A precipitation-loaded alkaline coated slow-release carbon-based iron fertilizer, preparation method and precise application method thereof

Abstract

The invention discloses a precipitation-loaded alkaline coated slow-release carbon-based iron fertilizer, a preparation method and a precise application method thereof. The coated slow-release iron fertilizer is loaded by an impregnation precipitation method, wherein a precipitated mixture of ferric hydroxide and ferrous hydroxide and a slightly excessive amount of ferric sulfate are uniformly dispersed and attached to a porous adsorbent, and the byproduct calcium sulfate in the adsorbent coats the ferric hydroxide and ferrous hydroxide to achieve long-term slow-release of iron ions. The slightly excessive amount of ferric sulfate can quickly provide iron ions in the early growth stage of rice to antagonize the absorption of cadmium and arsenic ions, and the alkaline coating can antagonize the acidity of water caused by the slightly excessive amount of ferric sulfate. When the coated iron fertilizer is used in a precise manner during the rice seedling raising period, iron ion antagonism is performed throughout the entire rice growth process, and the precipitation-type adsorption loading method greatly prolongs the release period of the iron ions. The iron fertilizer of the invention has an excellent cadmium and arsenic antagonistic effect on rice, can greatly reduce the cadmium and arsenic content of rice with a small amount of use, 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 alkaline-coated slow-release carbon-based iron fertilizer, a preparation method and a precise application method thereof. Background Art

[0002] In recent years, with the development of industry and the extensive use of agricultural inputs, the world has faced increasingly serious soil environmental safety issues, with heavy metal pollution receiving particular attention. 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 at a rate of 19.4%. Of these, 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), accounted for 82.8% of the total number of exceedances. Limited by current scientific knowledge, heavy metal contaminants that enter the soil cannot be easily and quickly isolated. The main method currently used to remediate contaminated soil is passivation / stabilization. This approach, rather than reducing the total amount of heavy metals in the soil, uses technical means to reduce the mobility and bioavailability of pollutants, thereby curbing their impact and ecological risks, reducing the uptake of heavy metals by crops like rice, and ensuring safe agricultural production.

[0003] Currently, passivation materials usually use chemical antagonism, physical adsorption and other methods to deactivate heavy metals in the soil, with the aim of reducing the absorption of heavy metals by crops such as rice. Chemical antagonism usually uses metal ions with a similar structure to heavy metals to antagonize, so that crops absorb antagonistic ions instead of heavy metal ions, thereby reducing crop absorption; physical adsorption adds porous adsorption materials to the soil to adsorb heavy metal ions in the pores, increasing the difficulty of crops to absorb heavy metals, thereby achieving the purpose of reducing the concentration of heavy metals in rice. Some studies use a variety of composite materials to strengthen the two composite effects to reduce the mobility of heavy metals. However, the compound alkaline heavy metal passivation materials currently used in the industry are usually used in amounts of 100-300kg / mu, which is a large amount and has poor long-term effectiveness. They need to be used all year round, which increases the cost of treatment.

[0004] In view of this, the present invention can overcome the technical defects of the existing technology such as high cost of passivators, insufficient persistence, and large amount of passivators. Through antagonism and physical adsorption, the passivator material can reduce the biological effectiveness of cadmium and arsenic elements in the soil. This material should have long-term effectiveness, that is, long-term antagonism, and outstanding passivation effect. Summary of the Invention

