Precipitation load type coated slow-release carbon-based iron fertilizer and preparation method thereof

Abstract

The invention discloses a precipitation-supported coated slow-release carbon-based iron fertilizer and a preparation method thereof.The preparation method specifically comprises the steps that a biological crustacean heavy metal adsorbent is soaked in a ferrous sulfate solution and then soaked in a calcium hydroxide solution again after low-temperature drying, finally, dried particles are granulated and subjected to coating treatment, and the coated slow-release carbon-based iron fertilizer is obtained. The coated slow-release iron fertilizer is loaded in a precipitation mode, a mixture of precipitated ferric hydroxide and ferrous hydroxide is uniformly dispersed and attached to the interiors of pore channels of the porous adsorbent, and the precipitated ferric hydroxide and the ferrous hydroxide are wrapped by a byproduct calcium sulfate in the porous adsorbent, so that long-acting slow release of iron ions can be realized; the rice cadmium arsenic antagonistic iron fertilizer has the advantages that the rice cadmium arsenic antagonistic effect can be achieved, the oxygen content of soil can be reduced, fine quantitative use of the coated iron fertilizer in the seedling raising period is matched, iron ion antagonism and a precipitation type adsorption load mode are carried out in the whole rice growth process, the iron ion release period is greatly prolonged, and the iron fertilizer has the excellent rice cadmium arsenic antagonism effect and has the excellent application prospect.

Description

Technical Field

[0001] The invention relates to the technical field of safe rice production in paddy fields polluted by heavy metals, 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 extensive use of agricultural inputs, the world is facing increasingly serious soil environmental safety issues, among which heavy metal pollution has received the most attention. In 1987, a study by the Lishui Health and Epidemic Prevention Station in Zhejiang Province showed that the cadmium content of rice in the polluted area near the Suichang Gold Mine was seriously exceeded. In 2002, the Ministry of Agriculture's Rice and Product Quality Supervision and Inspection Center conducted a safety sampling test on rice in the national market, and the rice lead exceeded the standard rate by 28.4% and the cadmium exceeded the standard rate by 10.3%. According to the "National Soil Pollution Status Survey Bulletin" jointly issued by the Ministry of Environmental Protection and the Ministry of Land and Resources in 2014, the total soil exceeding the standard rate was 19.4%, of which inorganic pollutants, mainly heavy metals (arsenic, as a metalloid element, is also classified as a heavy metal pollutant because of its similar harm to the human body as heavy metals), accounted for 82.8% of the total number of exceeding the standard. Limited by the current scientific level, heavy metal pollutants that enter the soil cannot be simply and quickly separated from the soil. For the treatment of contaminated soil, the passivation / stabilization method is currently mainly 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] In order to obtain cheap, easy-to-obtain and effective passivation materials, the academic community has conducted a lot of research. However, current passivation materials generally have technical defects such as high cost of passivation agents, insufficient persistence, and large amount of passivation agents. Therefore, it is necessary to design a passivation agent material that can be used to reduce the biological effectiveness of cadmium and arsenic elements in the soil. This material should have long-term effectiveness, that is, long-term antagonism, outstanding passivation effect, etc., and the amount of passivation agent should be greatly reduced, thereby reducing management input 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 for coating treatment. The 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 not only achieve long-term slow release of iron ions, but also can The oxygen content in the soil is reduced, and the coated iron fertilizer is used in a precise manner during the rice seedling raising period, and iron ion antagonism is performed throughout the rice growth process. The precipitation-type adsorption loading method and the coating material greatly increase the release cycle of iron ions. Compared with traditional slow-release fertilizers, the iron fertilizer of the present invention has an excellent antagonistic effect on cadmium and arsenic in rice, and a small amount can greatly 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, 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 reacted completely after precipitation. Ferrous sulfate will quickly enter the soil in large quantities in a short period of time, undergo hydrolysis in the water, and make 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 gather 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 raising base during the seedling raising period. When the ferrous sulfate content is in the soil, it needs to be controlled. Therefore, the present invention impregnates the ferrous sulfate in front and the 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 the precipitated ferric hydroxide and ferrous hydroxide, so that it can provide iron ion antagonism for a long time. The ferric hydroxide and ferrous hydroxide precipitations are alkaline precipitations, 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 and the calcium sulfate particles have a covering and encapsulating effect, a part of the ferrous hydroxide precipitation can be retained while the ferrous hydroxide precipitation is generated. After the ferrous hydroxide precipitation is released in the soil, it can quickly obtain oxygen in the soil, react itself to generate ferric hydroxide precipitation, and also consume oxygen in the soil, so that the soil oxygen content is reduced, the oxygen content in the rhizosphere of rice is reduced, and the ionic transformation of heavy metal reduction state to oxidation state is reduced, and the heavy metal ions in the soil will not be activated. Multiple effects work together to achieve better heavy metal antagonism of the coated slow-release material.At the same time, by precisely sowing the coated slow-release material of the present invention in a small amount in the rice seedling tray during the rice seedling raising period, the coating structure of the slow-release material can be completely preserved for more than 30 days, thereby achieving the integrity of the slow-release material during the rice seedling raising and transplanting (or throwing); after the rice is transplanted (or thrown) in the field, the slow-release material is concentrated in the rice root zone at a high concentration and will not be scattered between the rice rows, reducing the loss of the slow-release material scattered outside the rice root circle, thereby avoiding the ineffective application of fertilizers and reducing the amount of fertilizer used. In summary, it has an excellent application prospect.

