Agricultural rice hull / straw carbon-based silicon fertilizer and preparation method thereof

Abstract

The invention provides an agricultural rice hull / straw carbon-based silicon fertilizer and a preparation method thereof.The preparation method comprises the steps that S1, smashed straw and / or rice hull are put into a reaction kettle, water and potassium hydroxide are added, a pyrolytic reaction is conducted in the anaerobic environment with the temperature of 200-250 DEG C and the pressure of 0.1-0.5 MPa, cooling is conducted to the room temperature after the reaction is completed, and blended biochar and an organic solution I containing potassium silicate and biological vinegar are obtained; s2, sulfuric acid is added into the reaction kettle, then potassium silicate in the organic solution I makes contact with the sulfuric acid in the constant-temperature environment of 30-50 DEG C, then a double decomposition reaction is carried out, and water-soluble metasilicic acid and potassium sulfate are generated; and after the double decomposition reaction is finished, cooling to room temperature to obtain the carbon-based silicon fertilizer consisting of the blended biochar and an organic solution II containing water-soluble metasilicic acid, potassium sulfate and biological vinegar. According to the preparation method disclosed by the invention, original fertilizer and soil improvement characteristics of the biochar are reserved, and meanwhile, the characteristic of facilitating absorption of monatomic silicon by plants is increased, so that the additional value of the biomass charcoal-based fertilizer is remarkably improved.

Description

Technical Field

[0001] The invention relates to a silicon fertilizer, in particular to an agricultural rice husk / straw carbon-based silicon fertilizer and a preparation method thereof. Background Art

[0002] With the rapid development of agriculture in my country, a large amount of agricultural waste is generated every year. At present, there is a lack of effective resource recycling methods for agricultural waste in rural my country. Every year, a large amount of rice husks and straw are burned from south to north, forming smoke and generating air pollution. In recent years, due to the increasingly serious air pollution with PM2.5 as an indicator, the random burning method has been gradually banned. However, how to reasonably utilize agricultural waste such as straw and rice husks is still a dilemma.

[0003] At present, one of the effective treatment methods for agricultural wastes such as rice husks and straws is to convert them into biochar by pyrolysis, and then mix them with substances containing nitrogen, phosphorus, potassium, etc. to prepare conventional carbon-based fertilizers. As a renewable carbon-based material, the preparation process of biochar involves high-temperature pyrolysis of biological residues under anaerobic conditions. The resulting biochar is a black, fluffy solid substance with fine particles and light texture. It is insoluble, stable, highly aromatic and rich in carbon. Biochar can not only be used to improve soil and increase crop yields, but also is one of the effective means to reduce carbon emissions. By applying it to agricultural practices such as reduced and no-till systems, cover crops, green manures, rotational grazing, and composting, biochar has demonstrated its significant ability to reduce carbon emissions. In addition, biochar can promote the stabilization of carbon in the soil and increase biological activity.

[0004] However, conventional charcoal-based fertilizers do not take into account different types of biomass raw materials, such as wood raw materials and grass raw materials, which contain different amounts of silicon, and this element is very important for plant growth. The role of silicon in plant growth is mainly reflected in the fact that silicon participates in the formation of plant cell walls, which can improve plant photosynthesis and transpiration, improve plant stress resistance, and also promote the absorption of other nutrients. Compared with wood, agricultural waste such as straw and rice husks has a high ash (inorganic matter) content (mass fraction reaches 4%-20%), and the main content is silicon (SiO2), accounting for 65%-95% of the mass fraction of straw ash. Since the traditional pyrolysis method does not specially treat or retain the silicon element in biomass, the effectiveness of silicon in the final charcoal-based fertilizer cannot be guaranteed, thereby limiting the fertilizer's ability to support plant silicon demand. Summary of the invention

[0005] In view of the problem that conventional carbon-based fertilizers cannot effectively utilize silicon in rice husks and straws, the present invention provides an agricultural rice husk / straw carbon-based silicon fertilizer and a preparation method thereof. The method retains the original fertilizer and soil improvement properties of biochar and adds properties that are beneficial to plant absorption of elemental silicon, thereby significantly increasing the added value of biomass carbon-based fertilizers.

