentonite composite material, 15-35 parts of modified walnut charcoal, 3-8 parts of lignosulfonate and 1-3 parts of kaolin. According to the preparation method, walnut biochar is adopted and is subjected to high-temperature pyrolysis activation, so that the prepared biochar has developed microporous and mesoporous structures, and a huge physical adsorption space can be provided; in addition, mercaptopropyl methyl dimethoxy silane modified charcoal is introduced, sulfydryl in the mercaptopropyl methyl dimethoxy silane modified charcoal serves as a soft base, the adsorption performance on soft acid of heavy metal elements such as cadmium, lead and mercury is high, potash fertilizer in the potassium sulfate fertilizer is basically not absorbed, target heavy metal ions can be selectively and powerfully captured, the potash fertilizer is not adsorbed, and the application prospect is wide. The potassium sulfate fertilizer can be efficiently utilized.

Description

Technical Field

[0001] The present invention belongs to the technical field of agricultural fertilizers. Specifically, it 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 pollutants. Soil is the ultimate destination of various heavy metal pollution sources such as the atmosphere, water, and agricultural production. Since soil is an extremely complex system with the coexistence of solid, liquid, and gas phases, soil environmental pollution is not as easily detected by people as air and water pollution. The concealment of soil heavy metal pollution, the long-term and irreversible nature of cumulative hazards determine that the repair of heavy metal contaminated soil is a very difficult and challenging task.

[0003] In fact, soil heavy metal pollution involves many aspects of industry, agriculture, human production and life. On the one hand, heavy metals can spread into the soil at all stages from ore mining until they become components in industrial products or finished products. On the other hand, agricultural production activities such as sewage irrigation, application of chemical fertilizers, municipal solid waste, sludge, and pesticides also increase the pollution load of heavy metals in the soil environment.

[0004] The existing technologies for repairing heavy metals in soil are as follows: a Chinese invention patent with the application number: CN201910383541.X discloses a multi-functional corn straw biochar composite fertilizer for repairing soil cadmium pollution and a preparation method thereof. It is characterized in that it is made of the following raw materials in parts by weight: 10 parts of composite fertilizer raw materials and 1 part of kaolin; the composite fertilizer raw materials are made of the following raw materials in parts by weight: 4 parts of composite biochar materials and 1 part of urea; the composite biochar materials are made of the following raw materials in parts by weight: 5-10 parts of corn straw, 1 part of triple superphosphate, and 1 part of diatomite; the preparation method of the multi-functional corn straw biochar composite fertilizer includes the following steps: Step 1: Dry and crush the corn straw; Step 2: Mix the corn straw, triple superphosphate, and diatomite evenly according to the ratio to obtain a mixed powder; Step 3: Place the mixed powder in a tube furnace for high-temperature pyrolysis, the pyrolysis temperature is 300-600°C, and the pyrolysis time is 1h to obtain composite biochar materials.

[0005] In the above-mentioned existing technology, the composite biochar materials used are prepared from corn straw, triple superphosphate, and diatomite. Although it has a better passivation effect on cadmium in the soil, the above-mentioned biochar materials will also enhance the adsorption of other cations such as potassium ions, which will greatly sacrifice the effectiveness of potassium fertilizers. And the ash content of corn straw biochar is high, the content of effective carbon skeletons in biochar per unit mass is small, and the high ash content may reduce the specific surface area and pore volume of biochar, greatly limiting its physical adsorption capacity.

[0006] 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 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 composite 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 the 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 heavy metals absorbed by crops during the long growth cycle are 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 prior art adopts a simple physical mixture of slow-release compound fertilizer particles and heavy metal adsorbents. However, in actual application, due to the influence of water migration in the soil and the complex ion diffusion path, the simple physical mixture of the above-mentioned prior art cannot ensure that the heavy metal adsorbent can capture the heavy metals in a timely and effective manner before they reach the root system of crops, nor can it prevent the potassium ions released by the slow-release compound fertilizer particles from contacting and adsorbing the adsorbent. This spatial and temporal uncertainty leads to the instability of the above-mentioned prior art in the control of heavy metals.