[0005] In order to achieve the above technical effects, the following technical solutions are adopted: A method for preparing a precipitation-loaded coated slow-release carbon-based iron fertilizer comprises the following steps: Step S1: crush the biocrust adsorbent into particles with a diameter not greater than 1 mm, impregnate with FeSO4 solution, filter and dry at low temperature; Step S2: The biological crustacean adsorbent particles dried in step S1 are immersed in a Ca(OH)2 solution, taken out, filtered, and directly dried at low temperature and then 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 to granulate the iron-based loaded biological shell 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 by an in-situ melting method, taking the precipitated loaded slow-release carbon-based iron fertilizer in step S3 as the fertilizer core, coating the fertilizer core at a 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.

[0006] Furthermore, in step S1, the concentration of the Ca(OH)2 solution is 5% to 10%; the immersion time is more than 4 hours; in step S2, the concentration of the FeSO4 solution is 5% to 10%; the immersion time is more than 4 hours.

[0007] Furthermore, the specific method for preparing the water-based polyacrylate coating by the in-situ melting method 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 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 with a magnetic stirrer to prepare an oil-water mixture; the polymerization reaction was carried out at 80°C and 400 rpm, and 25% of the oil-water mixture was initially added to a three-necked flask, and the remaining oil-water mixture and 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, and when the temperature dropped to 40°C, the emulsion was passed through 100 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.

[0008] 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 ratio of the volume of the FeSO4 solution to the biological crustacean adsorbent particles in step S1 is 1-1.5:1; the ratio of the volume of the Ca(OH)2 solution in step S2 to the biological crustacean adsorbent particles dried in step S1 is 1.5-2:1; Furthermore, the low-temperature drying temperature is 55-65°C.

[0009] Furthermore, 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 crustacean 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.

[0010] 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.

[0011] Furthermore, the preparation method of the biological crustacean adsorbent is: Under the condition of isolating oxygen, treating the biological shell at a temperature of 300-600° C. for 2-3 hours, and modifying the treated biological shell to obtain the modified biological shell adsorbent; Modification of the treated biocrustacean includes the following steps: Carboxymethylation: reacting the treated biocrust with chloroacetic acid in an alkaline solution to obtain a carboxymethyl 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); Dialdehydeation: reacting carboxymethyl biocarapace with an oxidant to obtain dialdehyde carboxymethyl biocarapace; the oxidant is periodic acid and its salt; the mass ratio of the oxidant to the carboxymethyl biocarapace is (1-2):1; Schiff base reaction: reacting dialdehyde carboxymethyl biological crust 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.

[0012] A precipitation-loaded coated slow-release carbon-based iron fertilizer is prepared by any one of the above preparation methods.