[0005] The object of the present invention is to overcome the shortcomings of the prior art and provide a precipitation-loaded alkaline coated slow-release carbon-based iron fertilizer, a preparation method and a precise application method thereof. The preparation method is specifically as follows: a biological crustacean heavy metal adsorbent is impregnated with a calcium hydroxide solution, low-temperature drying is performed, and then the ferrous sulfate solution is impregnated again. The particles obtained by drying are granulated and then alkaline coated. This coated slow-release iron fertilizer is loaded by precipitation, and the precipitated ferric hydroxide, ferrous hydroxide and slightly excess ferric sulfate 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 reduce soil oxygen content. The slightly excess ferric sulfate can quickly provide iron ions in the early stage of rice growth. Antagonize the absorption of cadmium and arsenic ions; cooperate with the precise use of coated iron fertilizer in 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 improve the release cycle of iron ions. Compared with traditional slow-release fertilizers, the iron fertilizer of the present invention has excellent cadmium and arsenic antagonism of rice, and a smaller amount can greatly reduce the cadmium content of 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 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 a large amount of ferrous sulfate is present in the slow-release material, the ferrous sulfate will quickly enter the soil near the root system in a short time and undergo hydrolysis reaction in the water body. The soil around the roots becomes acidic, thereby activating the reduced heavy metals in the soil and transforming them from the passivated reduced state to the free ionic state. In a short period of time, a large number of heavy metal ions gather around the roots. 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 after the subsequent release of iron ions, and losing the advantage of the coated slow-release material. However, if ferrous sulfate is impregnated first and calcium hydroxide is impregnated later, the ferrous sulfate will be almost completely consumed. The vast majority of the slow-release fertilizer is ferric hydroxide, without ferrous sulfate. Before the ferric hydroxide is released, there is no iron ion to antagonize. Other heavy metal ions in the soil will induce the rice roots to express transport proteins such as cadmium and arsenic ions, paving the way for the subsequent iron ion antagonism. Manufacturing obstacles, therefore, in the present invention, calcium hydroxide is impregnated in the front and ferrous sulfate is impregnated once in the back, so that most of the ferrous sulfate is converted into ferric hydroxide precipitation load, but a small amount of ferrous sulfate will remain in the pores of the porous material. This part of ferrous sulfate can quickly enter the soil when the coating fails, and can quickly provide iron ions to antagonize the absorption of cadmium and arsenic ions in the early stage of rice growth. On the one hand, the content of ferrous sulfate is relatively small at this time, which is not enough to cause strong acidity of the water body, and the alkaline coating of the present invention will also consume the acidic environment in the soil before it fails in the field, neutralizing the acidity enhancement brought by ferrous sulfate. On the other hand, the alkaline coating, alkaline adhesive and alkaline precipitated ferric hydroxide and ferrous hydroxide of the present invention, due to their alkalinity, will reduce soil acidity in the field.This can passivate the reduced heavy metals in the soil and reduce the mobility of cadmium and arsenic. In addition, since the precipitation is generated in the porous material and is covered by the calcium sulfate particles, a portion of the ferrous hydroxide precipitation can be retained while the ferric hydroxide precipitation is generated. 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, and reducing the conversion of heavy metal reduced state to oxidized ionic state. It will not activate the heavy metal ions in the soil, causing them to convert from free ionic state to passivated reduced state, passivating and fixing the heavy metals around the soil roots. In this environment, a small amount of excess ferrous sulfate in the early stage provides antagonism in the early stage of rice growth. The precipitated ferric hydroxide and ferrous hydroxide are mixed and wrapped by the by-product calcium sulfate and evenly dispersed and attached to the pores of the porous adsorbent. The precipitated ferric hydroxide and ferrous hydroxide can achieve long-term iron ion slow release, and perform iron ion antagonism throughout the entire process of rice growth. The alkaline coating, alkaline adhesive and alkaline precipitated ferric hydroxide and ferrous hydroxide can antagonize the hydrolysis acidity of slightly excess ferrous sulfate and provide an alkaline soil environment. The synergistic effect of the above conditions achieves better heavy metal antagonism of the coated slow-release material. At the same time, by precisely spreading 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) in the field, the slow-release material is concentrated in the rice rhizosphere at a high concentration 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. It has excellent application prospects.

[0006] In order to achieve the above technical effects, the following technical solutions are adopted:

[0007] A method for preparing a precipitation-loaded alkaline coated slow-release carbon-based iron fertilizer comprises the following steps:

[0008] Step S1: crush the biocrust adsorbent into particles with a diameter of no more than 1 mm, impregnate with Ca(OH)2 solution, filter dry, and dry at low temperature;

[0009] Step S2: The biocrust adsorbent particles dried in step S1 are immersed in a FeSO4 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 biocrust particles with a slightly excess of ferrous sulfate;

[0010] Step S3: using an adhesive, granulating the iron-based loaded biological shell particles with a slightly excess of ferrous sulfate in step S2 according to a mass ratio, drying at low temperature, and sieving after drying to obtain a precipitated loaded slow-release carbon-based iron fertilizer;

[0011] Step S4: At room temperature, an alkaline material is used as a coating, wherein the alkaline material is one or both of quicklime and slaked lime. The precipitated loaded slow-release carbon-based iron fertilizer in step S3 is used as the fertilizer core, and the precipitated loaded slow-release carbon-based iron fertilizer and the coating material are added to a granulator according to a mass ratio. Saturated sodium carbonate or saturated sodium bicarbonate aqueous solution is sprayed in small amounts and multiple times, and the amount of saturated sodium carbonate or saturated sodium bicarbonate solution added is 15-20% of the total mass of the precipitated loaded slow-release carbon-based iron fertilizer and the alkaline material coating; the precipitated loaded slow-release carbon-based iron fertilizer is coated, dried at low temperature until the outer surface is dry, and sieved after drying to a particle size of 4-5 mm; the prepared coating material is fully hardened at room temperature; and the precipitated loaded alkaline coated slow-release carbon-based iron fertilizer is obtained.

[0012] 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.

[0013] Furthermore, the mass ratio of the coating material to the precipitated loaded slow-release carbon-based iron fertilizer in step S4 is 1:1-1:3; the drying temperature after coating is 40-45° C.; and the sufficient hardening time at room temperature is not less than 48 hours.

