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

Abstract

The invention discloses a precipitation-loaded slow-release carbon-based iron fertilizer and a preparation method thereof. The preparation method specifically comprises the following steps: firstly, a biological crustacean heavy metal adsorbent is immersed in a calcium hydroxide solution, dried, and then immersed in a ferrous sulfate solution twice, and finally dried and granulated. The slow-release iron fertilizer is loaded by precipitation, and a precipitated ferric hydroxide, ferrous hydroxide mixture and excess ferric sulfate are uniformly dispersed and attached to the inside of pores of a porous adsorbent. Excess ferric sulfate can quickly provide iron ions to antagonize cadmium and arsenic ion absorption in the early growth stage of rice. Calcium sulfate encapsulates the precipitated ferric hydroxide and ferrous hydroxide in the porous adsorbent, which can achieve long-term slow-release of iron ions and reduce soil oxygen content. Iron ion antagonism is performed throughout the entire rice growth process. The precipitation-type adsorption loading method greatly increases the release cycle of the iron ions. The iron fertilizer of the invention has an excellent cadmium and arsenic antagonistic effect on rice and has excellent application prospects.

Description

Technical Field

[0001] The present invention relates to the technical field of safe rice production in heavy metal-contaminated paddy fields, and in particular to a precipitation-loaded 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 has faced increasingly serious soil environmental safety issues, with heavy metal pollution receiving particular attention. Currently, to fulfill the primary responsibility for food security, extensive and sustained research is being conducted across the country on the safe use of contaminated farmland, particularly that contaminated by cadmium and arsenic, with some success.

[0003] In reality, heavy metal contaminants that enter the soil cannot be easily and quickly removed from the soil. Currently, the main method used for remediating contaminated soil is chemical remediation via passivation / stabilization. This method does not reduce the total amount of heavy metals in the soil. Instead, it uses chemical remediation agents added to the soil to undergo chemical reactions such as oxidation, reduction, and ion exchange with the contaminants, reducing their mobility and bioavailability. This approach, in turn, curbs their impact and ecological risks, reduces the uptake of heavy metals by crops like rice, and ensures the safe production of agricultural products. Carbon-based materials, due to their unique pore structure, high surface negative charge density, and numerous oxygen-containing functional groups, can adsorb and fix heavy metal ions, thereby reducing their available concentration in the soil and mitigating their toxicity to plants. Consequently, they have garnered considerable attention. For example, treatment with pig bone biochar reduced the effective Cd leaching rate in soil by 38%; treatment with oak biochar reduced the Cd concentration in soil pore water by 66.0%; and application of rice husk biochar reduced the Cd content in rapeseed aboveground by 68.40% and in underground by 60.62%.

[0004] However, biochars prepared from different raw materials exhibit varying effects on soil Cd fixation, influenced by factors such as the raw material structure and composition. Existing carbon-based passivation materials also suffer from technical drawbacks such as high cost, insufficient long-term effectiveness, and high passivation agent dosages, typically requiring application rates of 200-300 kg / mu. Therefore, it is necessary to design a carbon-based passivation material that can reduce the bioavailability of cadmium and arsenic in soil. Such a material should possess long-term antagonistic effects and exhibit a significant 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 slow-release carbon-based iron fertilizer and a preparation method thereof. The preparation method is specifically as follows: first, a biological crustacean heavy metal adsorbent is immersed in a calcium hydroxide solution, dried, immersed in a ferrous sulfate solution twice, and finally dried and granulated. The slow-release iron fertilizer is loaded by precipitation, and the precipitated ferric hydroxide, ferrous hydroxide mixture and excess ferric sulfate are uniformly dispersed and attached to the pores of the porous adsorbent. Excess ferric sulfate can quickly provide iron ions to antagonize the absorption of cadmium and arsenic ions in the early stage of rice growth. The calcium sulfate-coated precipitated ferric hydroxide and ferrous hydroxide can achieve long-term slow-release of iron ions and reduce soil oxygen content. After application in the field, iron ion antagonism is carried out throughout the entire process of rice growth. The precipitation-type adsorption loading method greatly increases the release period 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 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 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 biological crustacean 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 loaded biological crustacean particles;

