A precipitation-loaded coated slow-release carbon-based iron fertilizer and its preparation method

Abstract

The invention discloses a precipitation-loaded coated slow-release carbon-based iron fertilizer and a preparation method thereof. The preparation method specifically comprises the following steps: impregnating a biological crustacean heavy metal adsorbent with a ferrous sulfate solution, drying the mixture at a low temperature, and then impregnating the mixture with a calcium hydroxide solution; and finally drying the obtained particles, granulating the particles, and performing a coating treatment. The coated slow-release iron fertilizer is loaded by precipitation, and a precipitated ferric hydroxide and ferrous hydroxide mixture thereof is uniformly dispersed and attached to the inside of pores of a porous adsorbent. The byproduct calcium sulfate in the porous adsorbent coats the precipitated ferric hydroxide and ferrous hydroxide, thereby achieving long-term slow-release of iron ions and reducing soil oxygen content. The coated iron fertilizer is used in a precise manner during the rice seedling raising period, and iron ion antagonism is performed throughout the entire rice growth process. The precipitation-type adsorption loading method greatly increases the release cycle of the iron ions. The iron fertilizer of the invention has an excellent cadmium and arsenic antagonistic effect on rice and has excellent application prospects.

Description

Technical Field

[0001] The present invention relates to the technical field of safe rice production in heavy metal-contaminated paddy fields, and in particular to a precipitation-loaded coated slow-release carbon-based iron fertilizer and a preparation method thereof. Background Art

[0002] In recent years, with the development of industry and the intensive use of agricultural inputs, the world has faced increasingly serious soil environmental safety issues, with heavy metal pollution receiving particular attention. In 1987, a study by the Lishui Health and Epidemic Prevention Station in Zhejiang Province revealed that cadmium levels in rice grown in the contaminated area near the Suichang gold mine were seriously exceeding standards. In 2002, the Ministry of Agriculture's Rice and Product Quality Supervision, Inspection, and Testing Center conducted safety inspections of rice sold nationwide, finding lead levels exceeding standards in 28.4% and cadmium levels in 10.3%. According to the 2014 National Soil Pollution Survey Report, jointly released by the Ministry of Environmental Protection and the Ministry of Land and Resources, the national soil pollution rate exceeded standards in 19.4%, with inorganic pollutants, primarily heavy metals (arsenic, as a metalloid element, is also classified as a heavy metal pollutant due to its similar health hazards to heavy metals), accounting for 82.8% of the total number of locations experiencing these levels. Due to current scientific limitations, heavy metal contaminants that enter the soil cannot be easily and quickly isolated. For the treatment of contaminated soil, the passivation / stabilization method is currently the main method used, that is, instead of reducing the total amount of heavy metals in the soil, technical means are used to reduce the mobility and bioavailability of pollutants, thereby curbing their impact and ecological risks, reducing the absorption of heavy metals by crops such as rice, and achieving safe production of agricultural products.

[0003] Extensive research has been conducted to develop inexpensive, readily available, and highly effective passivation materials. However, current passivation materials generally suffer from technical drawbacks such as high cost, insufficient long-term effectiveness, and high passivation dosage. Therefore, it is necessary to design a passivation material that can reduce the bioavailability of cadmium and arsenic in soil. Such a material should possess long-term effectiveness, i.e., a long-term antagonistic effect, and a significant passivation effect. Furthermore, the passivation dosage should be significantly reduced, thereby reducing remediation costs and improving the economic benefits of agricultural production. Summary of the Invention

[0004] The object of the present invention is to overcome the shortcomings of the prior art and provide a precipitation-loaded coated slow-release carbon-based iron fertilizer and a preparation method thereof. The preparation method is specifically as follows: a biological crustacean heavy metal adsorbent is impregnated with a ferrous sulfate solution, low-temperature drying is performed, and then the granules obtained by drying are granulated and coated. This coated slow-release iron fertilizer is loaded by precipitation, and the precipitated ferric hydroxide and ferrous hydroxide are uniformly dispersed and attached to the pores of the porous adsorbent. The byproduct calcium sulfate in the porous adsorbent wraps the precipitated ferric hydroxide and ferrous hydroxide, which can achieve long-term slow release of iron ions and can The invention reduces the oxygen content in the soil and cooperates with the precise use of coated iron fertilizer during the rice seedling raising period to carry out iron ion antagonism in the whole process of rice growth. The precipitation-type adsorption loading method and the coating material greatly increase the release cycle of iron ions. Compared with the traditional slow-release fertilizer, the iron fertilizer of the invention has an excellent cadmium and arsenic antagonistic effect on rice, and a small amount can greatly reduce the cadmium content of rice. In addition, since the invention is a coated slow-release fertilizer, the coating material remains stable during the rice seedling raising period. After transplanting into the field, the coating structure fails during the critical growth period when rice absorbs a large amount of heavy metals, and the slow-release ferric hydroxide and ferrous hydroxide begin to be released. At this time, if There is too much ferrous sulfate in the slow-release material that has not been completely precipitated. Ferrous sulfate will quickly enter the soil in large quantities in a short period of time and undergo hydrolysis in the water body, making the soil around the roots acidic, thereby activating the reduced heavy metals in the soil and transforming them from the passivated reduced state to the free ion state. A large number of heavy metal ions will accumulate around the roots in a short period of time. Other heavy metal ions in the soil will induce the rice roots to express transport proteins such as cadmium and arsenic ions, resulting in a decrease in the antagonistic effect of subsequent iron ion release, and losing the advantages of the coated slow-release material. Therefore, the coated slow-release fertilizer is concentrated on the seedling base during the seedling period. When the soil is in the soil, the ferrous sulfate content needs to be controlled. Therefore, the present invention impregnates ferrous sulfate in the front and calcium hydroxide in the back, so that the ferrous sulfate is basically consumed. The vast majority of the slow-release fertilizer is the by-product calcium sulfate encapsulating precipitated ferric hydroxide and ferrous hydroxide, thereby being able to provide iron ion antagonism for a long time. The ferric hydroxide and ferrous hydroxide precipitates are alkaline precipitates, which can control the soil pH and reduce the mobility of cadmium and arsenic. In addition, since the precipitation is generated in a porous material and has the covering and encapsulating effect of calcium sulfate particles, a portion of the ferrous hydroxide precipitate can be retained while generating the ferric hydroxide precipitate. After the ferrous hydroxide precipitate is released in the soil, it can quickly obtain oxygen in the soil, react with itself to generate ferric hydroxide precipitate, and also consume oxygen in the soil, thereby reducing the soil oxygen content, reducing the oxygen content in the rice rhizosphere, reducing the ionic conversion of heavy metals from reduced state to oxidized state, and not activating heavy metal ions in the soil. Multiple effects work together to achieve a better heavy metal antagonistic effect of the coated slow-release material.Furthermore, by precisely spreading a small amount of the coated slow-release material of the present invention onto the rice seedling tray during rice seedling cultivation, the coating structure of the slow-release material can be preserved intact for more than 30 days, thereby ensuring the integrity of the slow-release material during rice seedling cultivation and transplanting (or throwing). After rice transplanting (or throwing) in the field, the slow-release material is concentrated in high concentration in the rice rhizosphere and does not scatter between rice rows, reducing the loss of slow-release material scattered outside the rice root zone, thereby avoiding ineffective fertilizer application and reducing fertilizer usage. In summary, the present invention has excellent application prospects.