[0014] Furthermore, the ratio of the concentration of the FeSO4 solution to the concentration of the Ca(OH)2 solution is 1.1~1.5:1, the ratio of the volume of the Ca(OH)2 solution to the biological crust adsorbent particles in step S1 is 1~1.5:1; and the ratio of the volume of the FeSO4 solution in step S2 to the biological crust 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 granulated, 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 with a slightly excess of ferrous sulfate is 1:3~1:5, and the preparation method of the precipitation-loaded slow-release carbon-based iron fertilizer in step S3 is filtered through a mesh, and the particle size is 2~3 mm.

[0017] Furthermore, the mass ratio of the raw gypsum to the iron-based biological crust particles with a slightly excess of ferrous sulfate is 1:3, the mass ratio of the quicklime to the iron-based biological crust particles with a slightly excess of ferrous sulfate is 1:4, and the mass ratio of the slaked lime to the iron-based biological crust particles with a slightly excess of ferrous sulfate 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 alkaline 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 alkaline coated slow-release carbon-based iron fertilizer comprises the following steps: a small amount of the precipitated alkaline coated slow-release carbon-based iron fertilizer is applied to a rice seedling raising substrate during the rice seedling raising period; during the rice seedling raising and transplanting process, the rice root-wrapped seedling raising substrate or the root soil carried by the fertilizer is transferred to a production field, and no secondary application in the field is required; and the ratio of the rice seedling raising field area to the transplanting field area is 1:10-1:15.

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

[0027] The invention provides a precipitation-loaded alkaline coated slow-release carbon-based iron fertilizer, a preparation method and a precise application method thereof. The preparation method specifically comprises the following steps: impregnating a biological crustacean heavy metal adsorbent with a calcium hydroxide solution, drying at a low temperature, and then impregnating the mixture with a ferrous sulfate solution again. The particles obtained by drying are granulated and then alkaline coated. The coated slow-release iron fertilizer is loaded by precipitation, and the precipitated ferric hydroxide, ferrous hydroxide and slightly excessive ferric sulfate are uniformly dispersed and attached to the pores of the 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 slightly excessive ferric sulfate can quickly provide iron ions to antagonize the absorption of cadmium and arsenic ions in the early stage of rice growth. The precise use of iron fertilizer during the rice seedling raising period performs iron ion antagonism throughout the rice growth process. The precipitation-type adsorption loading method and coating material greatly increase the release cycle of iron ions. Compared with traditional slow-release fertilizers, the iron fertilizer of the present invention has excellent cadmium and arsenic antagonism against rice, and a smaller dosage can greatly reduce the cadmium content of 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 a large amount of ferrous sulfate is present in the slow-release material, the ferrous sulfate will quickly enter the soil near the root system in a short period of time, undergo a hydrolysis reaction in the water body, and make the soil around the root system acidic. And activate the reduced heavy metals in the soil, making them change from the passivated reduced state to the free ion state. In a short period of time, a large number of heavy metal ions gather around the root system. Other heavy metal ions in the soil will induce the rice root system to express transport proteins such as cadmium and arsenic ions, resulting in a decrease in the antagonistic effect after the subsequent release of iron ions, and losing the advantage of the coated slow-release material. However, if ferrous sulfate is impregnated in the front and calcium hydroxide is impregnated in the back, the ferrous sulfate is basically consumed. The vast majority of the slow-release fertilizer is ferric hydroxide, without ferrous sulfate. Before the ferric hydroxide is released, there is no iron ion to antagonize. Other heavy metal ions in the soil will induce the rice root system to express transport proteins such as cadmium and arsenic ions, creating obstacles for the subsequent iron ion antagonism. Therefore, in the present invention, calcium hydroxide is impregnated in the back. The calcium sulfate is impregnated in the front and the ferrous sulfate is impregnated in the back, so that most of the ferrous sulfate is converted into ferric hydroxide precipitation load, but a small amount of ferrous sulfate will remain in the pores of the porous material. This part of the ferrous sulfate can quickly enter the soil when the coating fails, and can quickly provide iron ions to antagonize the absorption of cadmium and arsenic ions in the early stage of rice growth. On the one hand, the content of ferrous sulfate is relatively small at this time, which is not enough to cause strong acidity of the water body, and the alkaline coating of the present invention will also consume the acidic environment in the soil before it fails in the field, neutralizing the acidity enhancement brought by ferrous sulfate. On the other hand, the alkaline coating, alkaline adhesive and alkaline precipitated ferric hydroxide and ferrous hydroxide of the present invention, due to their alkalinity, will reduce the acidity of the soil in the field, thereby passivating the reduced heavy metals in the soil.Reduce the mobility of cadmium and arsenic. In addition, since the precipitation is generated in the porous material and is covered by the calcium sulfate particles, a part of the ferrous hydroxide precipitation can be retained while the ferrous hydroxide precipitation is generated. 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, and reducing the conversion of heavy metal reduced state to oxidized ionic state. It will not activate the heavy metal ions in the soil, causing them to convert from free ionic state to passivated reduced state, passivating and fixing the heavy metals around the soil roots. In this environment, a small amount of excess ferrous sulfate in the early stage provides antagonism in the early stage of rice growth. The precipitated ferric hydroxide and ferrous hydroxide are mixed and wrapped by the by-product calcium sulfate and evenly dispersed and attached to the pores of the porous adsorbent. The precipitated ferric hydroxide and ferrous hydroxide can achieve long-term iron ion slow release, and perform iron ion antagonism throughout the entire process of rice growth. The alkaline coating, alkaline adhesive and alkaline precipitated ferric hydroxide and ferrous hydroxide can antagonize the hydrolysis acidity of slightly excess ferrous sulfate and provide an alkaline soil environment. The synergistic effect of the above conditions achieves better heavy metal antagonism of the coated slow-release material. At the same time, by precisely spreading 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) in the field, the slow-release material is concentrated in the rice rhizosphere at a high concentration 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. It has excellent application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a schematic structural diagram of a precipitation-loaded alkaline coated slow-release carbon-based iron fertilizer 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 rice seedling cultivation in a rice seedling field according to an embodiment of the present invention;