[0010] Step S3: The iron-based biocrust particles dried in step S2 are immersed in a FeSO4 solution again, removed, 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 an excess of ferrous sulfate;

[0011] Step S4: using an adhesive, granulating the iron-based loaded biological crustacean particles with excess ferrous sulfate in step S3 according to a mass ratio, drying at low temperature, and sieving after drying to obtain a precipitation-loaded slow-release carbon-based iron fertilizer.

[0012] Furthermore, the concentration of the Ca(OH)2 solution in step S1 is 5% to 10%; and the immersion time is more than 4 hours.

[0013] Furthermore, in step S2, the concentration of the FeSO4 solution is 5% to 10%; the immersion time is more than 4 hours; in step S3, the concentration of the FeSO4 solution is 5% to 10%; the immersion time is more than 1 hour.

[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; 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; the ratio of the volume of the FeSO4 solution in step S3 to the biological crust adsorbent particles dried in step S2 is 1~1.5:1.

[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; the mass ratio of the adhesive to the iron-based biocrust particles with excess ferrous sulfate is 1:3~1:5, and water is added for bonding and then granulation, and the amount of water added is 30-40% of the total mass of the adhesive; the low-temperature drying temperature in step S4 is 50~55°C, and the precipitated loaded slow-release carbon-based iron fertilizer in step S4 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 biocrust particles with excess ferrous sulfate is 1:3, the mass ratio of the quicklime to the iron-based biocrust particles with excess ferrous sulfate is 1:3, and the mass ratio of the slaked lime to the iron-based biocrust particles with excess 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 slow-release carbon-based iron fertilizer is prepared by any of the above preparation methods.

[0025] The invention relates to an application of the precipitation-loaded slow-release carbon-based iron fertilizer in reducing cadmium ion absorption by rice.

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

[0027] The invention discloses a precipitation-loaded slow-release carbon-based iron fertilizer and a preparation method thereof. The invention uniformly loads ferric hydroxide and ferrous hydroxide into a porous material by precipitation. The specific method is as follows: first, a biological crustacean heavy metal adsorbent is immersed in a calcium hydroxide solution, filtered and dried at low temperature, and then immersed again in a ferrous sulfate solution with a slightly higher concentration, filtered and dried to obtain particles, and then immersed again in a ferrous sulfate solution with a slightly higher concentration, filtered and dried to obtain particles, and granulated to obtain the precipitation-loaded slow-release carbon-based iron fertilizer. The slow-release iron fertilizer is loaded by precipitation, and the precipitated ferric hydroxide and ferrous hydroxide are simultaneously generated with the precipitation of ferric hydroxide and ferrous hydroxide, and the calcium sulfate particles mixed with the precipitate are uniformly dispersed and attached to the pores inside the porous adsorbent to synergistically act, so that the excess ferric sulfate can quickly provide iron ions for rice growth in the early stage. Antagonize the absorption of cadmium and arsenic ions and reduce the expression of cadmium and arsenic ion transport proteins in rice roots; the biological crustacean adsorbent, precipitated ferric hydroxide and ferrous hydroxide, and calcium sulfate particles generated simultaneously with the precipitation and mixed in the precipitate work together to achieve long-term iron ion slow release. After application in the field, iron ion antagonism is carried out throughout the growth process of rice to reduce the absorption of cadmium and arsenic ions by rice. The precipitation-type loading method and the mixed coating of the reaction product calcium sulfate greatly improve the iron ion release pattern and speed through the adsorption and precipitation effect of porous materials, and greatly increase the iron ion release cycle. 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 the porous material and has the covering and coating effect of calcium sulfate particles, a part 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 with itself to generate ferric hydroxide precipitate, and also consume oxygen in the soil, thereby reducing the oxygen content in the soil, reducing the oxygen content in the rhizosphere of rice, and reducing the ionic conversion of heavy metals from a reduced state to an oxidized state. The multiple effects work synergistically with each other. Compared with traditional slow-release fertilizers, the precipitation-loaded slow-release carbon-based iron fertilizer of the present invention has an excellent antagonistic effect on cadmium and arsenic in rice, can achieve a significant reduction in the cadmium content in rice with a smaller dosage, and has excellent application prospects. DETAILED DESCRIPTION

[0028] The present invention is further described below, and the protection scope of the present invention is not limited to the following:

[0029] 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.