[0006] The present invention achieves the above technical objectives through the following technical means.

[0007] A method for preparing agricultural rice husk / straw carbon-based silicon fertilizer comprises the following steps:

[0008] S1: Put the crushed straw and / or rice husk into a reactor, add water and potassium hydroxide, and then carry out pyrolysis reaction in an oxygen-free environment at 200-250° C. and 0.1-0.5 MPa. After the reaction is completed, cool to room temperature to obtain a blended biochar and an organic solution I containing potassium silicate and biological vinegar;

[0009] S2: Sulfuric acid is added into the reactor, and then under a constant temperature environment of 30-50°C, potassium silicate in the organic solution I contacts with sulfuric acid to undergo double decomposition reaction to generate water-soluble metasilicic acid and potassium sulfate; after the double decomposition reaction is completed, the solution is cooled to room temperature to obtain a carbon-based silicon fertilizer consisting of blended biochar and an organic solution II containing water-soluble metasilicic acid, potassium sulfate and biological vinegar.

[0010] Furthermore, in step S1, the ratio of the added amount of the straw and / or rice husk to the water is 100g:(500-1000ml).

[0011] Further, in step S1, the pyrolysis reaction is:

[0012] SiO2+2KOH→K2SiO3+H2O

[0013] Here, the theoretical amount of potassium hydroxide required to completely decompose SiO2 in straw and rice husk is assumed to be M1, and the actual amount of potassium hydroxide added is M≤M1.

[0014] Furthermore, in step S1, the straw and / or rice husk is crushed to a particle size of 50 to 200 meshes.

[0015] Furthermore, in step S1, the pyrolysis reaction lasts for 2 to 5 hours.

[0016] Furthermore, in step S1, the temperature is increased at a heating rate of 3 to 5°C / min.

[0017] Further, in step S2, the metathesis reaction is:

[0018] K2SiO3+H2SO4→K2SO4+H2SiO3

[0019] Here, assuming that the theoretical amount of sulfuric acid required to completely decompose potassium silicate is m1, the actual amount of sulfuric acid added is m≤m1.

[0020] Furthermore, in step S2, the double decomposition reaction lasts for 3 to 5 hours.

[0021] Agricultural rice husk / straw carbon-based silicon fertilizer prepared according to any of the above preparation methods.

[0022] Furthermore, the specific surface area of ​​the blended biochar in the agricultural rice husk / straw carbon-based silicon fertilizer is 200 to 400 m 2 / g, the silicon element in organic solution II exists in the form of water-soluble metasilicic acid.

[0023] The beneficial effects of the present invention are as follows:

[0024] 1. The present invention utilizes a pyrolysis reaction to convert silicon dioxide in rice husks and straw into potassium silicate, and then utilizes sulfuric acid to convert potassium silicate into a water-soluble metasilicic acid in a form that can be utilized by plants, thereby significantly improving the bioavailability of silicon and making it easier for plants to absorb and utilize it.

[0025] 2. The water-soluble metasilicic acid in the present invention can not only be quickly absorbed by the plant root system, but also has obvious antibacterial and disease prevention effects, can enhance the disease resistance of plants and reduce the infection of pathogens.

[0026] 3. The sulfuric acid in the present invention can not only convert potassium silicate into water-soluble metasilicic acid, but also increase the specific surface area of ​​the blended biochar, so that the blended biochar has excellent water and fertilizer storage capacity, which can prevent the rapid loss of liquid fertilizer in practical applications and further enhance the plant's absorption characteristics of elements such as potassium and silicon in liquid fertilizer.

[0027] 4. The potassium hydroxide in the present invention can not only convert silicon dioxide into potassium silicate, but also, as a strong base, can form more micropores and mesopores through etching under hydrothermal conditions, thereby increasing the specific surface area and porosity of the blended biochar, enhancing, and further improving the adsorption capacity and water and fertilizer storage capacity of the blended biochar. At the same time, the presence of potassium hydroxide can increase the number of functional groups on the surface of the blended biochar, and improve the surface activity and adsorption capacity of the blended biochar.