[0013] A precise application method of a precipitated loaded coated slow-release carbon-based iron fertilizer, specifically comprising: applying a small amount of the precipitated loaded coated slow-release carbon-based iron fertilizer into a rice seedling raising substrate during the rice seedling raising period; transferring the rice root-wrapped seedling raising substrate or the root soil carried by the fertilizer to a production field during the rice seedling raising and transplanting process, without the need for subsequent secondary application in the field; the ratio of the rice seedling raising field area to the transplanting field area is 1:10-1:12; applying the loaded coated slow-release carbon-based iron fertilizer during the rice seedling raising process and bringing it into the field during the transplanting process can actually significantly reduce the field usage of the coated slow-release carbon-based iron fertilizer and reduce the labor input for spreading.

[0014] The beneficial effects of the present invention are: 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 at a low temperature, and then impregnating the mixture with a calcium hydroxide solution; finally, drying the obtained particles, granulating the particles, and performing coating treatment; the coated slow-release iron fertilizer is loaded by precipitation; the coating materials, precipitated ferric hydroxide and ferrous hydroxide, and calcium sulfate particles generated simultaneously with the precipitation and mixed with the precipitated particles 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 coated material is used in a precise manner during the rice seedling raising period. During the seedling period, the internal materials can be kept from contacting the outside world. After the seedling period is over, during the field growth process, the coating material becomes ineffective. 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 in the precipitation work together to achieve long-term slow release of iron ions, and perform iron ion antagonism throughout the whole process of rice growth, thereby reducing the absorption of cadmium and arsenic ions by rice. The precipitation-type loading method and the mixed packaging of the reaction product calcium sulfate greatly improve the iron ion release law and speed through the adsorption and precipitation of porous materials, greatly increase the iron ion release cycle, and perform iron ion antagonism throughout the whole process of rice growth. 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 reacted completely 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 converting them from the passivated reduced state to the free ionic state. A large amount of heavy metal ions gather 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 reduction in the 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 ferric hydroxide and ferrous hydroxide, which are precipitated by the byproduct calcium sulfate, thereby providing 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 calcium sulfate particles, a portion of the ferrous hydroxide precipitate can be retained while the ferric hydroxide precipitate is generated.After the ferrous hydroxide precipitate is released in the soil, it can quickly obtain oxygen in the soil, react itself to generate ferric hydroxide precipitate, and also consume oxygen in the soil, so that the soil oxygen content is reduced, the oxygen content in the rice rhizosphere is reduced, and the ionic transformation of heavy metal reduction to oxidation state is reduced, and the heavy metal ions in the soil are not activated. Multiple effects work together to achieve 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 completely preserved 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 materials scattered outside the rice root circle, thereby avoiding ineffective application of fertilizers and reducing fertilizer usage. In summary, it has excellent application prospects. , BRIEF DESCRIPTION OF THE DRAWINGS

[0015] 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; 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

[0016] The present invention is further described below in conjunction with the accompanying drawings, and the protection scope of the present invention is not limited to the following: 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.

[0017] Embodiment 1: In this embodiment, the preparation method of the biological crustacean adsorbent is: The biological crustaceans were treated at 300°C for 2h under oxygen-free conditions; Modifying the treated biological crust to obtain the modified biological crust adsorbent comprises the following steps: Carboxymethylation: reacting the treated biocrust with chloroacetic acid in an alkaline solution to obtain a carboxymethyl biocrust; the alkaline solution is a 10% NaOH solution; the mass ratio of the treated biocrust: alkali: chloroacetic acid is 1:2:1.2; 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; Schiff base reaction: reacting dialdehyde carboxymethyl biological crust 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 a shrimp shell.

[0018] A method for preparing a precipitation-loaded coated slow-release carbon-based iron fertilizer in this embodiment is as follows, comprising the following steps: Step S1: crush the biological crustacean adsorbent into particles with a diameter not greater than 1 mm, impregnate with FeSO4 solution, filter and dry at low temperature at 55°C; the concentration of FeSO4 solution is 5%; the impregnation time is more than 4 hours; the volume ratio of FeSO4 solution to biological crustacean adsorbent particles is 1:1; Step S2: The biological shell adsorbent particles dried in step S1 are immersed in a Ca(OH)2 solution, and after being taken out and filtered, they are 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 shell 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 shell adsorbent particles dried in step S1 is 1.5:1; Step S3: using an adhesive, the adhesive includes raw gypsum, quicklime, and slaked lime; the mass ratio of raw 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, drying at low temperature, the temperature is 50°C, and sieving after drying to obtain a precipitated loaded slow-release carbon-based iron fertilizer.