[0030] Example 1:

[0031] In this embodiment, the preparation method of the biological crustacean adsorbent is:

[0032] The biocrusts were treated at 300°C for 2 hours in the absence of oxygen.

[0033] Modifying the treated biological crust to obtain the modified biological crust adsorbent comprises the following steps:

[0034] 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;

[0035] 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;

[0036] 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.

[0037] The preparation method of a precipitation-loaded slow-release carbon-based iron fertilizer of this embodiment is as follows, comprising the following steps:

[0038] 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;

[0039] 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;

[0040] 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.

[0041] Step S4: using an adhesive, the adhesive including 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, 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 precipitated loaded slow-release carbon-based iron fertilizer 1.

[0042] Example 2:

[0043] In this embodiment, the preparation method of the biological crustacean adsorbent is:

[0044] The bio-crusts were treated at 600°C for 3 hours in the absence of oxygen.

[0045] Modifying the treated biological crust to obtain the modified biological crust adsorbent comprises the following steps:

[0046] 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;

[0047] 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;

[0048] 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.

[0049] The preparation method of a precipitation-loaded slow-release carbon-based iron fertilizer of this embodiment is as follows, comprising the following steps:

[0050] 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;

[0051] 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 loaded biological crustacean particles; 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;

[0052] 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 65°C to obtain iron-based loaded biological crust particles with excess ferrous sulfate; the concentration of the FeSO4 solution is 10%; 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 1.5:1.

[0053] Step S4: using an adhesive, the adhesive includes 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, the amount of water added is 40% 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 55°C, and sieving after drying to obtain a precipitated loaded slow-release carbon-based iron fertilizer 2.

[0054] Example 3:

[0055] In this embodiment, the preparation method of the biological crustacean adsorbent is:

[0056] The biocrusts were treated at 500°C for 2.5 hours in the absence of oxygen.

[0057] Modifying the treated biological crust to obtain the modified biological crust adsorbent comprises the following steps:

[0058] Carboxymethylation: reacting the treated biocrust with chloroacetic acid in an alkaline solution to obtain a carboxymethylated biocrust; the alkaline solution is a 30% NaOH solution; the mass ratio of the treated biocrust: alkali: chloroacetic acid is 1:3:2;

[0059] 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 1.5:1;

[0060] 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 m-phenylenediamine; the mass ratio of the water-soluble amino compound to the dialdehyde carboxymethyl biological crust is 3:1; the biological crust is fish scale.

[0061] The preparation method of a precipitation-loaded slow-release carbon-based iron fertilizer of this embodiment is as follows, comprising the following steps:

[0062] 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 60°C; the concentration of the Ca(OH)2 solution is 6%; the impregnation time is more than 4 hours; and the volume ratio of the Ca(OH)2 solution to the biocrust adsorbent particles is 1.3:1;

[0063] 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 60°C to obtain iron-based loaded biological crustacean particles; the concentration of the FeSO4 solution is 9%; 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 1.8:1;

[0064] 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 60°C to obtain iron-based loaded biological crust particles with excess ferrous sulfate; the concentration of the FeSO4 solution is 9%; 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 1.3:1.

[0065] Step S4: using an adhesive, the adhesive includes one or more of raw gypsum, quicklime, and slaked lime; the mass ratio of raw gypsum 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, 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 low temperature, the temperature is 55°C, and sieving after drying to obtain precipitation-loaded slow-release carbon-based iron fertilizer 3.