[0028] 5. The present invention can promote the formation of silicified cells by promoting the effective absorption of silicon in carbon-based silicon fertilizer by plants, thereby thickening the cell walls of the crop surface, making the stems and leaves more upright, and helping to improve the efficiency of leaf photosynthesis. Silicified cells can also effectively regulate the opening and closing of crop stomata and water transpiration, thereby enhancing the crop's resistance to drought, dry hot winds, and low temperatures. On the other hand, it can enhance the oxidation capacity of plant roots, prevent premature aging and rot of the roots, improve the crop's resistance to lodging, and effectively prevent and control the pollution of heavy metals such as cadmium to crops. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is the GCMS spectrum characterizing the organic solution I described in the present invention.

[0030] Figure 2 These are the XRD spectra of potassium silicate and potassium sulfate in comparative experiments 1 and 2.

[0031] Figure 3 (a) is a SEM image of the surface of the blended biochar before the double decomposition reaction described in the embodiment of the present invention.

[0032] Figure 3 (b) is a SEM image of the surface of the blended biochar after the double decomposition reaction described in the embodiment of the present invention. DETAILED DESCRIPTION

[0033] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments, but the protection scope of the present invention is not limited thereto.

[0034] The method for preparing the agricultural rice husk / straw carbon-based silicon fertilizer described in this embodiment comprises the following steps:

[0035] S1: 500g of straw and 500g of rice husk were crushed to a particle size of 100 mesh and then put into a reactor, 6L of distilled water and 160g of potassium hydroxide were added, and pyrolysis reaction was carried out at 220°C and 0.5MPa in an oxygen-free environment for 3h. After the reaction was completed, it was cooled to room temperature to obtain blended biochar and an organic solution I containing potassium silicate and biological vinegar. The blended biochar was taken out, washed, filtered, and dried, and the mass of the blended biochar was 486.5g, that is, the carbon yield was 48.65%.

[0036] The pyrolysis reaction is:

[0037] SiO2+2KOH→K2SiO3+h2O

[0038] The amount of potassium hydroxide added in the above step S1 needs to be calculated based on the silicon content in rice husks and straws, and the specific process is as follows: First, the silicon content in straws and rice husks is 4.6% and 3.8% respectively according to ICPMS, so that the total mass of silicon in straws and rice husks is calculated to be 42g, and the molecular weight of silicon dioxide is 60g / mol. Since the mass fraction of silicon in silicon dioxide is 28 / 60, the total mass of silicon dioxide = 42g ÷ (28 / 60) = 90g. Then calculate the number of moles of silicon dioxide = 90 / 60 = 1.5mol, so the number of moles of potassium hydroxide required = 1.5*2 = 3mol. Finally, according to the molecular weight of potassium hydroxide, it is 56g / mol, so that the mass of potassium hydroxide required is calculated to be 3*56 = 168g. In order to ensure that the potassium hydroxide input is fully reacted to avoid the residual potassium hydroxide from affecting the subsequent reaction, the amount of potassium hydroxide added in this embodiment should not exceed the maximum mass of potassium hydroxide required for the complete reaction (i.e. 168g), and 160g is taken here.

[0039] The obtained organic solution I containing potassium silicate and biological vinegar was subjected to XRF and GCMS quantitative detection. Figure 1 Table 1 is the GCMS spectra of organic solution I described in this embodiment. Figure 1 Qualitative table of the spectra shown.

[0040] Table 1 GCMS characterization of organic solution I Qualitative

[0041]

[0042]

[0043] Table 2 is the XRF quantitative analysis table of carbon, potassium, silicon and nitrogen oxides in organic solution I, and Table 3 is the XRF quantitative analysis table of silicon, potassium, sulfur and phosphorus in organic solution I. It can be seen from the two figures that organic solution I is rich in potassium, silicon, nitrogen and other elements, which can provide the nutrients required by various plants and improve crop yield and quality.