[0019] Step S4: preparing a water-based polyacrylate coating by an in-situ melting method, the specific method is as follows: 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 with a magnetic stirrer to prepare an oil-water mixture; the polymerization reaction was carried out at 80°C and 400 rpm, and 25% of the oil-water mixture was initially added to a three-necked flask, and the remaining oil-water mixture and 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, and when the temperature dropped to 40°C, the emulsion was passed through 100 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.

[0020] 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 obtain a water-based polyacrylate coated iron fertilizer, that is, a precipitated loaded coated slow-release carbon-based iron fertilizer 1.

[0021] Embodiment 2: In this embodiment, the preparation method of the biological crustacean adsorbent is: The biological carapace was treated at 600°C for 3h under oxygen-free conditions; Modifying the treated biological crust to obtain the modified biological crust adsorbent comprises the following steps: Carboxymethylation: reacting the treated biocrust with chloroacetic acid in an alkaline solution to obtain a carboxymethyl biocrust; the alkaline solution is a 60% NaOH solution; the mass ratio of the treated biocrust: alkali: chloroacetic acid is 1:4:3; 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; Schiff base reaction: react dialdehyde carboxymethyl biological crust 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 a crab shell.

[0022] A method for preparing a precipitation-loaded coated slow-release carbon-based iron fertilizer in this embodiment is as follows, comprising the following steps: Step S1: crush the biological crustacean adsorbent into particles with a diameter of no more than 1 mm, impregnate with FeSO4 solution, filter and dry at low temperature, the temperature is 65°C; the concentration of FeSO4 solution is 6.67%; the impregnation time is more than 4 hours; the volume ratio of FeSO4 solution to biological crustacean adsorbent particles is 1.5:1; Step S2: The biological crustacean adsorbent particles dried in step S1 are immersed in a Ca(OH)2 solution, and after being taken out and filtered, they are 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; Step S3: using an adhesive, the adhesive includes raw gypsum, quicklime, and slaked lime; the mass ratio of raw 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, drying at a low temperature of 55°C, and sieving after drying to obtain a precipitated loaded slow-release carbon-based iron fertilizer.

[0023] Step S4: preparing a water-based polyacrylate coating by an in-situ melting method, the specific method is as follows: 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 with a magnetic stirrer to prepare an oil-water mixture; the polymerization reaction was carried out at 80°C and 400 rpm, and 25% of the oil-water mixture was initially added to a three-necked flask, and the remaining oil-water mixture and 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, and when the temperature dropped to 40°C, the emulsion was passed through 100 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.

[0024] The precipitated loaded slow-release carbon-based iron fertilizer in step S3 is used as the fertilizer core, and the fertilizer core is coated at a fertilizer core coating mass ratio of 1: 1.3 to obtain a water-based polyacrylate coated iron fertilizer, thereby obtaining a precipitated loaded coated slow-release carbon-based iron fertilizer 2.

[0025] Comparative Example 1: Based on Example 1: In this comparative example, the preparation method of the biological crustacean adsorbent is consistent with that in Example 1.

[0026] The preparation method of a common loaded slow-release carbon-based iron fertilizer in this comparative example is as follows, comprising the following steps: Step S1: crush the biological crustacean adsorbent into particles with a diameter not greater than 1 mm, immerse in FeSO4 solution, remove and filter, directly dry at low temperature, and then crush into particles with a diameter not greater than 1 mm at a temperature of 55°C to obtain iron-based loaded biological crustacean particles; the concentration of FeSO4 solution is 5%; the immersion time is more than 4 hours; the volume ratio of FeSO4 solution to biological crustacean adsorbent particles is 1:1; Step S2: using an adhesive, the adhesive includes raw gypsum, quicklime, and slaked lime; the mass ratio of raw 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 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.

[0027] Step S3: preparing a water-based polyacrylate coating by an in-situ melting method, the specific method is as follows: 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 with a magnetic stirrer to prepare an oil-water mixture; the polymerization reaction was carried out at 80°C and 400 rpm, and 25% of the oil-water mixture was initially added to a three-necked flask, and the remaining oil-water mixture and 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, and when the temperature dropped to 40°C, the emulsion was passed through 100 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.