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

[0009] In order to solve the defects existing in the above technical solutions; the purpose of the present invention is to provide a potassium sulfate functional fertilizer for repairing soil heavy metals and a preparation method thereof. The purpose of the present invention can be achieved by the following technical solution: a potassium sulfate functional fertilizer for repairing soil heavy metals, which is composed of the following 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.

[0010] The preparation method of the self-made graphene oxide-bentonite composite material: ultrasonically disperse the modified graphene oxide in deionized water to obtain a modified graphene oxide suspension; ultrasonically disperse bentonite in deionized water to obtain a bentonite suspension; mix the two suspensions and transfer them to a three-necked flask, and introduce and maintain a nitrogen atmosphere; slowly add a NaOH solution to adjust the pH of the mixed suspension to 9; heat the reaction system to 65 °C, and add 10 ml of an aqueous solution of (NH4)2S2O8 dropwise. After 15 min, add 10 ml of an aqueous solution of NaHSO4 dropwise; continue stirring and reacting for 4 h; naturally cool to room temperature, and collect the product by suction filtration; wash the solid product with deionized water until the filtrate is neutral; wash it once with ethanol, and finally place it in a vacuum oven at 60 °C and dry it for 12 h until it reaches a constant weight, and grind it into powder, thus preparing the self-made 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 including the following steps: take 1 g of graphene oxide and place it in 500 mL of N,N-dimethylformamide, ultrasonically treat it for 30 minutes to obtain a uniformly dispersed graphene oxide dispersion; then introduce nitrogen for 30 minutes to create an inert environment; take another container, add 0.5 g of cysteamine hydrochloride and 0.5 g of 2,2'-azobisisobutyronitrile to 250 mL of N,N-dimethylformamide, ultrasonically treat it for 30 minutes to make a mixed solution; add the mixed solution to the dispersion; continue to introduce nitrogen for 30 minutes; seal the reaction mixture and place it in an oil bath at 70 °C, heat and stir for 12 hours; after the reaction is completed, cool to room temperature; centrifuge and filter to collect the product, and wash it 3-5 times with a mixed solvent of n-hexane and ethyl acetate, ethanol and distilled water in turn; finally, freeze-dry the washed product to prepare the modified graphene oxide.

[0013] Furthermore, the CAS number of the cysteamine hydrochloride is: 156-57-0; Furthermore, the volume ratio of the mixed solvent of n-hexane and ethyl acetate is 1:1; The biochar pretreatment: crush the walnut shell, grind it into powder, pass it through a 100-mesh sieve, and wash it with deionized water until the supernatant is clear; then place the washed walnut shell powder in an oven at 80 °C and dry it at a constant temperature for 12 hours, thus completing the pretreatment of the walnut shell powder; place the pretreated walnut shell powder in a crucible, put it into a muffle furnace, and introduce nitrogen to maintain an inert environment. Set the heating rate of the muffle furnace to 10 °C / min. After reaching 900 °C, continue pyrolyzing for 180 min to obtain walnut shell biochar. After the temperature naturally drops to room temperature, take it out, wash it with deionized water, and place it in an oven at 80 °C to dry, thus preparing the walnut biochar.

[0014] Preparation method of the modified walnut biochar: Add absolute ethanol and deionized water into a flask; stir magnetically and use 1 mol / L sodium hydroxide to adjust the pH of the solution to 11; weigh 6 g of mercaptopropylmethyldimethoxysilane and slowly add it into the mixed solution, and continue stirring for 30 min; then place the mixed solution under a nitrogen protection atmosphere, add walnut biochar into the reaction solution, and place the reaction vessel in an oil bath, heat up to 85 °C, and maintain reflux reaction for 12 h; after the reaction is completed, stop heating and naturally cool to room temperature under a nitrogen atmosphere; filter and collect the reaction product, wash the reaction product with absolute ethanol to remove the unreacted substances, and finally place the reaction product in a vacuum oven at 60 °C for drying and grind it to 60 mesh to prepare the modified walnut biochar.