[0005] In order to achieve the above technical effects, the following technical solutions are adopted:

[0006] A method for preparing a precipitation-loaded coated slow-release carbon-based iron fertilizer comprises the following steps:

[0007] Step S1: crush the biocrust adsorbent into particles with a diameter of no more than 1 mm, impregnate with FeSO4 solution, filter and dry at low temperature;

[0008] Step S2: The biological crustacean adsorbent particles dried in step S1 are immersed in a Ca(OH)2 solution, removed from the solution, filtered, and then directly dried at low temperature and crushed into particles with a diameter of no more than 1 mm to obtain iron-based loaded biological crustacean particles;

[0009] Step S3: using an adhesive, granulating the iron-based loaded biological crustacean particles in step S2 according to a mass ratio, drying at a low temperature, and sieving after drying to obtain a precipitated loaded slow-release carbon-based iron fertilizer;

[0010] Step S4: preparing a water-based polyacrylate coating by an in-situ melting method, using the precipitated loaded slow-release carbon-based iron fertilizer in step S3 as the fertilizer core, and coating the fertilizer core at a fertilizer core coating mass ratio of 1: 1.0-1.3 to obtain a water-based polyacrylate coated iron fertilizer, that is, a precipitated loaded coated slow-release carbon-based iron fertilizer.

[0011] Furthermore, in step S1, the concentration of the Ca(OH)2 solution is 5% to 10%; the immersion time is more than 4 hours; and in step S2, the concentration of the FeSO4 solution is 5% to 10%; the immersion time is more than 4 hours.

[0012] Furthermore, the specific method for preparing the water-based polyacrylate coating by the in-situ melting method in step S4 is:

[0013] 8.24 g of nonionic emulsifier polyoxyethylene alkylphenyl ether OP-10, 4.12 g of anionic emulsifier sodium dodecylbenzene sulfonate SDBS and 31 g of hydrolysis inhibitor ethylene glycol EG were dissolved in 248 g of deionized water to prepare the aqueous phase; 110 g of butyl acrylate BA, 90 g of methyl methacrylate MMA and 3.5 g of functional monomer methacrylate MAA were mixed to prepare the organic phase; the two phases were stirred at 1000 rpm for 30 min at room temperature using a magnetic stirrer to prepare an oil-water mixture; the polymerization reaction was carried out at 80°C and 400 rpm. Initially, 25% of the oil-water mixture was added to a three-necked flask, and the remaining oil-water mixture and initiator solution were added alternately to the reaction system in four portions within 3 h. After the addition was completed, 5 g of methyl silicone oil was added to the round-bottom flask and the reaction was continued for 3 h; after the reaction was completed, the heater was turned off and the emulsion was passed through a 100-well stirring chamber when the temperature dropped to 40°C. The material was collected after filtration through a nylon mesh; the material was treated three times by a homogenizer at a pressure of 900 bar to obtain a water-based polyacrylate emulsion coating material; the initiator solution was 0.013 g mL -1 of K2S2O8, 52 mL.

[0014] Furthermore, the ratio of the concentration of the Ca(OH)2 solution to the concentration of the FeSO4 solution is 1.1-1.5:1, the volume ratio of the FeSO4 solution to the biological crustacean adsorbent particles in step S1 is 1-1.5:1; the volume ratio of the Ca(OH)2 solution in step S2 to the biological crustacean adsorbent particles dried in step S1 is 1.5-2:1;

[0015] Furthermore, the low-temperature drying temperature is 55-65°C.

[0016] Furthermore, the adhesive includes one or more of gypsum, quicklime, and slaked lime; water is added for bonding and then granulation is performed, and the amount of water added is 30-40% of the total mass of the adhesive; the mass ratio of the adhesive to the iron-based loaded biological crust particles is 1:3-1:5, and the precipitated loaded coated slow-release carbon-based iron fertilizer in step S3 is filtered through a mesh screen, and the particle size is 2-3 mm.

[0017] Furthermore, the mass ratio of the raw gypsum to the iron-based biological crust particles is 1:3, the mass ratio of the quicklime to the iron-based biological crust particles is 1:4, and the mass ratio of the slaked lime to the iron-based biological crust particles is 1:5.

[0018] Furthermore, the preparation method of the biological crustacean adsorbent is:

[0019] Treating the biocrust at 300-600° C. for 2-3 hours in the absence of oxygen, and modifying the treated biocrust to obtain the modified biocrust adsorbent;

[0020] Modification of the treated biocrusts includes the following steps:

[0021] Carboxymethylation: reacting the treated biocrust with chloroacetic acid in an alkaline solution to obtain a carboxymethylated biocrust; the alkaline solution is a 10% to 60% NaOH solution; the mass ratio of the treated biocrust: alkali: chloroacetic acid is 1: (2-4): (1.2-3);

[0022] Dialdehydeation: reacting carboxymethyl biocarapace with an oxidant to obtain dialdehyde carboxymethyl biocarapace; the oxidant is periodic acid and its salts; the mass ratio of the oxidant to the carboxymethyl biocarapace is (1-2):1;

[0023] Schiff base reaction: dialdehyde carboxymethyl biological crust is reacted with a water-soluble amino compound to obtain a dialdehyde carboxymethyl biological crust Schiff base; the water-soluble amino compound is one or more of aniline, benzylamine, phenylethylamine, m-aminophenol, n-hexylamine, n-octylamine, aminothiazole, m-phenylenediamine, p-phenylenediamine, o-phenylenediamine, aminobenzothiazole, and m-acetylaniline; the mass ratio of the water-soluble amino compound to the dialdehyde carboxymethyl biological crust is (1-5):1; the biological crust is one or more of shrimp shells, tortoise shells, crab shells, turtle shells, and fish scales.

[0024] A precipitation-loaded coated slow-release carbon-based iron fertilizer is prepared by any one of the above preparation methods.

[0025] A precise application method for a precipitated loaded coated slow-release carbon-based iron fertilizer comprises the following steps: a small amount of the precipitated loaded coated slow-release carbon-based iron fertilizer is applied to a rice seedling raising substrate during the rice seedling raising period; the rice root-wrapped seedling raising substrate or the root soil carried by the fertilizer is transferred to a production field during the rice seedling raising and transplanting process; and no secondary application in the field is required subsequently; the ratio of the rice seedling raising field area to the transplanting field area is 1:10-1:12; and the loaded coated slow-release carbon-based iron fertilizer is applied during the rice seedling raising process and introduced into the field during the transplanting process, which can substantially reduce the field usage of the coated slow-release carbon-based iron fertilizer and reduce the labor input for application.

[0026] The beneficial effects of the present invention are:

[0027] The present invention discloses a precipitation-loaded coated slow-release carbon-based iron fertilizer and a preparation method thereof. The preparation method is specifically as follows: a biological crustacean heavy metal adsorbent is impregnated with a ferrous sulfate solution, low-temperature dried and then impregnated again with a calcium hydroxide solution, and finally the dried particles are granulated and subjected to coating treatment. The coated slow-release iron fertilizer is loaded by precipitation, and its coating materials, precipitated ferric hydroxide and ferrous hydroxide, and calcium sulfate particles mixed with the precipitate generated simultaneously with the precipitation are uniformly dispersed and attached to the pores of the porous adsorbent for synergistic effect. The byproduct calcium sulfate in the porous adsorbent wraps the precipitated ferric hydroxide and ferrous hydroxide, which can achieve long-term slow-release of iron ions and reduce soil oxygen content. The coated iron fertilizer is used in a precise manner during the rice seedling raising period, and the coating material is used in a precise manner during the rice seedling raising period. During the seedling stage, the internal materials can be kept from contacting the outside world. After the seedling raising period, during the field growth process, the coating material loses its effectiveness. At this time, the biological crustacean adsorbent, the precipitated ferric hydroxide and ferrous hydroxide, and the calcium sulfate particles generated simultaneously with the precipitation and mixed with the precipitate work together to achieve long-term slow release of iron ions, perform iron ion antagonism throughout the entire rice growth process, and reduce the cadmium and arsenic ion absorption of rice. The precipitation-type loading method and the mixed coating of the reaction product calcium sulfate greatly improve the iron ion release pattern and speed through the adsorption and precipitation effect of the porous material, greatly increase the iron ion release cycle, and perform iron ion antagonism throughout the entire rice growth process. Compared with traditional slow-release fertilizers, the iron fertilizer of the present invention has excellent cadmium and arsenic antagonism of rice. A relatively small amount can significantly reduce the cadmium content in rice. In addition, since the present invention is a coated slow-release fertilizer, the coating material remains stable during the rice seedling raising period. After transplanting to the field, during the critical growth period when rice absorbs a large amount of heavy metals, the coating structure fails, and the slow-release ferric hydroxide and ferrous hydroxide begin to be released. At this time, if there is too much ferrous sulfate that has not completely reacted in the precipitation reaction in the slow-release material, the ferrous sulfate will quickly enter the soil in a short period of time and undergo a hydrolysis reaction in the water body, making the soil around the root system acidic, thereby activating the reduced heavy metals in the soil and causing them to transform from a passivated reduced state to a free ionic state. A large amount of heavy metal ions accumulate around the root system in a short period of time, and other heavy metal ions in the soil will induce the rice root system to express transport proteins such as cadmium and arsenic ions. This results in a reduced antagonistic effect after subsequent iron ion release, and the advantage of the coated slow-release material is lost. Therefore, when the coated slow-release fertilizer is used intensively in the seedling raising matrix during the seedling raising period, its ferrous sulfate content needs to be controlled. Therefore, the present invention impregnates ferrous sulfate in the front and calcium hydroxide in the back, so that the ferrous sulfate is basically completely consumed. The vast majority of the slow-release fertilizer is precipitated iron hydroxide and ferrous hydroxide wrapped with the by-product calcium sulfate, thereby being able to provide iron ion antagonism for a long time. The ferric hydroxide and ferrous hydroxide precipitates are alkaline precipitates, which can control the soil pH and reduce the mobility of cadmium and arsenic. In addition, since the precipitate is generated in a porous material and has the covering and wrapping effect of the calcium sulfate particles, a portion of the ferrous hydroxide precipitate can be retained while generating the iron hydroxide precipitate.After the ferrous hydroxide precipitate is released in the soil, it can quickly obtain oxygen in the soil, reacting itself to form ferric hydroxide precipitate. At the same time, it also consumes oxygen in the soil, reducing the soil oxygen content, reducing the oxygen content in the rice rhizosphere, reducing the ionic conversion of heavy metals from reduced state to oxidized state, and not activating heavy metal ions in the soil. Multiple effects work together to achieve a better heavy metal antagonism of the coated slow-release material. At the same time, by accurately sowing a small amount of the coated slow-release material of the present invention in the rice seedling tray during rice seedling cultivation, the coating structure of the slow-release material can be preserved intact for more than 30 days, thereby achieving the integrity of the slow-release material during rice seedling cultivation and transplanting (or throwing); after rice transplanting (or throwing) in the field, the slow-release material is concentrated in the rice rhizosphere at a high concentration and will not be scattered between the rice rows, reducing the loss of slow-release material scattered outside the rice root circle, thereby avoiding ineffective fertilizer application and reducing fertilizer usage. In summary, it has excellent application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a schematic diagram of a slow-release carbon-based iron fertilizer passivator in a rice seedling tray during rice seedling cultivation in a rice seedling field according to an embodiment of the present invention;

[0029] Figure 2 This is a schematic diagram of a slow-release carbon-based iron fertilizer passivator in a rice seedling tray during mechanized rice seedling tray cultivation according to an embodiment of the present invention. DETAILED DESCRIPTION

[0030] The present invention will be further described below with reference to the accompanying drawings, and the protection scope of the present invention is not limited to the following:

[0031] Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.

[0032] Example 1:

[0033] In this embodiment, the preparation method of the biological crustacean adsorbent is:

[0034] The biocrusts were treated at 300°C for 2 hours in the absence of oxygen.

[0035] Modifying the treated biological crust to obtain the modified biological crust adsorbent comprises the following steps:

[0036] Carboxymethylation: reacting the treated biocrust with chloroacetic acid in an alkaline solution to obtain a carboxymethylated biocrust; the alkaline solution is a 10% NaOH solution; the mass ratio of the treated biocrust: alkali: chloroacetic acid is 1:2:1.2;

[0037] Dialdehydeation: reacting carboxymethyl biocarapace with an oxidant to obtain dialdehyde carboxymethyl biocarapace; the oxidant is periodic acid; the mass ratio of the oxidant to the carboxymethyl biocarapace is 1:1;

[0038] Schiff base reaction: dialdehyde carboxymethyl biological crust is reacted with a water-soluble amino compound to obtain a dialdehyde carboxymethyl biological crust Schiff base; the water-soluble amino compound is aniline; the mass ratio of the water-soluble amino compound to the dialdehyde carboxymethyl biological crust is 1:1; the biological crust is shrimp shell.

[0039] The preparation method of a precipitation-loaded coated slow-release carbon-based iron fertilizer of this embodiment is as follows, comprising the following steps:

[0040] Step S1: crushing the biocrust adsorbent into particles with a diameter of no more than 1 mm, impregnating them with FeSO4 solution, filtering them to dryness, and then drying them at a low temperature of 55°C; the concentration of the FeSO4 solution is 5%; the impregnation time is more than 4 hours; the volume ratio of the FeSO4 solution to the biocrust adsorbent particles is 1:1;

[0041] Step S2: The biological crustacean adsorbent particles dried in step S1 are immersed in a Ca(OH)2 solution, removed, filtered, and then directly dried at low temperature and crushed into particles with a diameter of no more than 1 mm at a temperature of 55°C to obtain iron-based loaded biological crustacean particles; the concentration of the Ca(OH)2 solution is 5.5%; the immersion time is more than 4 hours; the volume ratio of the Ca(OH)2 solution to the biological crustacean adsorbent particles dried in step S1 is 1.5:1;

[0042] Step S3: using an adhesive, the adhesive includes gypsum, quicklime, and slaked lime; the mass ratio of gypsum to iron-based loaded biological crust particles is 1:3, the mass ratio of quicklime to iron-based loaded biological crust particles is 1:4, and the mass ratio of slaked lime to iron-based loaded biological crust particles is 1:5; adding water for bonding and then granulating, the amount of water added is 30% of the total mass of the adhesive; granulating the iron-based loaded biological crust particles in step S3 according to the mass ratio, low-temperature drying at a temperature of 50°C, and sieving after drying to obtain a precipitated loaded slow-release carbon-based iron fertilizer.

[0043] Step S4: preparing a water-based polyacrylate coating by an in-situ melting method, specifically:

[0044] 8.24 g of nonionic emulsifier polyoxyethylene alkylphenyl ether OP-10, 4.12 g of anionic emulsifier sodium dodecylbenzene sulfonate SDBS and 31 g of hydrolysis inhibitor ethylene glycol EG were dissolved in 248 g of deionized water to prepare the aqueous phase; 110 g of butyl acrylate BA, 90 g of methyl methacrylate MMA and 3.5 g of functional monomer methacrylate MAA were mixed to prepare the organic phase; the two phases were stirred at 1000 rpm for 30 min at room temperature using a magnetic stirrer to prepare an oil-water mixture; the polymerization reaction was carried out at 80°C and 400 rpm. Initially, 25% of the oil-water mixture was added to a three-necked flask, and the remaining oil-water mixture and initiator solution were added alternately to the reaction system in four portions within 3 h. After the addition was completed, 5 g of methyl silicone oil was added to the round-bottom flask and the reaction was continued for 3 h; after the reaction was completed, the heater was turned off and the emulsion was passed through a 100-well stirring chamber when the temperature dropped to 40°C. The material was collected after filtration through a nylon mesh; the material was treated three times by a homogenizer at a pressure of 900 bar to obtain a water-based polyacrylate emulsion coating material; the initiator solution was 0.013 g mL -1 of K2S2O8, 52 mL.