[0028] 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 obtained by coating the fertilizer core at a mass ratio of 1:1, thereby obtaining the ordinary loaded coated slow-release carbon-based iron fertilizer 3.

[0029] Comparative Example 2: Based on Example 1: In this comparative example, the preparation method of the biological crustacean adsorbent is consistent with that in Example 1.

[0030] The preparation method of a common loaded slow-release carbon-based iron fertilizer in this comparative example is as follows, comprising the following steps: Step S1: crush the biological crustacean adsorbent into particles with a diameter not greater than 1 mm, immerse in a Ca(OH)2 solution, remove and filter, and then directly dry at low temperature and crush into particles with a diameter not greater than 1 mm at a temperature of 55°C to obtain 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 is 1.5:1; Step S2: using an adhesive, the adhesive includes 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.

[0031] Step S3: preparing a water-based polyacrylate coating by an in-situ melting method, the specific method is as follows: 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 with a magnetic stirrer to prepare an oil-water mixture; the polymerization reaction was carried out at 80°C and 400 rpm, and 25% of the oil-water mixture was initially added to a three-necked flask, and the remaining oil-water mixture and 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, and when the temperature dropped to 40°C, the emulsion was passed through 100 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.

[0032] The ordinary loaded slow-release carbon-based iron fertilizer in step S2 is used as the fertilizer core, and the fertilizer core is coated at a fertilizer core coating mass ratio of 1:1 to obtain a water-based polyacrylate coated fertilizer, that is, an ordinary loaded coated slow-release carbon-based fertilizer 4.

[0033] Comparative Example 3: In this comparative example, the preparation method of the biological crustacean adsorbent is consistent with that in Example 1.

[0034] The preparation method of a common loaded slow-release carbon-based iron fertilizer in this comparative example is as follows, comprising the following steps: Step S1: loading with iron hydroxide powder: crush the biological crustacean adsorbent into particles with a diameter of no more than 1 mm, take 3 parts by weight of the biological crustacean adsorbent particles and 8 parts by weight of the iron hydroxide powder, mix the biological crustacean adsorbent particles and the iron hydroxide powder evenly, add them into a shaking device for shaking, and after the shaking is completed, use a screening device to separate the biological crustacean adsorbent particles loaded with iron hydroxide powder for later use; Step S2: using an adhesive, the adhesive includes raw gypsum, quicklime, and slaked lime; the mass ratio of raw gypsum to the biological shell adsorbent particles loaded with iron hydroxide powder is 1:3, the mass ratio of quicklime to the biological shell adsorbent particles loaded with iron hydroxide powder is 1:4, and the mass ratio of slaked lime to the biological shell 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 shell adsorbent particles loaded with iron hydroxide powder in step S1 according to the mass ratio, low-temperature drying at a temperature of 50°C, and sieving after drying to obtain a common loaded slow-release carbon-based iron fertilizer.

[0035] Step S3: preparing a water-based polyacrylate coating by an in-situ melting method, the specific method is as follows: 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 with a magnetic stirrer to prepare an oil-water mixture; the polymerization reaction was carried out at 80°C and 400 rpm, and 25% of the oil-water mixture was initially added to a three-necked flask, and the remaining oil-water mixture and 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, and when the temperature dropped to 40°C, the emulsion was passed through 100 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.

[0036] The ordinary loaded slow-release carbon-based iron fertilizer in step S2 is used as the fertilizer core, and the fertilizer core is coated at a fertilizer core coating mass ratio of 1: 1 to obtain a water-based polyacrylate coated iron fertilizer, that is, an ordinary loaded coated slow-release carbon-based iron fertilizer 5.

[0037] Comparative Example 4: In this comparative example, the preparation method of the biological crustacean adsorbent is consistent with that in Example 1.