[0015] Preparation method of a potassium sulfate functional fertilizer for repairing heavy metals in soil: Weigh potassium sulfate, self-made graphene oxide bentonite composite material, modified walnut biochar, and kaolin, and put them into a mixing and stirring device, start the stirring device and stir at 300 r / min for 20 min; add lignosulfonate into deionized water, stir and dissolve it to prepare an adhesive solution with a concentration of 15%; then transfer the uniformly mixed dry materials to a disk granulator, start the granulator, and slowly and uniformly spray the adhesive solution onto the powder tumbling in the disk granulator, control the liquid spraying amount and speed to make the particles gradually grow, so that the diameter of the formed potassium sulfate functional fertilizer is between 2 - 5 mm; finally, evenly spread the prepared potassium sulfate functional fertilizer on a baking tray and place it in a forced-air drying oven, dry the particles at 70 °C to constant weight; finally, prepare the potassium sulfate functional fertilizer with a diameter between 2 - 5 mm.

[0016] Furthermore, a potassium sulfate functional fertilizer for repairing heavy metals in soil, by weight, its components include: 50 parts of potassium sulfate, 10 parts of self-made graphene oxide bentonite composite material, 25 parts of modified walnut biochar, 5 parts of lignosulfonate, and 2 parts of kaolin.

[0017] Furthermore, the content of K2O in the potassium sulfate is 50 - 54%.

[0018] Furthermore, the lignosulfonate is sodium lignosulfonate.

[0019] The beneficial effects of the present invention are: 1. This application uses walnut biochar, which is activated by high-temperature pyrolysis. The prepared biochar has a developed microporous and mesoporous structure, which can provide a large physical adsorption space. In addition, this application introduces mercaptopropylmethyldimethoxysilane to modify the biochar. The mercapto group in it, as a soft base, has strong adsorption for soft acids such as heavy metal elements cadmium, lead, mercury, etc., and basically does not absorb potassium fertilizer in potassium sulfate fertilizer. It can selectively and strongly capture target heavy metal ions without adsorbing potassium fertilizer, enabling the efficient utilization of potassium sulfate fertilizer. 2. The self-made graphene oxide bentonite composite material of this application, in which the self-made graphene oxide is a nitrogen-containing chelating ligand with more adsorption sites. And with the use of an initiator, the self-made graphene oxide is effectively grafted on the surface of bentonite, firmly binding the self-made graphene oxide to the bentonite carrier and forming a stable three-dimensional network structure, making it less likely to dissociate in the soil environment. Moreover, the physical adsorption ability brought by the layered structure of the self-made graphene oxide enables these sites to be effectively exposed through grafting with bentonite, enabling more adsorption of heavy metals. 3. Through high-temperature treatment, this application can improve the graphitization degree of walnut biochar, thereby enhancing the π-electron system. And the self-made graphene oxide bentonite composite material in the components also contains a π-electron system. When the two are combined and used, the formed composite π-electron interface can provide stronger adsorption sites. Through the electron synergistic effect generated by the coupling of the π-electron systems, the potassium sulfate functional fertilizer exhibits better adsorption performance than single components. Detailed implementation mode

[0020] To make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments. The illustrative embodiments and descriptions of the present invention 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 intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated 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 range.

[0021] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention pertains. Although the present invention only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein can also be used in the implementation 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 related to the documents. In case of conflict with any incorporated document, the content of this specification shall prevail.

[0022] Without departing from the scope or spirit of the present invention, various improvements and changes can be made to the specific embodiments of the specification of the present invention, which will be obvious to those skilled in the art. Other embodiments obtained from the specification of the present invention will be obvious to those skilled in the art. The specification and examples of the present invention are merely exemplary.

[0023] Regarding the terms "comprising", "including", "having", "containing", etc. used herein, they are all open-ended terms, meaning including but not limited to.