[0045] The precipitated loaded slow-release carbon-based iron fertilizer in step S3 is used as the fertilizer core, and the water-based polyacrylate coated iron fertilizer is prepared by coating at a fertilizer core coating mass ratio of 1: 1, thereby obtaining a precipitated loaded coated slow-release carbon-based iron fertilizer 1.

[0046] Example 2:

[0047] In this embodiment, the preparation method of the biological crustacean adsorbent is:

[0048] The bio-crusts were treated at 600°C for 3 hours in the absence of oxygen.

[0049] Modifying the treated biological crust to obtain the modified biological crust adsorbent comprises the following steps:

[0050] Carboxymethylation: reacting the treated biocrust with chloroacetic acid in an alkaline solution to obtain a carboxymethylated biocrust; the alkaline solution is a 60% NaOH solution; the mass ratio of the treated biocrust: alkali: chloroacetic acid is 1:4:3;

[0051] Dialdehydeation: reacting carboxymethyl biocarapace with an oxidant to obtain dialdehyde carboxymethyl biocarapace; the oxidant is periodic acid; the mass ratio of the oxidant to the carboxymethyl biocarapace is 2:1;

[0052] Schiff base reaction: dialdehyde carboxymethyl biological crust is reacted with a water-soluble amino compound to obtain a dialdehyde carboxymethyl biological crust Schiff base; the water-soluble amino compound is benzylamine; the mass ratio of the water-soluble amino compound to the dialdehyde carboxymethyl biological crust is 5:1; the biological crust is crab shell.

[0053] The preparation method of a precipitation-loaded coated slow-release carbon-based iron fertilizer of this embodiment is as follows, comprising the following steps:

[0054] Step S1: crushing the biocrust adsorbent into particles with a diameter of no more than 1 mm, impregnating them with FeSO4 solution, filtering them to dryness, and then drying them at a low temperature of 65°C; the concentration of the FeSO4 solution is 6.67%; the impregnation time is more than 4 hours; and the volume ratio of the FeSO4 solution to the biocrust adsorbent particles is 1.5:1;

[0055] Step S2: The biological crustacean adsorbent particles dried in step S1 are immersed in a Ca(OH)2 solution, removed, filtered, and then directly dried at low temperature and crushed into particles with a diameter of no more than 1 mm at a temperature of 65°C to obtain iron-based loaded biological crustacean particles; the concentration of the Ca(OH)2 solution is 10%; the immersion time is more than 4 hours; the volume ratio of the Ca(OH)2 solution to the biological crustacean adsorbent particles dried in step S1 is 2:1;

[0056] Step S3: using an adhesive, the adhesive includes gypsum, quicklime, and slaked lime; the mass ratio of gypsum to iron-based loaded biological crust particles is 1:3, the mass ratio of quicklime to iron-based loaded biological crust particles is 1:4, and the mass ratio of slaked lime to iron-based loaded biological crust particles is 1:5; adding water for bonding and then granulating, the amount of water added is 30% of the total mass of the adhesive; granulating the iron-based loaded biological crust particles in step S3 according to the mass ratio, low-temperature drying at a temperature of 55°C, and sieving after drying to obtain a precipitated loaded slow-release carbon-based iron fertilizer.

[0057] Step S4: preparing a water-based polyacrylate coating by an in-situ melting method, specifically:

[0058] 8.24 g of nonionic emulsifier polyoxyethylene alkylphenyl ether OP-10, 4.12 g of anionic emulsifier sodium dodecylbenzene sulfonate SDBS and 31 g of hydrolysis inhibitor ethylene glycol EG were dissolved in 248 g of deionized water to prepare the aqueous phase; 110 g of butyl acrylate BA, 90 g of methyl methacrylate MMA and 3.5 g of functional monomer methacrylate MAA were mixed to prepare the organic phase; the two phases were stirred at 1000 rpm for 30 min at room temperature using a magnetic stirrer to prepare an oil-water mixture; the polymerization reaction was carried out at 80°C and 400 rpm. Initially, 25% of the oil-water mixture was added to a three-necked flask, and the remaining oil-water mixture and initiator solution were added alternately to the reaction system in four portions within 3 h. After the addition was completed, 5 g of methyl silicone oil was added to the round-bottom flask and the reaction was continued for 3 h; after the reaction was completed, the heater was turned off and the emulsion was passed through a 100-well stirring chamber when the temperature dropped to 40°C. The material was collected after filtration through a nylon mesh; the material was treated three times by a homogenizer at a pressure of 900 bar to obtain a water-based polyacrylate emulsion coating material; the initiator solution was 0.013 g mL -1 of K2S2O8, 52 mL.

[0059] The precipitated loaded slow-release carbon-based iron fertilizer in step S3 is used as the fertilizer core, and the fertilizer core coating mass ratio is 1: 1.3 to prepare a water-based polyacrylate coated iron fertilizer, thereby obtaining a precipitated loaded coated slow-release carbon-based iron fertilizer 2.

[0060] Comparative Example 1:

[0061] Based on Example 1:

[0062] In this comparative example, the preparation method of the biological crustacean adsorbent is the same as that in Example 1.

[0063] The preparation method of a common loaded slow-release carbon-based iron fertilizer in this comparative example is as follows, comprising the following steps:

[0064] Step S1: crushing the biological crustacean adsorbent into particles with a diameter not greater than 1 mm, immersing the particles in a FeSO4 solution, removing the particles from the solution, filtering them, and then directly drying them at low temperature at 55°C to crush them into particles with a diameter not greater than 1 mm, thereby obtaining iron-based loaded biological crustacean particles; the FeSO4 solution concentration is 5%; the immersion time is more than 4 hours; and the volume ratio of the FeSO4 solution to the biological crustacean adsorbent particles is 1:1;

[0065] Step S2: using an adhesive, the adhesive includes gypsum, quicklime, and slaked lime; the mass ratio of quicklime to iron-based loaded biological crust particles is 1:3, the mass ratio of quicklime to iron-based loaded biological crust particles is 1:4, and the mass ratio of slaked lime to iron-based loaded biological crust particles is 1:5; adding water for bonding and then granulating, the amount of water added is 30% of the total mass of the adhesive; granulating the iron-based loaded biological crust particles in step S2 according to the mass ratio, drying at a low temperature of 50°C, and sieving after drying to obtain a common loaded slow-release carbon-based iron fertilizer.

[0066] Step S3: preparing a water-based polyacrylate coating by an in-situ melting method, specifically:

[0067] 8.24 g of nonionic emulsifier polyoxyethylene alkylphenyl ether OP-10, 4.12 g of anionic emulsifier sodium dodecylbenzene sulfonate SDBS and 31 g of hydrolysis inhibitor ethylene glycol EG were dissolved in 248 g of deionized water to prepare the aqueous phase; 110 g of butyl acrylate BA, 90 g of methyl methacrylate MMA and 3.5 g of functional monomer methacrylate MAA were mixed to prepare the organic phase; the two phases were stirred at 1000 rpm for 30 min at room temperature using a magnetic stirrer to prepare an oil-water mixture; the polymerization reaction was carried out at 80°C and 400 rpm. Initially, 25% of the oil-water mixture was added to a three-necked flask, and the remaining oil-water mixture and initiator solution were added alternately to the reaction system in four portions within 3 h. After the addition was completed, 5 g of methyl silicone oil was added to the round-bottom flask and the reaction was continued for 3 h; after the reaction was completed, the heater was turned off and the emulsion was passed through a 100-well stirring chamber when the temperature dropped to 40°C. The material was collected after filtration through a nylon mesh; the material was treated three times by a homogenizer at a pressure of 900 bar to obtain a water-based polyacrylate emulsion coating material; the initiator solution was 0.013 g mL -1 of K2S2O8, 52 mL.