[0030] Figure 3 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

[0031] 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:

[0032] 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.

[0033] Example 1:

[0034] In this embodiment, the preparation method of the biological crustacean adsorbent is:

[0035] The biocrusts were treated at 300°C for 2 hours in the absence of oxygen.

[0036] Modifying the treated biological crust to obtain the modified biological crust adsorbent comprises the following steps:

[0037] 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;

[0038] 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;

[0039] 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.

[0040] The preparation method of a precipitation-loaded alkaline coated slow-release carbon-based iron fertilizer of this embodiment is as follows, comprising the following steps:

[0041] 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;

[0042] 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 biological crustacean particles with a slightly excess of ferrous sulfate; the concentration of the FeSO4 solution is 5.5%; the immersion time is more than 4 hours; and the volume ratio of the FeSO4 solution to the biological crustacean adsorbent particles dried in step S1 is 1.5:1;

[0043] Step S3: using an adhesive, the adhesive including 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, 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 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 to obtain a precipitated slow-release carbon-based iron fertilizer;

[0044] Step S4: at room temperature, using an alkaline material as a coating, the alkaline material is quicklime, and the precipitated loaded slow-release carbon-based iron fertilizer in step S3 is used as the fertilizer core, and the mass ratio of the coating material to the precipitated loaded slow-release carbon-based iron fertilizer is 1:1; adding the precipitated loaded slow-release carbon-based iron fertilizer and the coating material to a granulator, spraying a saturated sodium carbonate aqueous solution in small amounts and multiple times, the amount of saturated sodium carbonate solution added is 15% of the total mass of the precipitated loaded slow-release carbon-based iron fertilizer and the alkaline material coating; coating the precipitated loaded slow-release carbon-based iron fertilizer, drying at a low temperature of 40°C until the outer surface is dry, sieving after drying, and the particle size is 4mm; the prepared coating material is fully hardened at room temperature for not less than 48h; the precipitated loaded alkaline coated slow-release carbon-based iron fertilizer 1 is obtained, such as Figure 1 shown.

[0045] Example 2:

[0046] In this embodiment, the preparation method of the biological crustacean adsorbent is:

[0047] The bio-crusts were treated at 600°C for 3 hours in the absence of oxygen.

[0048] Modifying the treated biological crust to obtain the modified biological crust adsorbent comprises the following steps:

[0049] 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;

[0050] 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;

[0051] 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.

[0052] The preparation method of a precipitation-loaded alkaline coated slow-release carbon-based iron fertilizer of this embodiment is as follows, comprising the following steps:

[0053] 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 65°C; the concentration of the Ca(OH)2 solution is 6.67%; the impregnation 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;

[0054] 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 65°C to obtain iron-based biological crustacean particles with a slightly excess of ferrous sulfate; the concentration of the FeSO4 solution is 10%; 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 2:1;

[0055] Step S3: using an adhesive, the adhesive including 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, 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 S3 according to the mass ratio, drying at a low temperature of 55° C., and sieving after drying to obtain a particle size of 3 mm to obtain a precipitated slow-release carbon-based iron fertilizer;

[0056] Step S4: At room temperature, an alkaline material is used as a coating, wherein the alkaline material is slaked lime, and the precipitated loaded slow-release carbon-based iron fertilizer in step S3 is used as the fertilizer core, and the mass ratio of the coating material to the precipitated loaded slow-release carbon-based iron fertilizer is 1:3; the precipitated loaded slow-release carbon-based iron fertilizer and the coating material are added to a granulator, and a saturated sodium bicarbonate aqueous solution is sprayed in small amounts and multiple times, and the amount of the saturated sodium bicarbonate aqueous solution added is 20% of the total mass of the precipitated loaded slow-release carbon-based iron fertilizer and the alkaline material coating; the precipitated loaded slow-release carbon-based iron fertilizer is coated, dried at a low temperature of 45°C until the outer surface is dry, and sieved after drying to a particle size of 5 mm; the prepared coating material is fully hardened at room temperature for not less than 48 hours; the precipitated loaded alkaline coated slow-release carbon-based iron fertilizer 2 is obtained.