[0038] The preparation method of a precipitated loaded slow-release carbon-based iron fertilizer of this comparative example is as follows, comprising the following steps: Step S1: crush the biological crustacean adsorbent into particles with a diameter not greater than 1 mm, soak them in a Ca(OH)2 solution, filter and dry them at a low temperature at 55°C; the concentration of the Ca(OH)2 solution is 5%; the soaking time is more than 4 hours; the volume ratio of the Ca(OH)2 solution to the biological crustacean adsorbent particles is 1:1; Step S2: The biological crustacean adsorbent particles dried in step S1 are immersed in a FeSO4 solution, taken out 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 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; Step S3: using an adhesive, the adhesive includes raw gypsum, quicklime, and slaked lime; the mass ratio of raw gypsum to iron-based biological shell particles with a slight excess of ferrous sulfate is 1:3, the mass ratio of quicklime to iron-based biological shell particles with a slight excess of ferrous sulfate is 1:4, and the mass ratio of slaked lime to iron-based biological shell particles with a slight excess of ferrous sulfate 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 biological shell particles with a slight excess of ferrous sulfate in step S2 according to the mass ratio, low-temperature drying at a temperature of 50°C, sieving after drying, and the particle size is 2 mm; obtaining a precipitation-loaded slow-release carbon-based iron fertilizer; Step S5: preparing a water-based polyacrylate coating by an in-situ melting method, the specific method is as follows: 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 with a magnetic stirrer to prepare an oil-water mixture; the polymerization reaction was carried out at 80°C and 400 rpm, and 25% of the oil-water mixture was initially added to a three-necked flask, and the remaining oil-water mixture and 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, and when the temperature dropped to 40°C, the emulsion was passed through 100 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.

[0039] The precipitated loaded slow-release carbon-based iron fertilizer in step S3 is used as the fertilizer core, and the fertilizer core is coated at a fertilizer core coating mass ratio of 1:1 to obtain a water-based polyacrylate coated iron fertilizer, thereby obtaining a precipitated loaded coated slow-release carbon-based iron fertilizer 6.

[0040] Comparative Example 5: In this comparative example, the preparation method of the biological crustacean adsorbent is consistent with that in Example 1.

[0041] The preparation method of a precipitated loaded slow-release carbon-based iron fertilizer of this comparative example is as follows, comprising the following steps: Step S1: crush the biological crustacean adsorbent into particles with a diameter not greater than 1 mm, soak them in a Ca(OH)2 solution, filter and dry them at a low temperature at 55°C; the concentration of the Ca(OH)2 solution is 5%; the soaking time is more than 4 hours; the volume ratio of the Ca(OH)2 solution to the biological crustacean adsorbent particles is 1:1; Step S2: The biological crustacean adsorbent particles dried in step S1 are immersed in a FeSO4 solution, taken out 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 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; Step S3: The iron-based biological crustacean particles dried in step S2 are immersed in the FeSO4 solution again, and after being fished out and filtered, they are directly dried at low temperature and crushed into particles with a diameter not greater than 1 mm at a temperature of 55°C to obtain iron-based biological crustacean 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 crustacean adsorbent particles dried in step S2 is 1:1.

[0042] Step S4: using an adhesive, the adhesive includes gypsum, quicklime, and slaked lime; the mass ratio of gypsum to iron-based biological shell particles with excess ferrous sulfate is 1:3, the mass ratio of quicklime to iron-based biological shell particles with excess ferrous sulfate is 1:4, and the mass ratio of slaked lime to iron-based biological shell particles with excess ferrous sulfate 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 biological shell particles with excess ferrous sulfate in step S3 according to the mass ratio, drying at low temperature, the temperature is 50°C, and sieving after drying, the particle size is 2 mm; obtaining a precipitation-loaded slow-release carbon-based iron fertilizer; Step S5: preparing a water-based polyacrylate coating by an in-situ melting method, the specific method is as follows: 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 with a magnetic stirrer to prepare an oil-water mixture; the polymerization reaction was carried out at 80°C and 400 rpm, and 25% of the oil-water mixture was initially added to a three-necked flask, and the remaining oil-water mixture and 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, and when the temperature dropped to 40°C, the emulsion was passed through 100 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.

[0043] The precipitated loaded slow-release carbon-based iron fertilizer in step S4 is used as the fertilizer core, and the fertilizer core is coated at a fertilizer core coating mass ratio of 1:1 to obtain a water-based polyacrylate coated iron fertilizer, namely, a precipitated loaded coated slow-release carbon-based iron fertilizer 7.

[0044] Comparative Example 6: In this comparative example, the preparation method of the biological crustacean adsorbent is consistent with 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.

[0045] Comparative Example 7: In this comparative example, the preparation method of the biological crustacean adsorbent is consistent with 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 a precipitation-loaded coated slow-release carbon-based iron fertilizer 9.