[0024] The "parts" mentioned in the following examples are all parts by weight.

[0025] Example 1 A potassium sulfate functional fertilizer for repairing heavy metals in soil comprises: 40 parts of potassium sulfate, 5 parts of self-made graphene oxide bentonite composite material, 15 parts of modified walnut biochar, 3 parts of sodium lignosulfonate, and 1 part of kaolin; The kaolin is purchased from Guangzhou Zhanfei Chemical Technology Co., Ltd.; The graphene oxide is purchased from Shanghai Naiou Nano Technology Co., Ltd.; The modified graphene oxide is prepared by a method including the following steps: Take 1 g of graphene oxide and place it in 500 mL of N,N-dimethylformamide, and ultrasonically treat it for 30 minutes to obtain a uniformly dispersed graphene oxide dispersion; then introduce nitrogen for 30 minutes to create an inert environment; take another container, add 0.5 g of cysteamine hydrochloride and 0.5 g of 2,2'-azobisisobutyronitrile (initiator) into 250 mL of N,N-dimethylformamide, and ultrasonically treat it for 30 minutes to make a mixed solution; add this N,N-dimethylformamide mixed solution containing cysteamine hydrochloride and 2,2'-azobisisobutyronitrile to the above graphene oxide dispersion; then continue to introduce nitrogen for 30 minutes; transfer the reaction mixture to a round-bottom flask with magnetic stirring, seal it and place it in an oil bath at 70 °C for heating and stirring for 12 hours; after the reaction is completed, cool the product to room temperature; then collect the product by centrifugal filtration, and wash it thoroughly with a mixed solvent of n-hexane and ethyl acetate, ethanol and distilled water for 3-5 times; finally, freeze-dry the washed product to prepare the modified graphene oxide.

[0026] The CAS number of the cysteamine hydrochloride is: 156-57-0; The volume ratio of the mixed solvent of n-hexane and ethyl acetate is 1:1; Preparation method of self-made graphene oxide-bentonite composite material: Ultrasonically disperse 1 g of modified graphene oxide in 400 mL of deionized water for 1 hour to obtain a modified graphene oxide suspension; then ultrasonically disperse 3 g of bentonite in 200 mL of water for 30 min to obtain a uniform bentonite suspension; mix the modified graphene oxide suspension and the bentonite suspension, and transfer them to a three-necked flask with magnetic stirring. Introduce nitrogen for 30 min to remove dissolved oxygen and maintain a nitrogen atmosphere; slowly add 0.5 mol / L NaOH solution to adjust the pH of the mixed suspension to 9; heat the reaction system to 65 °C, and add 10 mL of 1% (NH4)2S2O8 aqueous solution dropwise. After 15 min, add 10 mL of 1% NaHSO4 aqueous solution dropwise; finally, keep the reaction temperature unchanged and continue to stir and react for 4 h; after natural cooling to room temperature, collect the solid product by suction filtration. Wash the solid product with deionized water until the filtrate is neutral; then wash it once with ethanol, and finally place it in a vacuum oven at 60 °C and dry it for 12 h until it reaches a constant weight, and grind it into powder to prepare the self-made graphene oxide-bentonite composite material.

[0027] The bentonite is sodium-based bentonite, purchased from Sichuan Hexin Runde Mining Co., Ltd.

[0028] Biochar pretreatment: Crush walnut shells, grind them into powder, pass through a 100-mesh sieve, and wash them with deionized water until the supernatant is clear; then place the washed walnut shell powder in an oven at 80 °C and dry it at a constant temperature for 12 hours to complete the pretreatment of the walnut shell powder; place the pretreated walnut shell powder in a crucible, put it into a muffle furnace, introduce nitrogen to maintain an inert environment, set the heating rate of the muffle furnace to 10 °C / min, after reaching 900 °C, continue pyrolysis for 180 min to obtain walnut shell biochar. After the temperature naturally drops to room temperature, take it out, wash it with deionized water and then place it in an oven at 80 °C to dry, and thus prepare walnut biochar.