[0068] The ordinary loaded slow-release carbon-based iron fertilizer in step S2 is used as the fertilizer core, and the water-based polyacrylate coated iron fertilizer is prepared by coating at a fertilizer core coating mass ratio of 1: 1, thereby obtaining the ordinary loaded coated slow-release carbon-based iron fertilizer 3.

[0069] Comparative Example 2:

[0070] Based on Example 1:

[0071] In this comparative example, the preparation method of the biological crustacean adsorbent is the same as that in Example 1.

[0072] The preparation method of a common loaded slow-release carbon-based iron fertilizer in this comparative example is as follows, comprising the following steps:

[0073] Step S1: crushing the biocrust adsorbent into particles with a diameter not greater than 1 mm, immersing the particles in a Ca(OH)2 solution, removing the particles from the solution, filtering them, and then directly drying them at low temperature at 55°C to crush them into particles with a diameter not greater than 1 mm, thereby obtaining loaded biocrust particles; the concentration of the Ca(OH)2 solution is 5.5%; the immersion time is more than 4 hours; and the volume ratio of the Ca(OH)2 solution to the biocrust adsorbent particles is 1.5:1;

[0074] Step S2: using an adhesive, the adhesive including gypsum, quicklime, and slaked lime; the mass ratio of gypsum to the loaded biological crustacean particles is 1:3, the mass ratio of quicklime to the loaded biological crustacean particles is 1:4, and the mass ratio of slaked lime to the loaded biological crustacean particles is 1:5; adding water for bonding and then granulating, the amount of water added is 30% of the total mass of the adhesive; granulating the loaded biological crustacean particles in step S2 according to the mass ratio, drying at a low temperature of 50°C, and sieving after drying to obtain a common loaded slow-release carbon-based iron fertilizer.

[0075] Step S3: preparing a water-based polyacrylate coating by an in-situ melting method, specifically:

[0076] 8.24 g of nonionic emulsifier polyoxyethylene alkylphenyl ether OP-10, 4.12 g of anionic emulsifier sodium dodecylbenzene sulfonate SDBS and 31 g of hydrolysis inhibitor ethylene glycol EG were dissolved in 248 g of deionized water to prepare the aqueous phase; 110 g of butyl acrylate BA, 90 g of methyl methacrylate MMA and 3.5 g of functional monomer methacrylate MAA were mixed to prepare the organic phase; the two phases were stirred at 1000 rpm for 30 min at room temperature using a magnetic stirrer to prepare an oil-water mixture; the polymerization reaction was carried out at 80°C and 400 rpm. Initially, 25% of the oil-water mixture was added to a three-necked flask, and the remaining oil-water mixture and initiator solution were added alternately to the reaction system in four portions within 3 h. After the addition was completed, 5 g of methyl silicone oil was added to the round-bottom flask and the reaction was continued for 3 h; after the reaction was completed, the heater was turned off and the emulsion was passed through a 100-well stirring chamber when the temperature dropped to 40°C. The material was collected after filtration through a nylon mesh; the material was treated three times by a homogenizer at a pressure of 900 bar to obtain a water-based polyacrylate emulsion coating material; the initiator solution was 0.013 g mL -1 of K2S2O8, 52 mL.

[0077] The ordinary loaded slow-release carbon-based iron fertilizer in step S2 is used as the fertilizer core, and the fertilizer core coating mass ratio is 1: 1 to prepare a water-based polyacrylate coated fertilizer, that is, the ordinary loaded coated slow-release carbon-based fertilizer 4.

[0078] Comparative Example 3:

[0079] In this comparative example, the preparation method of the biological crustacean adsorbent is the same as that in Example 1.

[0080] The preparation method of a common loaded slow-release carbon-based iron fertilizer in this comparative example is as follows, comprising the following steps:

[0081] Step S1: Loading with ferric hydroxide powder: The biocrust adsorbent is crushed into particles with a diameter of no more than 1 mm. 3 parts by weight of the biocrust adsorbent particles and 8 parts by weight of ferric hydroxide powder are mixed evenly, and the mixture is placed in a shaking device for shaking. After the shaking is completed, the biocrust adsorbent particles loaded with ferric hydroxide powder are separated using a screening device for later use;

[0082] Step S2: using an adhesive, the adhesive includes gypsum, quicklime, and slaked lime; the mass ratio of quicklime to the biological crustacean adsorbent particles loaded with iron hydroxide powder is 1:3, the mass ratio of quicklime to the biological crustacean adsorbent particles loaded with iron hydroxide powder is 1:4, and the mass ratio of slaked lime to the biological crustacean adsorbent particles loaded with iron hydroxide powder is 1:5; adding water for bonding and then granulating, the amount of water added is 30% of the total mass of the adhesive; granulating the biological crustacean adsorbent particles loaded with iron hydroxide powder in step S1 according to the mass ratio, drying at a low temperature of 50°C, and sieving after drying to obtain a common loaded slow-release carbon-based iron fertilizer.

[0083] Step S3: preparing a water-based polyacrylate coating by an in-situ melting method, specifically:

[0084] 8.24 g of nonionic emulsifier polyoxyethylene alkylphenyl ether OP-10, 4.12 g of anionic emulsifier sodium dodecylbenzene sulfonate SDBS and 31 g of hydrolysis inhibitor ethylene glycol EG were dissolved in 248 g of deionized water to prepare the aqueous phase; 110 g of butyl acrylate BA, 90 g of methyl methacrylate MMA and 3.5 g of functional monomer methacrylate MAA were mixed to prepare the organic phase; the two phases were stirred at 1000 rpm for 30 min at room temperature using a magnetic stirrer to prepare an oil-water mixture; the polymerization reaction was carried out at 80°C and 400 rpm. Initially, 25% of the oil-water mixture was added to a three-necked flask, and the remaining oil-water mixture and initiator solution were added alternately to the reaction system in four portions within 3 h. After the addition was completed, 5 g of methyl silicone oil was added to the round-bottom flask and the reaction was continued for 3 h; after the reaction was completed, the heater was turned off and the emulsion was passed through a 100-well stirring chamber when the temperature dropped to 40°C. The material was collected after filtration through a nylon mesh; the material was treated three times by a homogenizer at a pressure of 900 bar to obtain a water-based polyacrylate emulsion coating material; the initiator solution was 0.013 g mL -1 of K2S2O8, 52 mL.

[0085] The ordinary loaded slow-release carbon-based iron fertilizer in step S2 is used as the fertilizer core, and the water-based polyacrylate coated iron fertilizer is prepared by coating at a fertilizer core coating mass ratio of 1: 1, thereby obtaining ordinary loaded coated slow-release carbon-based iron fertilizer 5.

[0086] Comparative Example 4:

[0087] In this comparative example, the preparation method of the biological crustacean adsorbent is the same as that in Example 1.