[0044] Table 2 XRF quantitative analysis of carbon, potassium, silicon and nitrogen oxides in organic solution I

[0045] Oxide Quantitative analysis% <![CDATA[CO2]]> 57.25 <![CDATA[K2O]]> 21.27 <![CDATA[SiO2]]> 15.74 <![CDATA[N2O5]]> 5.74

[0046] Table 3 XRF quantitative analysis of silicon, potassium, sulfur and phosphorus in organic solution I

[0047] Single substance Quantitative analysis mass% Si 15.89 K 61.30 S 22.68 P 0.25

[0048] In order to clarify whether the above pyrolysis reaction can produce potassium silicate and eliminate the interference of biomass crude liquid, this embodiment also conducted a comparative experiment 1. The only difference from the above step S1 is that potassium hydroxide was not added before the pyrolysis reaction, and then the blended biochar obtained after the pyrolysis reaction was taken out, washed, filtered, and dried before reacting with potassium hydroxide. Figure 2 The middle part is the XRD spectrum of potassium silicate in comparative experiment 1, which shows that the silicon dioxide attached to the pores of the blended biochar reacts with potassium silicate to generate potassium silicate, which verifies that the above-mentioned pyrolysis reaction can generate potassium silicate.

[0049] S2: Continue to add 85 ml of concentrated sulfuric acid to the reactor, keep it warm at a constant temperature of 50°C for 5 hours, and the potassium silicate in the organic solution I will undergo a double decomposition reaction after contacting with sulfuric acid to generate water-soluble metasilicic acid and potassium sulfate. After the double decomposition reaction is completed, cool to room temperature to obtain a carbon-based silicon fertilizer consisting of blended biochar and an organic solution II containing water-soluble metasilicic acid, potassium sulfate and biological vinegar. The double decomposition reaction is:

[0050] K2SiO3+H2SO4→k2SO4+H2SiO3

[0051] In order to clarify whether the above double decomposition reaction can generate potassium sulfate and eliminate the interference of biological vinegar, this embodiment also conducted a comparative experiment 2, in which the biological vinegar in the organic solution I was filtered out, and the blended biochar and potassium silicate mixture without biological vinegar was reacted with concentrated sulfuric acid under the same conditions in step S2. Figure 2 The other part is the XRD spectrum of potassium sulfate in comparative experiment 2. It can be seen from the figure that potassium sulfate is formed, which verifies that the above double decomposition reaction can generate potassium sulfate. At the same time, the mixed solution of water-soluble metasilicic acid and potassium sulfate is left to stand for a week, and no metasilicic acid is precipitated to form polysilicic acid or silicon dioxide, both of which are extremely insoluble in water, which shows that the carbon-based silicon fertilizer in this embodiment has good stability and can be stored for a long time without being easily deteriorated.

[0052] Figure 3 (a) is a SEM image of the surface of the blended biochar before the metathesis reaction described in this example, Figure 3 (b) is a SEM image of the surface of the blended biochar after the double decomposition reaction described in this embodiment. It can be seen from the figure that the addition of sulfuric acid reaction can break the surface of the blended biochar, thereby increasing the specific surface area of ​​the blended biochar. In this embodiment, the specific surface area of ​​the blended biochar increases from 10m 2 / g increased to 289m 2 / g.

[0053] Table 4 is a comparison table of pH values ​​of biochar and organic solution II blended in the carbon-based silicon fertilizer described in this embodiment. It can be seen from the table that the organic solution II in this embodiment is weakly acidic, particularly suitable for alkaline soil, and has the function of balancing the pH value of the soil.