[0029] Preparation method of modified walnut biochar: In a 500 ml flask, add 100 ml of absolute ethanol and 100 ml of deionized water; start magnetic stirring and use 1 mol / L sodium hydroxide to adjust the pH of the solution to 11; subsequently, weigh 6 g of mercaptopropylmethyldimethoxysilane and slowly add it to the mixed solution of water and ethanol with the adjusted pH, and continue stirring for 30 min; then place the mixed solution in an atmosphere protected by nitrogen, add the pretreated walnut biochar to the reaction solution under nitrogen atmosphere protection, place the reaction vessel in an oil bath, heat up to 85 °C, and maintain reflux reaction for 12 h; after the reaction is completed, stop heating and let the reaction system cool naturally to room temperature under nitrogen atmosphere; then filter to collect the reaction product, wash the reaction product with absolute ethanol to remove unreacted substances, and finally place the reaction product in a vacuum oven at 60 °C to dry to constant weight and grind it to 60 mesh, thus preparing the modified walnut biochar.

[0030] Preparation method of a potassium sulfate functional fertilizer for repairing heavy metals in soil: Weigh potassium sulfate, self-made graphene oxide bentonite composite material, modified walnut biochar, and kaolin, and put them into a mixing and stirring device, start the stirring device and stir at 300 r / min for 20 min; add lignosulfonate to deionized water, stir and dissolve it to prepare an adhesive solution with a concentration of 15%; then transfer the uniformly mixed dry materials to a disk granulator, start the granulator, and slowly and evenly spray the adhesive solution on the powder rolling in the disk granulator, control the liquid spraying amount and speed to make the particles gradually grow, so that the diameter of the formed potassium sulfate functional fertilizer is between 2 - 5 mm; finally, evenly spread the prepared potassium sulfate functional fertilizer on a baking tray and place it in a forced air drying oven, dry the particles at 70 °C to constant weight; finally, prepare the potassium sulfate functional fertilizer with a diameter between 2 - 5 mm.

[0031] Example 2 A potassium sulfate functional fertilizer for repairing heavy metals in soil includes: 45 parts of potassium sulfate, 8 parts of self-made graphene oxide bentonite composite material, 20 parts of modified walnut biochar, 4 parts of sodium lignosulfonate, and 2 parts of kaolin; Among them, the preparation methods of the self-made graphene oxide bentonite composite material, the modified walnut biochar, and the potassium sulfate functional fertilizer for repairing heavy metals in soil in Example 2 are all the same as those in Example 1.

[0032] Example 3 A potassium sulfate functional fertilizer for repairing heavy metals in soil includes: 50 parts of potassium sulfate, 10 parts of self-made graphene oxide bentonite composite material, 25 parts of modified walnut biochar, 5 parts of sodium lignosulfonate, and 2 parts of kaolin; Among them, the preparation methods of the self-made graphene oxide bentonite composite material, the modified walnut biochar, and the potassium sulfate functional fertilizer for repairing heavy metals in soil in Example 3 are all the same as those in Example 1.

[0033] Example 4 A potassium sulfate functional fertilizer for repairing heavy metals in soil includes: 55 parts of potassium sulfate, 12 parts of self-made graphene oxide bentonite composite material, 30 parts of modified walnut biochar, 7 parts of sodium lignosulfonate, and 3 parts of kaolin. Among them, the preparation methods of the self-made graphene oxide bentonite composite material, the modified walnut biochar, and the potassium sulfate functional fertilizer for repairing heavy metals in soil in Example 4 are all the same as those in Example 1.

[0034] Example 5 A potassium sulfate functional fertilizer for repairing heavy metals in soil includes: 60 parts of potassium sulfate, 15 parts of self-made graphene oxide bentonite composite material, 35 parts of modified walnut biochar, 8 parts of sodium lignosulfonate, and 3 parts of kaolin. Among them, the preparation methods of the self-made graphene oxide bentonite composite material, the modified walnut biochar, and the potassium sulfate functional fertilizer for repairing heavy metals in soil in Example 5 are all the same as those in Example 1.