[0088] The preparation method of a precipitated loaded slow-release carbon-based iron fertilizer of this comparative example is as follows, comprising the following steps:

[0089] Step S1: crushing the biocrust adsorbent into particles with a diameter of no more than 1 mm, impregnating them with a Ca(OH)2 solution, filtering them to dryness, and then drying them at a low temperature of 55°C; the concentration of the Ca(OH)2 solution is 5%; the impregnation time is more than 4 hours; the volume ratio of the Ca(OH)2 solution to the biocrust adsorbent particles is 1:1;

[0090] Step S2: The biological crustacean adsorbent particles dried in step S1 are immersed in a FeSO4 solution, removed, filtered, and then directly dried at low temperature and crushed into particles with a diameter of no more than 1 mm at a temperature of 55°C to obtain iron-based loaded biological crustacean particles; the concentration of the FeSO4 solution is 5.5%; the immersion time is more than 4 hours; the volume ratio of the FeSO4 solution to the biological crustacean adsorbent particles dried in step S1 is 1.5:1;

[0091] Step S3: using an adhesive, the adhesive comprising gypsum, quicklime, and slaked lime; the mass ratio of quicklime to iron-based biocrust particles with a slight excess of ferrous sulfate is 1:3, the mass ratio of quicklime to iron-based biocrust particles with a slight excess of ferrous sulfate is 1:4, and the mass ratio of slaked lime to iron-based biocrust particles with a slight excess of ferrous sulfate is 1:5; adding water for bonding and then granulating, wherein the amount of water added is 30% of the total mass of the adhesive; granulating the iron-based biocrust particles with a slight excess of ferrous sulfate in step S2 according to the mass ratio, drying at a low temperature of 50° C., and sieving after drying to obtain a particle size of 2 mm; thereby obtaining a precipitated slow-release carbon-based iron fertilizer;

[0092] Step S5: preparing a water-based polyacrylate coating by an in-situ melting method, specifically:

[0093] 8.24 g of nonionic emulsifier polyoxyethylene alkylphenyl ether OP-10, 4.12 g of anionic emulsifier sodium dodecylbenzene sulfonate SDBS and 31 g of hydrolysis inhibitor ethylene glycol EG were dissolved in 248 g of deionized water to prepare the aqueous phase; 110 g of butyl acrylate BA, 90 g of methyl methacrylate MMA and 3.5 g of functional monomer methacrylate MAA were mixed to prepare the organic phase; the two phases were stirred at 1000 rpm for 30 min at room temperature using a magnetic stirrer to prepare an oil-water mixture; the polymerization reaction was carried out at 80°C and 400 rpm. Initially, 25% of the oil-water mixture was added to a three-necked flask, and the remaining oil-water mixture and initiator solution were added alternately to the reaction system in four portions within 3 h. After the addition was completed, 5 g of methyl silicone oil was added to the round-bottom flask and the reaction was continued for 3 h; after the reaction was completed, the heater was turned off and the emulsion was passed through a 100-well stirring chamber when the temperature dropped to 40°C. The material was collected after filtration through a nylon mesh; the material was treated three times by a homogenizer at a pressure of 900 bar to obtain a water-based polyacrylate emulsion coating material; the initiator solution was 0.013 g mL -1 of K2S2O8, 52 mL.

[0094] The precipitated loaded slow-release carbon-based iron fertilizer in step S3 is used as the fertilizer core, and the fertilizer core coating mass ratio is 1: 1 to prepare a water-based polyacrylate coated iron fertilizer, that is, a precipitated loaded coated slow-release carbon-based iron fertilizer 6.

[0095] Comparative Example 5:

[0096] In this comparative example, the preparation method of the biological crustacean adsorbent is the same as that in Example 1.

[0097] The preparation method of a precipitated loaded slow-release carbon-based iron fertilizer of this comparative example is as follows, comprising the following steps:

[0098] Step S1: crushing the biocrust adsorbent into particles with a diameter of no more than 1 mm, impregnating them with a Ca(OH)2 solution, filtering them to dryness, and then drying them at a low temperature of 55°C; the concentration of the Ca(OH)2 solution is 5%; the impregnation time is more than 4 hours; the volume ratio of the Ca(OH)2 solution to the biocrust adsorbent particles is 1:1;

[0099] Step S2: The biological crustacean adsorbent particles dried in step S1 are immersed in a FeSO4 solution, removed, filtered, and then directly dried at low temperature and crushed into particles with a diameter of no more than 1 mm at a temperature of 55°C to obtain iron-based loaded biological crustacean particles; the concentration of the FeSO4 solution is 5.5%; the immersion time is more than 4 hours; the volume ratio of the FeSO4 solution to the biological crustacean adsorbent particles dried in step S1 is 1.5:1;

[0100] Step S3: The iron-based loaded biological crust particles dried in step S2 are immersed in the FeSO4 solution again, removed and filtered, and then directly dried at low temperature and crushed into particles with a diameter of no more than 1 mm at a temperature of 55°C to obtain iron-based loaded biological crust particles with excess ferrous sulfate; the concentration of the FeSO4 solution is 5.5%; the immersion time is more than 1 hour; the volume ratio of the FeSO4 solution to the biological crust adsorbent particles dried in step S2 is 1:1.

[0101] Step S4: using an adhesive, the adhesive comprising gypsum, quicklime, and slaked lime; the mass ratio of quicklime to iron-based biocrust particles with excess ferrous sulfate is 1:3, the mass ratio of quicklime to iron-based biocrust particles with excess ferrous sulfate is 1:4, and the mass ratio of slaked lime to iron-based biocrust particles with excess ferrous sulfate is 1:5; adding water for bonding and then granulating, wherein the amount of water added is 30% of the total mass of the adhesive; granulating the iron-based biocrust particles with excess ferrous sulfate in step S3 according to the mass ratio, drying at a low temperature of 50° C., and sieving after drying to obtain a particle size of 2 mm; thereby obtaining a precipitated slow-release carbon-based iron fertilizer;

[0102] Step S5: preparing a water-based polyacrylate coating by an in-situ melting method, specifically:

[0103] 8.24 g of nonionic emulsifier polyoxyethylene alkylphenyl ether OP-10, 4.12 g of anionic emulsifier sodium dodecylbenzene sulfonate SDBS and 31 g of hydrolysis inhibitor ethylene glycol EG were dissolved in 248 g of deionized water to prepare the aqueous phase; 110 g of butyl acrylate BA, 90 g of methyl methacrylate MMA and 3.5 g of functional monomer methacrylate MAA were mixed to prepare the organic phase; the two phases were stirred at 1000 rpm for 30 min at room temperature using a magnetic stirrer to prepare an oil-water mixture; the polymerization reaction was carried out at 80°C and 400 rpm. Initially, 25% of the oil-water mixture was added to a three-necked flask, and the remaining oil-water mixture and initiator solution were added alternately to the reaction system in four portions within 3 h. After the addition was completed, 5 g of methyl silicone oil was added to the round-bottom flask and the reaction was continued for 3 h; after the reaction was completed, the heater was turned off and the emulsion was passed through a 100-well stirring chamber when the temperature dropped to 40°C. The material was collected after filtration through a nylon mesh; the material was treated three times by a homogenizer at a pressure of 900 bar to obtain a water-based polyacrylate emulsion coating material; the initiator solution was 0.013 g mL -1 of K2S2O8, 52 mL.

[0104] The precipitated loaded slow-release carbon-based iron fertilizer in step S4 is used as the fertilizer core, and the fertilizer core coating mass ratio is 1: 1 to prepare a water-based polyacrylate coated iron fertilizer, that is, a precipitated loaded coated slow-release carbon-based iron fertilizer 7.

[0105] Comparative Example 6:

[0106] In this comparative example, the preparation method of the biological crustacean adsorbent is the same as that in Example 1. The only difference is that in step S4, the water-based polyacrylate-coated iron fertilizer is coated at a fertilizer core coating mass ratio of 1:0.5 to obtain the precipitation-loaded coated slow-release carbon-based iron fertilizer 8.

[0107] Comparative Example 7:

[0108] In this comparative example, the preparation method of the biological crustacean adsorbent is the same as that in Example 1. The only difference is that in step S4, the water-based polyacrylate-coated iron fertilizer is coated at a fertilizer core coating mass ratio of 1:2 to obtain the precipitation-loaded coated slow-release carbon-based iron fertilizer 9.