[0066] Comparative Example 1:

[0067] Based on Example 1:

[0068] In this comparative example, the preparation method of the biological crustacean adsorbent is the same as that in Example 1.

[0069] The preparation method of a common loaded slow-release carbon-based iron fertilizer in this comparative example is as follows, comprising the following steps:

[0070] 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;

[0071] Step S2: The iron-based loaded biological crustacean particles dried in step S1 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 crustacean particles; 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 S1 is 1:1.

[0072] Step S3: using an adhesive, the adhesive includes gypsum, quicklime, and slaked lime; the mass ratio of gypsum to iron-based loaded biological crust particles is 1:3, the mass ratio of quicklime to iron-based loaded biological crust particles is 1:4, and the mass ratio of slaked lime to iron-based loaded biological crust particles is 1:5; adding water for bonding and then granulating, the amount of water added is 30% of the total mass of the adhesive; granulating the iron-based loaded biological crust particles in step S2 according to the mass ratio, drying at a low temperature of 50°C, and sieving after drying to obtain ordinary loaded slow-release carbon-based iron fertilizer 4.

[0073] Comparative Example 2:

[0074] In this comparative example, the preparation method of the biological crustacean adsorbent is the same as that in Example 1.

[0075] The preparation method of a common loaded slow-release carbon-based iron fertilizer in this comparative example is as follows, comprising the following steps:

[0076] 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;

[0077] Step S2: using an adhesive, the adhesive includes gypsum, quicklime, and slaked lime; the mass ratio of quicklime to the biological crustacean adsorbent particles loaded with iron hydroxide powder is 1:3, the mass ratio of quicklime to the biological crustacean adsorbent particles loaded with iron hydroxide powder is 1:4, and the mass ratio of slaked lime to the biological crustacean adsorbent particles loaded with iron hydroxide powder is 1:5; adding water for bonding and then granulating, the amount of water added is 30% of the total mass of the adhesive; granulating the biological crustacean adsorbent particles loaded with iron hydroxide powder in step S1 according to the mass ratio, drying at a low temperature of 50°C, and sieving after drying to obtain ordinary loaded slow-release carbon-based iron fertilizer 5.

[0078] Comparative Example 3:

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

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

[0081] 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 5.5%; the impregnation time is more than 4 hours; and the volume ratio of the FeSO4 solution to the biocrust adsorbent particles is 1:1;

[0082] 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%; 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;

[0083] Step S3: using an adhesive, the adhesive includes gypsum, quicklime, and slaked lime; the mass ratio of gypsum to iron-based loaded biological crust particles is 1:3, the mass ratio of quicklime to iron-based loaded biological crust particles is 1:4, and the mass ratio of slaked lime to iron-based loaded biological crust particles is 1:5; adding water for bonding and then granulating, the amount of water added is 30% of the total mass of the adhesive; granulating the iron-based loaded biological crust particles in step S3 according to the mass ratio, drying at low temperature, the temperature is 50°C, and sieving after drying to obtain precipitation-loaded slow-release carbon-based iron fertilizer 6.

[0084] Comparative Example 4:

[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: using an adhesive, the adhesive includes 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 precipitation-loaded slow-release carbon-based iron fertilizer 7.

[0090] Comparative Example 5:

[0091] In this comparative example, the preparation method of the biological crustacean adsorbent is the same as that in Example 1.

[0092] The preparation method of a precipitated loaded slow-release carbon-based iron fertilizer of this comparative example is as follows, comprising the following steps:

[0093] 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;

[0094] 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;

[0095] Step S3: using an adhesive, the adhesive includes gypsum, quicklime, and slaked lime; the mass ratio of gypsum to iron-based loaded biological crust particles is 1:3, the mass ratio of quicklime to iron-based loaded biological crust particles is 1:4, and the mass ratio of slaked lime to iron-based loaded biological crust particles is 1:5; adding water for bonding and then granulating, the amount of water added is 30% of the total mass of the adhesive; granulating the iron-based loaded biological crust particles in step S3 according to the mass ratio, drying at low temperature, the temperature is 50°C, and sieving after drying to obtain precipitation-loaded slow-release carbon-based iron fertilizer 8.