[0035] Comparative Example 1 A potassium sulfate functional fertilizer for repairing heavy metals in soil includes: 50 parts of potassium sulfate, 5 parts of lignosulfonate, and 37 parts of kaolin; this Comparative Example 1 is based on Example 3, and the difference is that the addition of the self-made graphene oxide bentonite composite material and the modified walnut biochar is omitted, and their components are replaced with kaolin of the same weight; specifically, the 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.

[0036] Comparative Example 2 A potassium sulfate functional fertilizer for repairing heavy metals in soil includes: 50 parts of potassium sulfate, 10 parts of self-made graphene oxide bentonite composite material, 5 parts of lignosulfonate, and 27 parts of kaolin. This Comparative Example 2 is based on Example 3, and the difference is that the addition of the modified walnut biochar is omitted, and its components are replaced with kaolin of the same weight; Among them, the preparation methods of the self-made graphene oxide bentonite composite material and the potassium sulfate functional fertilizer for repairing heavy metals in soil in Comparative Example 2 are all the same as those in Example 3.

[0037] Comparative Example 3 A potassium sulfate functional fertilizer for repairing heavy metals in soil includes: 50 parts of potassium sulfate, 25 parts of modified walnut biochar, 5 parts of lignosulfonate, and 12 parts of kaolin. This Comparative Example 3 is based on Example 3, with the difference that the addition of the self-made graphene oxide bentonite composite material is omitted, and its components are replaced with kaolin of the same weight; Among them, 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 3 are both the same as those in Example 3.

[0038] Comparative Example 4 A potassium sulfate functional fertilizer for repairing heavy metals in soil includes: 50 parts of potassium sulfate, 10 parts of self-made graphene oxide bentonite composite material, 25 parts of walnut biochar, 5 parts of lignosulfonate, and 2 parts of kaolin; This Comparative Example 4 is based on Example 3, with the difference that the modification step of the walnut biochar is omitted, and its components are replaced with unmodified walnut biochar of the same weight; Among them, the preparation method of the self-made 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 the same as those in Example 3.

[0039] Comparative Example 5 A potassium sulfate functional fertilizer for repairing heavy metals in soil includes: 50 parts of potassium sulfate, 10 parts of graphene oxide bentonite composite material, 25 parts of modified walnut biochar, 5 parts of lignosulfonate, and 2 parts of kaolin; This Comparative Example 5 is based on Example 3, with the difference that the modification step of the graphene oxide bentonite composite material is omitted, and commercially available graphene oxide is directly used; 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 both the same as those in Example 3.

[0040] Test Example Soil from the surface layer of 0 - 20 cm of a polluted farmland around a certain mining area in Jiang'an County, Yibin City, Sichuan Province was collected. After the soil was naturally air-dried, it was passed through a 2 mm sieve. The basic physical and chemical properties of the soil are shown in Table 1.

[0041] Table 1

[0042] Weigh 10 kg of soil into a plastic bucket for each pot. The diameter of the bucket is 35 cm and the height is 40 cm. The following treatments are carried out: Add 20 g of the potassium sulfate functional fertilizer for repairing heavy metals in soil and sow corn. Cultivate the plants in a light incubator. After 45 days, when the corn grows to the seedling stage, harvest it, and take soil and plant samples for determination respectively.

[0043] Table 2

[0044] As shown in Table 2, in Examples 1-5 of the present application, the adsorption of heavy metals in soil can basically reach more than 80%, having excellent utility for repairing heavy metals in soil; the components of Comparative Example 1 include 50 parts of potassium sulfate, 5 parts of lignosulfonate, 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 enrich a part of heavy metals, so Comparative Example 1 also shows a certain heavy metal adsorption capacity.