[0046] The slow-release carbon-based iron fertilizers in Examples 1-2 and Comparative Examples 1-7 are evaluated below: The experiment was conducted in a paddy field with a pH of 5.33, total cadmium of 0.71 mg / kg, total arsenic of 53 mg / kg, and 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 a blank control group CK (no slow-release carbon-based iron fertilizer passivator was applied), and treatment areas 2-10 were the slow-release carbon-based iron fertilizer passivators in Examples 1-2 and Comparative Examples 1-7, respectively; the same rice variety was planted in all of them, namely Taiyou 398.

[0047] Rice seedlings are raised in the field or in mechanized seedling trays. During the preparation of rice seedling trays, a total of 9 slow-release carbon-based iron fertilizer passivators in Examples 1-2 and Comparative Examples 1-7 (3 plots for each slow-release carbon-based iron fertilizer passivator) are evenly applied to the seedling trays at a seedling field dosage of 30 kg / mu (the ratio of the seedling field to the transplanting field area is 1:10, and the actual field dosage is 3 kg / mu), and the seedling soil is covered. The application effect is as follows: Figure 1 and Figure 2 As shown. A control treatment CK was also set up. No slow-release carbon-based iron fertilizer passivator was used in the control treatment during the seedling raising process (3 plots). The germinated rice seeds were evenly sown in the seedling trays and transplanted after about 20 days of seedling raising.

[0048] Two days before rice transplanting, apply compound fertilizer (total nutrient content 45%, of which N-P2O5-K2O=15-15-15) 45kg / mu, transplant rice seedlings by throwing (under paddy field seedling raising conditions) or mechanical transplanting (under mechanized seedling raising conditions), and carry root soil or seedling raising substrate for transplanting. Apply 8kg / mu of urea during the rice tillering period. Other field water and fertilizer management methods and pest and disease control methods are consistent with traditional methods. After the rice matures, harvest and measure the yield of each plot, and measure the cadmium and arsenic content in the rice.

[0049] The determination method of cadmium and arsenic content in brown rice is as follows: take 0.1g brown rice powder sample, add 5mL nitric acid and 3.0mL hydrogen peroxide solution, cover and cold digest overnight, digest for 2h using graphite digester and dilute to 25mL, and analyze and determine the cadmium and arsenic concentrations in the digestion solution using inductively coupled plasma mass spectrometry. The test results are shown in Table 1.

[0050] Table 1 Differences in rice yield and cadmium and arsenic contents in brown rice among treatments 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 Note 1: Except for the different treatment methods, the other conventional cultivation methods of each group in the table are the same.

[0051] 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.

[0052] 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 for coating treatment. This 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 to synergistically act. The byproduct calcium sulfate in the porous adsorbent wraps the precipitated ferric hydroxide and ferrous hydroxide, which can not only achieve long-term slow release of iron ions, but also reduce the oxygen content in the soil. 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 materials from contacting the outside world during the rice seedling raising period. After the rice seedling raising period is over, during the field growth process, the coating material becomes ineffective. 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 whole process of rice growth, reduce the absorption of cadmium and arsenic ions by rice, and 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, perform iron ion antagonism throughout the whole process of rice growth, and compared with traditional slow-release fertilizers, the iron fertilizer of the present invention has excellent The cadmium and arsenic antagonism of rice can be achieved with a relatively small amount of fertilizer, and the cadmium content of rice can be greatly reduced. In addition, since the invention is a coated slow-release fertilizer, the coating material of the invention remains stable during the rice seedling raising period, and 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 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 transforming them from the passivated reduced state to the free ionic state. A large amount of heavy metal ions gather 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, the transport proteins such as cadmium and arsenic ions are reached, resulting in a decrease in the antagonistic effect of 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 consumed. The vast majority of the slow-release fertilizer is ferric hydroxide and ferrous hydroxide, which are precipitated by the by-product calcium sulfate, thereby providing iron ion antagonism for a long time. The ferric hydroxide and ferrous hydroxide precipitations are alkaline precipitations, 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, there is a covering and wrapping effect of calcium sulfate particles. While generating the ferric hydroxide precipitation,It can retain a part of the ferrous hydroxide precipitate. After the ferrous hydroxide precipitate is released in the soil, it can quickly obtain oxygen in the soil, react itself to generate ferric hydroxide precipitate, and also consume oxygen in the soil, so that the soil oxygen content is reduced, the oxygen content in the rice rhizosphere is reduced, and the ionic transformation of heavy metal reduction to oxidation state is reduced, and the heavy metal ions in the soil will not be activated. Multiple effects work together to achieve better heavy metal antagonism of the coated slow-release material. At the same time, by accurately sowing the coated slow-release material of the present invention in a small amount in the rice seedling tray during rice seedling cultivation, the coating structure of the slow-release material can be completely preserved 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 materials scattered outside the rice root circle, thereby avoiding ineffective application of fertilizers and reducing fertilizer usage. In summary, it has excellent application prospects. ,