[0096] The slow-release carbon-based iron fertilizers in Examples 1-3 and Comparative Examples 1-5 are evaluated below:

[0097] 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 27 plots, each with an area of ​​30 m 2 , every 3 plots were a treatment area, with a total of 9 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 2-9 were the slow-release carbon-based iron fertilizer passivation agents in Examples 1-3 and Comparative Examples 1-5, respectively; the same rice variety was planted in all of them, namely Taiyou 398.

[0098] Rice seedlings were raised in the field. Two days before transplanting the rice, 45 kg / mu of compound fertilizer (total nutrient content 45%, of which N-P2O5-K2O=15-15-15) was applied. At the same time, 50 kg / mu of iron fertilizer described in Examples 1-3 and Comparative Examples 1-5 were applied to different treatment areas respectively, and plowing was performed once to ensure that the fertilizer and iron fertilizer were fully mixed with the soil. Manual transplanting or seedling throwing can be used in the transplanting process. After the rice turned green, 8 kg / mu of urea was applied during the tillering stage. Other field water and fertilizer management methods and pest and disease control methods were consistent with traditional methods. After the rice matured, the yield of each plot was harvested and measured, and the cadmium and arsenic contents in the rice were measured.

[0099] 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.

[0100] Table 1 Differences in rice yield and cadmium and arsenic content in brown rice among treatments

[0101] 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 1 550±15 0.146±0.023 0.241±0.011 3 Example 2 541±20 0.143±0.019 0.249±0.019 4 Example 3 538±16 0.146±0.013 0.243±0.025 5 Comparative Example 1 534±22 0.417±0.031 0.458±0.047 6 Comparative Example 2 533±13 0.378±0.029 0.426±0.033 7 Comparative Example 3 529±17 0.301±0.022 0.395±0.024 8 Comparative Example 4 537±19 0.268±0.017 0.361±0.022 9 Comparative Example 5 540±11 0.347±0.028 0.437±0.026

[0102] Note 1: Except for the different treatment methods, the other conventional cultivation methods of each group in the table are the same.

[0103] 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.

[0104] In summary, the present invention discloses a precipitation-loaded slow-release carbon-based iron fertilizer and a preparation method thereof. The present invention uniformly loads ferric hydroxide and ferrous hydroxide into a porous material by precipitation. The specific method is: first, a biological crustacean heavy metal adsorbent is immersed in a calcium hydroxide solution, filtered and dried at low temperature, and then immersed again in a slightly higher concentration ferrous sulfate solution, filtered and finally dried to obtain particles, which are again immersed in a slightly higher concentration ferrous sulfate solution, filtered and finally dried to obtain particles, and granulated to obtain a precipitation-loaded slow-release carbon-based iron fertilizer. This slow-release iron fertilizer is loaded by precipitation, and its precipitated ferric hydroxide, ferrous hydroxide, and calcium sulfate particles mixed with the precipitate generated simultaneously with the precipitation of ferric hydroxide and ferrous hydroxide, and the excess ferric sulfate covered on the precipitate are uniformly dispersed and attached to the pores inside the porous adsorbent to act synergistically, so that the excess ferric sulfate can quickly provide iron in the early growth stage of rice. Ions antagonize the absorption of cadmium and arsenic ions and reduce the expression of cadmium and arsenic ion transport proteins in rice roots; biological crustacean adsorbents, precipitated ferric hydroxide and ferrous hydroxide, and calcium sulfate particles mixed with the precipitate generated at the same time as the precipitation work together to achieve long-term iron ion slow release. After application in the field, iron ion antagonism is carried out throughout the growth process of rice to reduce 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 release pattern and speed of iron ions through the adsorption and precipitation of porous materials, and greatly increase the release cycle of iron ions. Ferric hydroxide and ferrous hydroxide precipitates are alkaline precipitates, which can control the pH value of the soil and reduce the mobility of cadmium and arsenic. In addition, since the precipitate is generated in the porous material and is covered and packaged by the calcium sulfate particles, a part 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 with itself to generate ferric hydroxide precipitate, and also consume oxygen in the soil, thereby reducing the oxygen content in the soil, reducing the oxygen content in the rhizosphere of rice, and reducing the ionic conversion of heavy metals from a reduced state to an oxidized state. The multiple effects work synergistically with each other. Compared with traditional slow-release fertilizers, the precipitation-loaded slow-release carbon-based iron fertilizer of the present invention has an excellent antagonistic effect on cadmium and arsenic in rice, can achieve a significant reduction in the cadmium content in rice with a smaller dosage, and has excellent application prospects.