[0045] In Comparative Example 2, the addition of modified walnut biochar was omitted, and in Comparative Example 3, the addition of self-made graphene oxide bentonite composite material was omitted; the adsorption effects of the two comparative examples are significantly stronger than that of Comparative Example 1, but there are obvious adsorption performance differences between them and Examples 1-5. The possible reasons are as follows: The modified walnut biochar in Examples 1-5, through high-temperature pyrolysis activation, makes the prepared biochar have a developed microporous and mesoporous structure, which can provide a huge physical adsorption space; and the present application introduces mercaptopropylmethyldimethoxysilane to modify the biochar. The mercapto group therein, as a soft base, has strong adsorption for soft acids such as heavy metal elements cadmium, lead, mercury, etc.; and a self-made graphene oxide bentonite composite material, in which the self-made graphene oxide is a nitrogen-containing chelating ligand, has more adsorption sites, and an initiator is used to effectively graft the self-made graphene oxide on the surface of bentonite, firmly bind the self-made graphene oxide to the bentonite carrier, and form a stable three-dimensional network structure, making it more difficult to dissociate in the soil environment; and the physical adsorption capacity brought by the layered structure of the self-made graphene oxide, through grafting and compounding with bentonite, enables these sites to be effectively exposed, and can complete more adsorption of heavy metals.

[0046] In Comparative Example 4, the modification step of 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 graphene oxide bentonite composite material was omitted; Comparative Examples 4 and 5 can also achieve better repair effects among Comparative Examples 1-5, but they cannot exceed 60%. The possible reason is that in Examples 1-5, through high-temperature treatment, the graphitization degree of walnut biochar can be improved, thereby enhancing the π-electron system, and the self-made graphene oxide bentonite composite material in the components also contains a π-electron system. When the two are used in combination, the formed composite π-electron interface can provide stronger adsorption sites, and through the electron synergy effect generated by the coupling of the π-electron systems, the potassium sulfate functional fertilizer shows more excellent adsorption and repair performance than single components.

[0047] Table 3

[0048] As shown in Table 3, in Comparative Example 1, the remediation of heavy metals in the soil was the weakest. In terms of plant height, because the high-concentration heavy metal stress in the soil had an obvious inhibitory effect on the division of plant cells, the cells could not divide normally in a short time, and chromosome mutations occurred, thus inhibiting the growth of plant seedlings. Therefore, Comparative Example 1 showed the lowest plant height.

[0049] In Examples 1-5, because the prepared biochar introduced mercaptopropylmethyldimethoxysilane-modified biochar, the mercapto group in it, as a soft base, had strong adsorption for soft acids such as heavy metal elements cadmium, lead, mercury, etc. It basically did not absorb the potassium fertilizer in potassium sulfate fertilizer. It could selectively and strongly capture target heavy metal ions without adsorbing potassium fertilizer, enabling the efficient utilization of potassium sulfate fertilizer. And potassium element could promote the cell division rate of meristematic tissue, resulting in relatively high plant heights in Examples 1-5. Although more potassium sulfate was added in Examples 4 and 5, the growth of the plants might still be affected by the heavy metal removal efficiency. However, the plant heights of the corn seedlings in Examples 1-5 were also significantly higher than those in the comparative examples.

[0050] The specific embodiments described above have further elaborated on the purpose, technical solutions, and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not used to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A potassium sulfate functional fertilizer for repairing heavy metals in soil, characterized in that, By weight parts, the composition is as follows, including: 40 - 60 parts of potassium sulfate, 5 - 15 parts of self-made graphene oxide bentonite composite material, 15 - 35 parts of modified walnut biochar, 3 - 8 parts of lignosulfonate, and 1 - 3 parts of kaolin.

2. The potassium sulfate functional fertilizer for repairing heavy metals in soil according to claim 1, characterized in that, By weight parts, its components include: 50 parts of potassium sulfate, 10 parts of self-made graphene oxide bentonite composite material, 25 parts of modified walnut biochar, 5 parts of lignosulfonate, 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 lignosulfonate is sodium lignosulfonate.