[0109] The slow-release carbon-based iron fertilizers in Examples 1-2 and Comparative Examples 1-7 are evaluated below:

[0110] The experiment was conducted in a paddy field with a pH of 5.33, a total cadmium content of 0.71 mg / kg, a total arsenic content of 53 mg / kg, and an organic matter content of 28.1 g / kg. The soil was a latent paddy soil with medium overall fertility. The entire field was divided into 30 plots, each with an area of ​​30 m 2 , every 3 plots were a treatment area, with a total of 10 treatment areas, treatment area 1 was the blank control group CK (no slow-release carbon-based iron fertilizer passivation agent was applied), and treatment areas 2-10 were the slow-release carbon-based iron fertilizer passivation agents in Examples 1-2 and Comparative Examples 1-7, respectively; the same rice variety was planted in all of them, namely Taiyou 398.

[0111] Rice seedlings are raised in the field or in mechanized rice seedling trays. During the preparation of rice seedling trays, a total of 9 slow-release carbon-based iron fertilizer passivators according to Examples 1-2 and Comparative Examples 1-7 (3 plots for each slow-release carbon-based iron fertilizer passivator) are evenly applied to the rice seedling trays at a rate of 30 kg / mu for the rice seedling field (the ratio of the rice seedling field to the transplanted field area is 1:10, and the actual field rate is 3 kg / mu), and the rice seedling trays are covered with rice seedling soil. The application effect is as follows: Figure 1 and Figure 2 A control treatment (CK) was also established. No slow-release carbon-based iron fertilizer passivator was used during the seedling raising process (3 plots). Germinated rice seeds were evenly sown in seedling trays and transplanted after approximately 20 days of seedling raising.

[0112] Two days before transplanting rice, apply 45 kg / mu of compound fertilizer (total nutrient content 45%, with N-P₂O₅-K₂O = 15-15-15). Transplant rice seedlings by broadcasting (under field-raised seedling conditions) or mechanical transplanting (under mechanized seedling cultivation), carrying the root soil or seedling substrate with them. Apply 8 kg / mu of urea during the tillering stage. Other field water and fertilizer management practices and pest and disease control measures remain the same as traditional methods. After rice matures, harvest and measure yield in each plot, and determine cadmium and arsenic content in the rice.

[0113] The cadmium and arsenic content in brown rice was determined by adding 5 mL of nitric acid and 3.0 mL of hydrogen peroxide solution to a 0.1 g sample of brown rice powder. The mixture was covered and cold digested overnight. The digestion was continued for 2 h in a graphite digester and the volume was adjusted to 25 mL. The cadmium and arsenic concentrations in the digestion solution were analyzed using inductively coupled plasma mass spectrometry. The test results are shown in Table 1.

[0114] Table 1 Differences in rice yield and cadmium and arsenic content in brown rice among treatments

[0115] Processing Area deal with Rice yield (kg / mu) Cadmium content in brown rice (mg / kg) Arsenic content in rice (mg / kg) 1 Blank control CK 535±28 0.660±0.079 0.596±0.053 2 Example 1 562±16 0.097±0.012 0.143±0.022 3 Example 2 558±20 0.093±0.013 0.147±0.023 4 Comparative Example 1 541±27 0.432±0.021 0.502±0.062 5 Comparative Example 2 530±23 0.531±0.031 0.534±0.052 6 Comparative Example 3 542±17 0.354±0.052 0.417±0.038 7 Comparative Example 4 541±10 0.149±0.024 0.214±0.036 8 Comparative Example 5 537±22 0.287±0.023 0.397±0.062 9 Comparative Example 6 542±28 0.474±0.046 0.481±0.094 10 Comparative Example 7 536±25 0.436±0.054 0.445±0.041

[0116] Note 1: Except for the different treatment methods, the other conventional cultivation methods of each group in the table are the same.

[0117] Note 2: According to the requirements of "GB 2762-2022 National Food Safety Standard Limits of Contaminants in Food", the cadmium content of qualified rice should be less than or equal to 0.2 mg / kg, and the arsenic content should be less than or equal to 0.35 mg / kg.

[0118] In summary, the present invention provides a precipitation-loaded coated slow-release carbon-based iron fertilizer and a preparation method thereof. The preparation method is specifically as follows: a biological crustacean heavy metal adsorbent is impregnated with a ferrous sulfate solution, low-temperature dried, and then impregnated with a calcium hydroxide solution again, and finally the dried particles are granulated and coated. This coated slow-release iron fertilizer is loaded by precipitation. Its coating materials, precipitated ferric hydroxide and ferrous hydroxide, and calcium sulfate particles mixed with the precipitate generated simultaneously with the precipitation are uniformly dispersed and attached to the pores of the porous adsorbent to act synergistically. The byproduct calcium sulfate in the porous adsorbent wraps the precipitated ferric hydroxide and ferrous hydroxide, which can achieve long-term slow release of iron ions and reduce soil oxygen content. It is used in combination with the coated iron fertilizer in a precise manner during the seedling raising period. The membrane material can keep the internal material from contacting the outside world during the rice seedling raising period. After the rice seedling raising period, the membrane material loses its effectiveness during the field growth process. At this time, the biological crustacean adsorbent, precipitated ferric hydroxide and ferrous hydroxide, and calcium sulfate particles generated simultaneously with the precipitation and mixed with the precipitate work together to achieve long-term iron ion slow release, and perform iron ion antagonism throughout the rice growth process, reducing the cadmium and arsenic ion absorption of rice. The precipitation-type loading method and the mixed coating of the reaction product calcium sulfate greatly improve the iron ion release law and speed through the adsorption and precipitation effect of the porous material, greatly increase the iron ion release cycle, and perform iron ion antagonism throughout the rice growth process. Compared with traditional slow-release fertilizers, the iron fertilizer of the present invention has excellent The cadmium and arsenic antagonistic effect of the present invention on rice can be greatly reduced with a small amount. In addition, since the present invention is a coated slow-release fertilizer, the coating material remains stable during the rice seedling raising period. After transplanting into the field, the coating structure fails during the critical growth period when rice absorbs a large amount of heavy metals, and the slow-release ferric hydroxide and ferrous hydroxide begin to be released. At this time, if there is too much ferrous sulfate that has not been completely reacted by precipitation reaction in the slow-release material, the ferrous sulfate will quickly enter the soil in a short time and undergo a hydrolysis reaction in the water body, making the soil around the root system acidic, thereby activating the reduced heavy metals in the soil and causing them to transform from the passivated reduced state to the free ionic state. A large amount of heavy metal ions will accumulate around the root system in a short time, and other heavy metal ions in the soil will induce the surface of the rice root system to absorb heavy metals. For example, transport proteins such as cadmium and arsenic ions are reached, resulting in a decrease in the antagonistic effect after the subsequent release of iron ions, and the loss of the advantages of the coated slow-release material. Therefore, when the coated slow-release fertilizer is concentratedly used in the seedling raising matrix during the seedling raising period, its ferrous sulfate content needs to be controlled. Therefore, the present invention impregnates ferrous sulfate in the front and calcium hydroxide in the back, so that the ferrous sulfate is basically completely consumed. The vast majority of the slow-release fertilizer is the by-product calcium sulfate wrapped in precipitated ferric hydroxide and ferrous hydroxide, which can provide iron ion antagonism for a long time. The ferric hydroxide and ferrous hydroxide precipitation is an alkaline precipitation, which can control the soil pH and reduce the mobility of cadmium and arsenic. In addition, since the precipitation is generated in the porous material, there is a covering and wrapping effect of the calcium sulfate particles. While generating the ferric hydroxide precipitation,The ferrous hydroxide precipitate can be retained in part. After being released from the soil, the ferrous hydroxide precipitate can quickly absorb oxygen from the soil, reacting to form ferric hydroxide precipitate. This also consumes oxygen from the soil, reducing the soil oxygen content, reducing the oxygen content in the rice rhizosphere, and reducing the conversion of heavy metals from reduced to oxidized ions. Heavy metal ions in the soil will not be activated. These multiple effects synergize to achieve a better heavy metal antagonistic effect of the coated slow-release material. Furthermore, by precisely sowing a small amount of the coated slow-release material of the present invention in the rice seedling tray during rice seedling cultivation, the coating structure of the slow-release material can be preserved intact for more than 30 days, thereby ensuring the integrity of the slow-release material during rice seedling cultivation and transplanting (or throwing). After rice transplanting (or throwing), the slow-release material is concentrated in the rice rhizosphere at a high concentration in the field and will not be scattered between rice rows. This reduces the loss of slow-release material scattered outside the rice root zone, thereby avoiding ineffective fertilizer application and reducing fertilizer usage. In summary, the invention has excellent application prospects.