[0105] 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 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 of no more than 1 mm, impregnating them with a Ca(OH)2 solution, filtering them to dryness, and then drying them at low temperature; Step S2: The biological crustacean adsorbent particles dried in step S1 are immersed in a 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 loaded biological crustacean particles; Step S3: The iron-based biocrust particles dried in step S2 are immersed in a FeSO4 solution again, removed, 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 an excess of ferrous sulfate; Step S4: using an adhesive, granulating the iron-based loaded biological crustacean particles with excess ferrous sulfate in step S3 according to a mass ratio, drying at low temperature, and sieving after drying to obtain a precipitated loaded slow-release carbon-based iron fertilizer; The concentration of the Ca(OH)2 solution in step S1 is 5% to 10%; the immersion time is more than 4 hours; The concentration of the FeSO4 solution in step S2 is 5% to 10%; the immersion time is more than 4 hours; the concentration of the FeSO4 solution in step S3 is 5% to 10%; the immersion time is more than 1 hour; 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 preparation method of the biological crustacean adsorbent is: Under oxygen-free conditions, the biocrust is treated at a temperature of 300-600° C. for 2-3 hours, and the treated biocrust is modified to obtain a modified biocrust adsorbent; the modification comprises the following steps: Carboxymethylation: reacting the treated biocrust, an alkaline solution, and chloroacetic acid in a mass ratio of 1:(2-4):(1.2-3) to obtain a carboxymethyl biocrust; the alkaline solution is a 10% to 60% NaOH solution; Dialdehydeation: reacting the carboxymethylated biocrust with an oxidant at a mass ratio of 1:(1-2) to obtain a dialdehyde carboxymethylated biocrust; the oxidant is periodic acid and its salts; Schiff base reaction: the dialdehyde carboxymethyl biological crust is reacted with an amino compound in a mass ratio of 1: (1-5) to obtain a dialdehyde carboxymethyl biological crust Schiff base, which is the biological crust adsorbent; the amino compound is one or more of aniline, benzylamine, phenylethylamine, m-aminophenol, n-hexylamine, n-octylamine, aminothiazole, m-phenylenediamine, p-phenylenediamine, o-phenylenediamine, aminobenzothiazole, and m-acetylaniline; the biological crust is one or more of shrimp shells, tortoise shells, crab shells, soft-shell turtle shells, and fish scales.

2. The method for preparing a precipitation-loaded 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 to the biological crust adsorbent particles dried in step S1 in step S2 is 1.5-2:1; and the volume ratio of the FeSO4 solution to the biological crust adsorbent particles dried in step S2 in step S3 is 1-1.5:

1.

3. The method for preparing a precipitation-loaded slow-release carbon-based iron fertilizer as claimed in claim 1, characterized in that: The low-temperature drying temperature in step S1, step S2 and step S3 is 55-65°C.

4. The method for preparing a precipitation-loaded 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 biocrust particles with excess ferrous sulfate is 1:3-1:5, the low-temperature drying temperature in step S4 is 50-55° C., and the precipitated loaded slow-release carbon-based iron fertilizer in step S4 is filtered through a mesh to obtain a particle size of 2-3 mm.

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

5.

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