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 any one of claims 1-4, characterized in that, The preparation method of the self-made graphene oxide bentonite composite material is as follows: ultrasonically disperse the modified graphene oxide in deionized water to obtain a modified graphene oxide suspension; ultrasonically disperse bentonite in deionized water to obtain a bentonite suspension; mix the two suspensions and transfer them to a three-necked flask, and introduce and maintain a nitrogen atmosphere; slowly dropwise add NaOH solution to adjust the pH of the mixed suspension to 9; heat the reaction system to 65 °C, and sequentially dropwise add aqueous solutions of (NH4)2S2O8 and NaHSO4; continue stirring and reacting for 4 h; after naturally cooling to room temperature, filter to collect the product; wash the solid product and dry it to constant weight, and grind it into powder to prepare the self-made graphene oxide bentonite composite material.

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

7. The potassium sulfate functional fertilizer for repairing heavy metals in soil according to claim 5, characterized in that, The modified graphene oxide is prepared by a method including the following steps: place graphene oxide in N,N-dimethylformamide and ultrasonically treat it for 30 minutes to obtain a graphene oxide dispersion; then introduce nitrogen for 30 minutes; take another container, add cysteamine hydrochloride and 2,2'-azobisisobutyronitrile to N,N-dimethylformamide and ultrasonically treat it for 30 minutes to make a mixed solution; add the mixed solution to the dispersion; continue to introduce nitrogen for 30 minutes; seal the reaction mixture and place it in an oil bath at 70 °C, heat and stir for 12 hours; after the reaction is completed, cool to room temperature; centrifuge and filter to collect the product, and wash it 3 - 5 times with a mixed solvent of n-hexane and ethyl acetate, ethanol and distilled water; finally, freeze-dry the washed product to prepare the modified graphene oxide.

8. The potassium sulfate functional fertilizer for repairing heavy metals in soil according to claim 7, characterized in that, The volume ratio of the mixed solvent of n-hexane and ethyl acetate is 1:

1.

9. The potassium sulfate functional fertilizer for repairing heavy metals in soil according to any one of claims 1-4, characterized in that, The preparation method of the modified walnut biochar: add anhydrous ethanol and deionized water to a flask; stir magnetically and adjust the pH of the solution to 11 with sodium hydroxide; take 3-mercaptopropylmethyldimethoxysilane and add it to the mixed solution, and continue stirring for 30 min; then place the mixed solution under a nitrogen protection atmosphere, add walnut biochar to the reaction solution, and place the reaction vessel in an oil bath, heat to 85 °C, and maintain reflux reaction for 12 h; after the reaction is completed, stop heating, and naturally cool to room temperature under a nitrogen atmosphere; filter to collect the reaction product, and wash the reaction product with anhydrous ethanol; finally, dry and grind the product to 60 mesh to prepare the modified walnut biochar.

10. The preparation method of the potassium sulfate functional fertilizer for repairing heavy metals in soil according to any one of claims 1-4, characterized in that, The preparation method of the potassium sulfate functional fertilizer for repairing heavy metals in soil is as follows: Weigh potassium sulfate, self-made graphene oxide bentonite composite material, modified walnut biochar, and kaolin, and put them into a mixing and stirring device. Start the stirring device and stir at 300 r / min for 20 min; Add lignosulfonate to deionized water, stir and dissolve it to prepare an adhesive solution with a concentration of 15%; Subsequently, transfer the uniformly mixed dry materials to a disk granulator. Start the granulator, and slowly and evenly spray the adhesive solution onto the powder rolling in the disk granulator. Control the liquid spraying amount and speed to make the particles gradually grow, so that the diameter of the formed potassium sulfate functional fertilizer is between 2 - 5 mm. Finally, evenly spread the prepared potassium sulfate functional fertilizer on a baking tray and place it in a forced-air drying oven. Dry the particles at 70 °C until they reach a constant weight. Finally, the potassium sulfate functional fertilizer with a diameter of 2 - 5 mm is prepared.

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