[0057] Comparative Example 1:

[0058] Based on Example 1:

[0059] In this comparative example, the preparation method of the biological crustacean adsorbent is the same as that in Example 1.

[0060] The preparation method of a common loaded slow-release carbon-based iron fertilizer in this comparative example is as follows, comprising the following steps:

[0061] 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 5.5%; the immersion time is more than 4 hours; and the volume ratio of the FeSO4 solution to the biological crustacean adsorbent particles is 1.5:1;

[0062] Step S2: using an adhesive, the adhesive including gypsum, quicklime, and slaked lime; the mass ratio of gypsum to iron-based loaded biological crustacean particles is 1:3, the mass ratio of quicklime to iron-based loaded biological crustacean particles is 1:4, and the mass ratio of slaked lime to iron-based 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 iron-based 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 particle size of 2 mm to obtain a common loaded slow-release carbon-based iron fertilizer;

[0063] Step S4: At room temperature, an alkaline material is used as a coating, wherein the alkaline material is quicklime, and the ordinary loaded slow-release carbon-based iron fertilizer in step S3 is used as the fertilizer core, and the mass ratio of the coating material to the ordinary loaded slow-release carbon-based iron fertilizer is 1:1; the ordinary loaded slow-release carbon-based iron fertilizer and the coating material are added to a granulator, and a saturated sodium carbonate aqueous solution is sprayed in small amounts and multiple times, and the amount of saturated sodium carbonate solution added is 15% of the total mass of the ordinary loaded slow-release carbon-based iron fertilizer and the alkaline material coating; the ordinary loaded slow-release carbon-based iron fertilizer is coated, dried at a low temperature of 40°C until the outer surface is dry, and sieved after drying, with a particle size of 4mm; the prepared coating material is fully hardened at room temperature for not less than 48h; the ordinary loaded alkaline coated slow-release carbon-based iron fertilizer 3 is obtained.

[0064] Comparative Example 2:

[0065] In this comparative example, the preparation method of the biological crustacean adsorbent is the same as that in Example 1.

[0066] The preparation method of a common loaded slow-release carbon-based iron fertilizer in this comparative example is as follows, comprising the following steps:

[0067] 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;

[0068] Step S2: using an adhesive, the adhesive including gypsum, quicklime, and slaked lime; the mass ratio of gypsum to the biological crustacean adsorbent particles loaded with ferric hydroxide powder is 1:3, the mass ratio of quicklime to the biological crustacean adsorbent particles loaded with ferric hydroxide powder is 1:4, and the mass ratio of slaked lime to the biological crustacean adsorbent particles loaded with ferric 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 ferric hydroxide powder in step S1 according to the mass ratio, low-temperature drying at 50°C, and sieving after drying to obtain a particle size of 2 mm to obtain a common loaded slow-release carbon-based iron fertilizer;

[0069] Step S4: At room temperature, an alkaline material is used as a coating, wherein the alkaline material is quicklime, and the ordinary loaded slow-release carbon-based iron fertilizer in step S3 is used as the fertilizer core, and the mass ratio of the coating material to the ordinary loaded slow-release carbon-based iron fertilizer is 1:1; the ordinary loaded slow-release carbon-based iron fertilizer and the coating material are added to a granulator, and a saturated sodium carbonate aqueous solution is sprayed in small amounts and multiple times, and the amount of saturated sodium carbonate solution added is 15% of the total mass of the ordinary loaded slow-release carbon-based iron fertilizer and the alkaline material coating; the ordinary loaded slow-release carbon-based iron fertilizer is coated, dried at a low temperature of 40°C until the outer surface is dry, and sieved after drying, with a particle size of 4mm; the prepared coating material is fully hardened at room temperature for not less than 48h; and ordinary loaded alkaline coated slow-release carbon-based iron fertilizer 4 is obtained.

[0070] Comparative Example 3:

[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 precipitated loaded slow-release carbon-based iron fertilizer of this comparative example is as follows, comprising the following steps:

[0073] 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;

[0074] 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;

[0075] Step S3: using an adhesive, the adhesive including gypsum, quicklime, and slaked lime; the mass ratio of gypsum to iron-based loaded biological crustacean particles is 1:3, the mass ratio of quicklime to iron-based loaded biological crustacean particles is 1:4, and the mass ratio of slaked lime to iron-based loaded biological crustacean particles 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 loaded biological crustacean particles 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 loaded slow-release carbon-based iron fertilizer;

[0076] Step S4: At room temperature, an alkaline material is used as a coating, wherein the alkaline material is quicklime, and the precipitated loaded slow-release carbon-based iron fertilizer in step S3 is used as the fertilizer core, and the mass ratio of the coating material to the precipitated loaded slow-release carbon-based iron fertilizer is 1:1; the precipitated loaded slow-release carbon-based iron fertilizer and the coating material are added to a granulator, and a saturated sodium carbonate aqueous solution is sprayed in small amounts and multiple times, and the amount of saturated sodium carbonate solution added is 15% of the total mass of the precipitated loaded slow-release carbon-based iron fertilizer and the alkaline material coating; the precipitated loaded slow-release carbon-based iron fertilizer is coated, dried at a low temperature of 40°C until the outer surface is dry, and sieved after drying, with a particle size of 4 mm; the prepared coating material is fully hardened at room temperature for not less than 48 hours; the precipitated loaded alkaline coated slow-release carbon-based iron fertilizer 5 is obtained.