[0119] At this point, those skilled in the art will recognize that, although the embodiments of the present invention have been shown and described in detail herein, many other variations or modifications consistent with the principles of the present invention may be directly determined or derived from the disclosure of the present invention without departing from the spirit and scope of the present invention. Therefore, the scope of the present invention should be understood and deemed to cover all such other variations or modifications.

Claims

1. A method for preparing a precipitation-loaded coated slow-release carbon-based iron fertilizer, characterized in that: The preparation method comprises the following steps: Step S1: crushing the biocrust adsorbent into particles with a diameter of no more than 1 mm, impregnating them with FeSO4 solution, filtering them to dryness, and then drying them at low temperature; Step S2: The biological crustacean adsorbent particles dried in step S1 are immersed in a Ca(OH)2 solution, removed from the solution, filtered, and then directly dried at low temperature and crushed into particles with a diameter of no more than 1 mm to obtain iron-based loaded biological crustacean particles; Step S3: using an adhesive, granulating the iron-based loaded biological crustacean particles in step S2 according to a mass ratio, drying at a low temperature, and sieving after drying to obtain a precipitated loaded slow-release carbon-based iron fertilizer; Step S4: preparing a water-based polyacrylate coating, using the precipitated loaded slow-release carbon-based iron fertilizer prepared in step S3 as the fertilizer core, and coating the fertilizer core at a fertilizer core-coating mass ratio of 1:1.0-1.3 to obtain a water-based polyacrylate coated iron fertilizer, that is, a precipitated loaded coated slow-release carbon-based iron fertilizer; The concentration of the Ca(OH)2 solution in step S2 is 5% to 10%; the immersion time is more than 4 hours; the concentration of the FeSO4 solution in step S1 is 5% to 10%; the immersion time is more than 4 hours; The ratio of the concentration of the Ca(OH)2 solution to the concentration of the FeSO4 solution is 1.1-1.5:1; The preparation method of the biological crustacean adsorbent is: Under oxygen-free conditions, the biocrust is treated at a temperature of 300-600° C. for 2-3 hours, and the treated biocrust is modified to obtain a modified biocrust adsorbent; the modification comprises the following steps: Carboxymethylation: reacting the treated biocrust, an alkaline solution, and chloroacetic acid in a mass ratio of 1:(2-4):(1.2-3) to obtain a carboxymethyl biocrust; the alkaline solution is a 10% to 60% NaOH solution; Dialdehydeation: reacting the carboxymethylated biocrust with an oxidant at a mass ratio of 1:(1-2) to obtain a dialdehyde carboxymethylated biocrust; the oxidant is periodic acid and its salts; Schiff base reaction: reacting the dialdehyde carboxymethyl bio-crust with an amino compound at a mass ratio of 1:(1-5) to obtain a dialdehyde carboxymethyl bio-crust Schiff base, which is the bio-crust adsorbent; the amino compound is one or more of aniline, benzylamine, phenylethylamine, m-aminophenol, n-hexylamine, n-octylamine, aminothiazole, m-phenylenediamine, p-phenylenediamine, o-phenylenediamine, aminobenzothiazole, and m-acetylaniline; the bio-crust is one or more of shrimp shell, tortoise shell, crab shell, turtle shell, and fish scale; The specific method for preparing the water-based polyacrylate coating in step S4 is: 8.24 g of nonionic emulsifier polyoxyethylene alkylphenyl ether OP-10, 4.12 g of anionic emulsifier sodium dodecylbenzene sulfonate SDBS and 31 g of hydrolysis inhibitor ethylene glycol EG were dissolved in 248 g of deionized water to prepare an aqueous phase; 110 g of butyl acrylate BA, 90 g of methyl methacrylate MMA and 3.5 g of functional monomer methacrylic acid MAA were mixed to prepare an organic phase; the two phases were stirred at 1000 rpm for 30 min at room temperature using a magnetic stirrer to prepare an oil-water mixture; the polymerization reaction was carried out at 8 The reaction was carried out at 0°C and 400 rpm. 25% of the oil-water mixture was initially added to a three-necked flask. The remaining oil-water mixture and the initiator solution were alternately added to the reaction system four times within 3 hours. After the addition was completed, 5 g of methyl silicone oil was added to the round-bottom flask and the reaction was continued for 3 hours. After the reaction was completed, the heater was turned off. When the temperature dropped to 40°C, the emulsion was filtered through a 100-mesh nylon mesh and then collected. The material was treated three times with a homogenizer at a pressure of 900 bar to obtain a water-based polyacrylate emulsion coating material. The initiator solution was 0.013 g mL -1 of K2S2O8, 52mL.

2. The method for preparing a precipitation-loaded coated slow-release carbon-based iron fertilizer as claimed in claim 1, characterized in that: The volume ratio of the FeSO4 solution to the biological crustacean adsorbent particles in step S1 is 1-1.5:1; the volume ratio of the Ca(OH)2 solution in step S2 to the biological crustacean adsorbent particles dried in step S1 is 1.5-2:

1.

3. The method for preparing a precipitation-loaded coated slow-release carbon-based iron fertilizer as claimed in claim 1, characterized in that: The low-temperature drying temperature in step S1 and step S2 is 55-65°C.

4. The method for preparing a precipitation-loaded coated slow-release carbon-based iron fertilizer as claimed in claim 1, characterized in that: The adhesive comprises one or more of gypsum, quicklime, and slaked lime; water is added for bonding and then granulation is performed, and the amount of water added is 30-40% of the total mass of the adhesive; the mass ratio of the adhesive to the iron-based loaded biological crust particles is 1:3-1:5, and the precipitated loaded coated slow-release carbon-based iron fertilizer in step S3 is filtered through a mesh screen, and the particle size is 2-3 mm.

5. The method for preparing a precipitation-loaded coated slow-release carbon-based iron fertilizer as claimed in claim 4, characterized in that: The mass ratio of the raw gypsum to the iron-based biological crust particles is 1:3, the mass ratio of the quicklime to the iron-based biological crust particles is 1:4, and the mass ratio of the slaked lime to the iron-based biological crust particles is 1:

5.

6. A precipitation-loaded coated slow-release carbon-based iron fertilizer, characterized in that: The iron fertilizer is prepared by the preparation method according to any one of claims 1 to 5.

7. The precise application method of a precipitation-loaded coated slow-release carbon-based iron fertilizer according to claim 6, characterized in that: The application of the precipitated loaded coated slow-release carbon-based iron fertilizer in reducing cadmium ion absorption by rice is as follows: a small amount of the precipitated loaded coated slow-release carbon-based iron fertilizer is applied to the rice seedling raising substrate during the rice seedling raising period; during the seedling raising and transplanting process, the rice root-wrapped seedling raising substrate or the root soil carried by the fertilizer is transferred to the production field together, and no secondary application in the field is required subsequently; the ratio of the seedling raising field area to the transplanting field area is 1:10-1:12.

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