[0053] At this point, those skilled in the art recognize that, although the embodiments of the present invention have been shown and described in detail herein, many other variations or modifications that conform to the principles of the present invention can still be directly determined or derived based on the contents disclosed in 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 recognized as covering 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: crush the biocrust adsorbent into particles with a diameter not greater than 1 mm, impregnate with FeSO4 solution, filter and dry at low temperature; Step S2: The biological crustacean adsorbent particles dried in step S1 are immersed in a Ca(OH)2 solution, taken out, filtered, and directly dried at low temperature and then 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 to granulate the iron-based loaded biological shell 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 by an in-situ melting method, taking the precipitated loaded slow-release carbon-based iron fertilizer in step S3 as the fertilizer core, coating the fertilizer core at a 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.

2. A method for preparing a precipitation-loaded coated slow-release carbon-based iron fertilizer as described in claim 1, characterized in that: In step S1, the concentration of the Ca(OH)2 solution is 5% to 10%; the immersion time is more than 4 hours; in step S2, the concentration of the FeSO4 solution is 5% to 10%; the immersion time is more than 4 hours.

3. A method for preparing a precipitation-loaded coated slow-release carbon-based iron fertilizer as described in claim 1, characterized in that: The specific method for preparing the water-based polyacrylate coating by the in-situ melting method 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 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 with a magnetic stirrer to prepare an oil-water mixture; the polymerization reaction was carried out at 80°C and 400 rpm, and 25% of the oil-water mixture was initially added to a three-necked flask, and the remaining oil-water mixture and initiator solution were added to the reaction system alternately 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, and when the temperature dropped to 40°C, the emulsion was passed through 100 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.

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

1.

5. A method for preparing a precipitation-loaded coated slow-release carbon-based iron fertilizer as described in claim 1, characterized in that: The low-temperature drying temperature is 55-65°C.

6. A 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 shell 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.

7. A method for preparing a precipitation-loaded coated slow-release carbon-based iron fertilizer as claimed in claim 6, 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.

8. The method for preparing a precipitation-loaded coated slow-release carbon-based iron fertilizer as claimed in claim 1, characterized in that: The preparation method of the biological crustacean adsorbent is: Under the condition of isolating oxygen, treating the biological shell at a temperature of 300-600° C. for 2-3 hours, and modifying the treated biological shell to obtain the modified biological shell adsorbent; Modification of the treated biocrustacean includes the following steps: Carboxymethylation: reacting the treated biocrust with chloroacetic acid in an alkaline solution to obtain a carboxymethyl 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); Dialdehydeation: reacting carboxymethyl biocarapace with an oxidant to obtain dialdehyde carboxymethyl biocarapace; the oxidant is periodic acid and its salt; the mass ratio of the oxidant to the carboxymethyl biocarapace is (1-2):1; Schiff base reaction: reacting dialdehyde carboxymethyl biological crust 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.

9. 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 8.

10. The precise application method of a precipitation-loaded coated slow-release carbon-based iron fertilizer according to claim 8, characterized in that: The application of the precipitated loaded coated slow-release carbon-based iron fertilizer in reducing cadmium ion absorption of rice is specifically 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, and the rice seedling raising substrate or the root soil carried is transferred to the production field during the seedling raising and transplanting process, 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; the loaded coated slow-release carbon-based iron fertilizer is applied during the rice seedling raising process and enters the field with the transplanting process, which can actually greatly reduce the field usage of the coated slow-release carbon-based iron fertilizer and reduce the labor input for spreading.

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