[0077] Comparative Example 4:

[0078] In this comparative example, the preparation method of the biological crustacean adsorbent is the same as that in Example 1.

[0079] The preparation method of a precipitated loaded slow-release carbon-based iron fertilizer of this comparative example is as follows, comprising the following steps:

[0080] 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;

[0081] Step S2: The biological crustacean adsorbent particles dried in step S1 are immersed in a FeSO4 solution, the immersed biological crustacean adsorbent particles are removed and filtered, and then immersed in clean water for more than 6 hours, removed and filtered, and then low-temperature dried 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;

[0082] Step S3: using an adhesive, the adhesive including gypsum, quicklime, and slaked lime; the mass ratio of gypsum to iron-based loaded biological crustacean particles is 1:3, the mass ratio of quicklime to iron-based loaded biological crustacean particles is 1:4, and the mass ratio of slaked lime to iron-based loaded biological crustacean particles 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 loaded biological crustacean particles 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 loaded slow-release carbon-based iron fertilizer;

[0083] Step S4: At room temperature, an alkaline material is used as a coating, wherein the alkaline material is quicklime, and the precipitated loaded slow-release carbon-based iron fertilizer in step S3 is used as the fertilizer core, and the mass ratio of the coating material to the precipitated loaded slow-release carbon-based iron fertilizer is 1:1; the precipitated loaded slow-release carbon-based iron fertilizer and the coating material are added to a granulator, and a saturated sodium carbonate aqueous solution is sprayed in small amounts and multiple times, and the amount of saturated sodium carbonate solution added is 15% of the total mass of the precipitated loaded slow-release carbon-based iron fertilizer and the alkaline material coating; the precipitated loaded slow-release carbon-based iron fertilizer is coated, dried at a low temperature of 40°C until the outer surface is dry, and sieved after drying, with a particle size of 4mm; the prepared coating material is fully hardened at room temperature for not less than 48h; the precipitated loaded alkaline coated slow-release carbon-based iron fertilizer 6 is obtained.

[0084] Comparative Example 5:

[0085] In this comparative example, the preparation method of the biological crustacean adsorbent is the same as that in Example 1.

[0086] The preparation method of a precipitated loaded slow-release carbon-based iron fertilizer of this comparative example is as follows, comprising the following steps:

[0087] 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;

[0088] 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;

[0089] 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.

[0090] 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;

[0091] Step S5: At room temperature, an alkaline material is used as a coating, wherein the alkaline material is quicklime, and the precipitated loaded slow-release carbon-based iron fertilizer in step S3 is used as the fertilizer core, and the mass ratio of the coating material to the precipitated loaded slow-release carbon-based iron fertilizer is 1:1; the precipitated loaded slow-release carbon-based iron fertilizer and the coating material are added to a granulator, and a saturated sodium carbonate aqueous solution is sprayed in small amounts and multiple times, and the amount of saturated sodium carbonate solution added is 15% of the total mass of the precipitated loaded slow-release carbon-based iron fertilizer and the alkaline material coating; the precipitated loaded slow-release carbon-based iron fertilizer is coated, dried at a low temperature of 40°C until the outer surface is dry, and sieved after drying, with a particle size of 4 mm; the prepared coating material is fully hardened at room temperature for not less than 48 hours; the precipitated loaded alkaline coated slow-release carbon-based iron fertilizer 7 is obtained.

[0092] The slow-release carbon-based iron fertilizers in Examples 1-2 and Comparative Examples 1-5 are evaluated below:

[0093] 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 24 plots, each with an area of 30 m 2 , every 3 plots were a treatment area, with a total of 8 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 2-8 were the slow-release carbon-based iron fertilizer passivation agents in Examples 1-2 and Comparative Examples 1-5, respectively; the same rice variety was planted in all of them, namely Taiyou 398.

[0094] Rice seedlings are raised in the field or in mechanized rice seedling trays. During the preparation of rice seedling trays, a total of 7 slow-release carbon-based iron fertilizer passivators (3 plots for each slow-release carbon-based iron fertilizer passivator) according to Examples 1-2 and Comparative Examples 1-5 are evenly applied to the rice seedling trays at a rate of 30 kg / mu (the ratio of rice seedlings to transplanted fields is 1:10, and the actual field rate is 3 kg / mu) and covered with rice seedling soil. The application effect is as follows: Figure 2 and Figure 3A 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.

[0095] 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 seedling cultivation conditions) or mechanical transplanting (under mechanized seedling cultivation conditions), carrying the root soil or seedling medium with them. Apply 8 kg / mu of urea during the tillering stage. Other field water and fertilizer management methods and pest and disease control measures remain the same as traditional methods. After rice matures, harvest and measure yield in each plot, and measure cadmium and arsenic content in the rice.

[0096] The cadmium and arsenic content of 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 sample was covered and then digested overnight. The sample was digested in a graphite digester for 2 hours and the volume was adjusted to 25 mL. The cadmium and arsenic concentrations in the digestate were analyzed using an inductively coupled plasma mass spectrometer. The test results are shown in Table 1.

[0097] Table 1 Differences in rice yield and cadmium content in brown rice among treatments

[0098] 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 1 544±17 0.062±0.004 0.115±0.006 3 Example 2 537±28 0.066±0.005 0.110±0.008 4 Comparative Example 1 551±20 0.406±0.017 0.465±0.034 5 Comparative Example 2 528±19 0.332±0.031 0.382±0.029 6 Comparative Example 3 545±25 0.084±0.018 0.134±0.013 7 Comparative Example 4 539±14 0.088±0.024 0.132±0.009 8 Comparative Example 5 544±22 0.231±0.013 0.306±0.044

[0099] Note 1: Except for the different treatment methods, the other conventional cultivation methods of each group in the table are the same.

[0100] 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.

[0101] In summary, the present invention provides a precipitation-loaded alkaline coated slow-release carbon-based iron fertilizer, a preparation method and a precise application method thereof. The preparation method is specifically as follows: a biological crustacean heavy metal adsorbent is impregnated with a calcium hydroxide solution, dried at low temperature, and then impregnated with a ferrous sulfate solution again. The particles obtained by drying are granulated and then alkaline coated. This coated slow-release iron fertilizer is loaded by precipitation, and the precipitated ferric hydroxide, ferrous hydroxide and slightly excess ferric sulfate are uniformly dispersed and attached to the pores of the porous adsorbent. The byproduct calcium sulfate in the porous adsorbent coats the precipitated ferric hydroxide and ferrous hydroxide, which can achieve long-term slow release of iron ions and reduce soil oxygen content. The slightly excess ferric sulfate can quickly provide iron ions in the early stage of rice growth to antagonize the absorption of cadmium and arsenic ions. The coated iron fertilizer is used in a precise amount during the rice seedling raising period, and iron ion antagonism is carried out throughout the rice growth process. The precipitation-type adsorption loading method and the coating material greatly increase the release period of iron ions. Compared with traditional slow-release fertilizers, the iron fertilizer of the present invention has an excellent cadmium and arsenic antagonistic effect on rice, and a smaller amount can greatly reduce the cadmium content of 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 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 a large amount of ferrous sulfate is present in the slow-release material, the ferrous sulfate will quickly enter the soil near the root system in a short period of time, undergo a hydrolysis reaction in the water body, and make 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. In a short period of time, a large number of heavy metal ions gather around the root system. Other heavy metal ions in the soil will induce the rice root system to express transport proteins such as cadmium and arsenic ions, resulting in a decrease in the antagonistic effect after the subsequent release of iron ions, and losing the advantage of the coated slow-release material. However, if ferrous sulfate is impregnated in the front and calcium hydroxide is impregnated in the back, the ferrous sulfate is basically consumed. The vast majority of the slow-release fertilizer is ferric hydroxide, without ferrous sulfate. Before the ferric hydroxide is released, there is no iron ion to antagonize. Other heavy metal ions in the soil will induce the rice root system to express transport proteins such as cadmium and arsenic ions, creating obstacles for the subsequent iron ion antagonism. Therefore, in the present invention, hydrogen Calcium oxide is impregnated in the front and ferrous sulfate is impregnated once in the back, so that most of the ferrous sulfate is converted into ferric hydroxide precipitation load, but a small amount of ferrous sulfate will remain in the pores of the porous material. This part of ferrous sulfate can quickly enter the soil when the coating fails, and can quickly provide iron ions to antagonize the absorption of cadmium and arsenic ions in the early stage of rice growth. On the one hand, the content of ferrous sulfate is relatively small at this time, which is not enough to cause strong acidity of the water body, and the alkaline coating of the present invention will also consume the acidic environment in the soil before it fails in the field, neutralizing the acidity enhancement brought by ferrous sulfate. On the other hand, the alkaline coating, alkaline adhesive and alkaline precipitated ferric hydroxide and ferrous hydroxide of the present invention, due to their alkalinity, will reduce the acidity of the soil in the field, thereby passivating the reduced heavy metals in the soil.Reduce the mobility of cadmium and arsenic. In addition, since the precipitation is generated in the porous material and is covered by the calcium sulfate particles, a part of the ferrous hydroxide precipitation can be retained while the ferrous hydroxide precipitation is generated. 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, and reducing the conversion of heavy metal reduced state to oxidized ionic state. It will not activate the heavy metal ions in the soil, causing them to convert from free ionic state to passivated reduced state, passivating and fixing the heavy metals around the soil roots. In this environment, a small amount of excess ferrous sulfate in the early stage provides antagonism in the early stage of rice growth. The precipitated ferric hydroxide and ferrous hydroxide are mixed and wrapped by the by-product calcium sulfate and evenly dispersed and attached to the pores of the porous adsorbent. The precipitated ferric hydroxide and ferrous hydroxide can achieve long-term iron ion slow release, and perform iron ion antagonism throughout the entire process of rice growth. The alkaline coating, alkaline adhesive and alkaline precipitated ferric hydroxide and ferrous hydroxide can antagonize the hydrolysis acidity of slightly excess ferrous sulfate and provide an alkaline soil environment. The synergistic effect of the above conditions achieves better heavy metal antagonism of the coated slow-release material. At the same time, by precisely spreading 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) in the field, the slow-release material is concentrated in the rice rhizosphere at a high concentration 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. It has excellent application prospects.

[0102] 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 alkaline coated slow-release carbon-based iron fertilizer, characterized in that: The preparation method comprises the following steps: Step S1: crushing the bio-crust adsorbent into particles with a diameter not greater than 1 mm, impregnating with Ca(OH)2 solution, filtering and drying at low temperature; Step S2: The biocrust adsorbent particles dried in step S1 are immersed in a FeSO4 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 biocrust particles with a slightly excess of ferrous sulfate; Step S3: using an adhesive, granulating the iron-based loaded biological shell particles with a slightly excess of ferrous sulfate in step S2 according to a mass ratio, drying at low temperature, and sieving after drying to obtain a precipitated loaded slow-release carbon-based iron fertilizer; Step S4: at room temperature, using an alkaline material as a coating, wherein the alkaline material is one or both of quicklime and slaked lime, and using the precipitated loaded slow-release carbon-based iron fertilizer in step S3 as the fertilizer core, adding the precipitated loaded slow-release carbon-based iron fertilizer and the coating material to a granulator according to a mass ratio, spraying a saturated sodium carbonate or saturated sodium bicarbonate aqueous solution in small amounts and multiple times, wherein the amount of saturated sodium carbonate or saturated sodium bicarbonate solution added is 15-20% of the total mass of the precipitated loaded slow-release carbon-based iron fertilizer and the alkaline material coating; coating the precipitated loaded slow-release carbon-based iron fertilizer, drying at low temperature until the outer surface is dry, and sieving after drying to a particle size of 4-5 mm; the prepared coating material is fully hardened at room temperature; and the precipitated loaded alkaline coated slow-release carbon-based iron fertilizer is obtained; 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; the ratio of the concentration of the FeSO4 solution to the concentration of the Ca(OH)2 solution is 1.1 to 1.5:1; The preparation method of the biological crustacean adsorbent is: Under the condition of isolating oxygen, 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 of the treated biocrust 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% to 60% NaOH solution; the mass ratio of the treated biocrust: alkali: chloroacetic acid is 1: (2-4): (1.2-3); dialdehydeation: reacting the carboxymethyl biocrust with an oxidant to obtain a dialdehyde carboxymethyl biocrust; the oxidant The invention relates to a biocrust adsorbent comprising: periodic acid and its salts; the mass ratio of the oxidant to the carboxymethyl biocrust is (1-2):1; a Schiff base reaction is carried out in which the dialdehyde carboxymethyl biocrust reacts with an amino compound to obtain a dialdehyde carboxymethyl biocrust Schiff base, which is a biocrust 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 mass ratio of the amino compound to the dialdehyde carboxymethyl biocrust is (1-5):1; and the biocrust is one or more of shrimp shells, tortoise shells, crab shells, turtle shells, and fish scales.

2. The method for preparing a precipitation-loaded alkaline coated slow-release carbon-based iron fertilizer as claimed in claim 1, characterized in that: The mass ratio of the coating material to the precipitated loaded slow-release carbon-based iron fertilizer in step S4 is 1:1-1:3; the drying temperature after coating is 40-45° C.; and the sufficient hardening time at room temperature is not less than 48 hours.

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

1.

4. The method for preparing a precipitation-loaded alkaline 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.

5. The method for preparing a precipitation-loaded alkaline 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 granulated, 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 biocrust particles with a slightly excess of ferrous sulfate is 1:3-1:5, and the preparation method of the precipitated loaded slow-release carbon-based iron fertilizer in step S3 is filtered through a mesh screen, and the particle size is 2-3 mm.

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

5.

7. A precipitation-loaded alkaline 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 6.

8. The method for precise application of a precipitation-loaded alkaline coated slow-release carbon-based iron fertilizer according to claim 7, characterized in that: The application of the precipitated alkaline coated slow-release carbon-based iron fertilizer in reducing cadmium ion absorption by rice is as follows: a small amount of the precipitated alkaline coated slow-release carbon-based iron fertilizer is applied to the rice seedling raising substrate during the rice seedling raising period; during the rice seedling raising and transplanting process, the rice seedling raising substrate wrapped in the rice root system or the root soil carried by the rice root system is transferred to the production field together, 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 1:10-1:15.

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