[0054] Table 4 Comparison of pH values ​​of blended biochar and organic solution II in carbon-based silicon fertilizer

[0055] pH Blended Biochar 5.83 Organic Solution II 3.26

[0056] After the double decomposition reaction, there is no need to filter and separate the blended biochar and organic solution II. They can be directly applied to the soil or sprayed on the leaves, which is easy for roots and leaves to absorb. By converting silicon into water-soluble metasilicic acid that can be used by plants, the biological effectiveness of silicon is significantly improved, making it easier for plants to absorb and use. At the same time, by increasing the specific surface area of ​​the blended biochar (dual-effect modification of potassium hydroxide and sulfuric acid), the fertilizer storage capacity of the blended biochar is improved to avoid its rapid loss, thereby further enhancing the plant's absorption characteristics of various elements including silicon. After effectively absorbing sufficient silicon, plants can significantly improve their crop resistance. The specific mechanism can be analyzed from the aspects of physical action, chemical action, molecular action and soil microenvironment action. From the perspective of plants, first of all, silicon provides mechanical and physical barriers to plants. Silicon participates in the formation of plant cell walls. The cell wall is a barrier for plants to develop resistance. After adding silicon, a silicified cell layer can be formed on the leaf epidermis. The silicon deposited in the leaf epidermis forms a thick wall to resist external coercion. This is passive defense. At the same time, silicon can also actively induce plants to produce biochemical resistance. After adding silicon, plants can produce a large amount of secondary metabolites for defense, just like buying insurance for plants. In addition, silicon can also stimulate the expression of disease-resistant related genes at the molecular level. From the perspective of soil, silicon can change the physical and chemical properties of soil, affect the community structure of soil microorganisms, and induce roots to produce specific secretions.

[0057] The embodiments are preferred implementations of the present invention, but the present invention is not limited to the above-mentioned implementations. Any obvious improvements, substitutions or modifications that can be made by those skilled in the art without departing from the essential content of the present invention belong to the protection scope of the present invention.

Claims

1. A method for preparing agricultural rice husk / straw carbon-based silicon fertilizer, characterized in that: The following steps are involved: S1: Put the crushed straw and / or rice husk into a reactor, add water and potassium hydroxide, and then carry out pyrolysis reaction in an oxygen-free environment at 200-250° C. and 0.1-0.5 MPa. After the reaction is completed, cool to room temperature to obtain a blended biochar and an organic solution I containing potassium silicate and biological vinegar; S2: Sulfuric acid is added into the reactor, and then under a constant temperature environment of 30-50°C, potassium silicate in the organic solution I contacts with sulfuric acid to undergo double decomposition reaction to generate water-soluble metasilicic acid and potassium sulfate; after the double decomposition reaction is completed, the solution is cooled to room temperature to obtain a carbon-based silicon fertilizer consisting of blended biochar and an organic solution II containing water-soluble metasilicic acid, potassium sulfate and biological vinegar.

2. The preparation method according to claim 1, characterized in that: In step S1, the ratio of the added amount of the straw and / or rice husk to the water is 100g:(500-1000ml).

3. The preparation method according to claim 1, characterized in that: In step S1, the pyrolysis reaction is: SiO2+2KOH→K2SiO3+H2O Here, assuming that the theoretical amount of potassium hydroxide required to completely decompose SiO2 in straw and rice husk is M1, the actual amount of potassium hydroxide added is M≤M1.

4. The preparation method according to claim 1, characterized in that: In step S1, the straw and / or rice husk is crushed to a particle size of 50 to 200 meshes.

5. The preparation method according to claim 1, characterized in that: In step S1, the pyrolysis reaction lasts for 2 to 5 hours.

6. The preparation method according to claim 1, characterized in that: In step S1, the temperature is increased at a heating rate of 3 to 5°C / min.

7. The preparation method according to claim 1, characterized in that: In step S2, the metathesis reaction is: K2SiO3+K2SO4→K2SO4+H2SiO3 Here, assuming that the theoretical amount of sulfuric acid required to completely decompose potassium silicate is m1, the actual amount of sulfuric acid added is m≤m1.

8. The preparation method according to claim 1, characterized in that: In step S2, the metathesis reaction lasts for 3 to 5 hours.

9. Agricultural rice husk / straw carbon-based silicon fertilizer prepared according to the preparation method of any one of claims 1 to 8.

10. The agricultural rice husk / straw carbon-based silicon fertilizer according to claim 8, characterized in that: The specific surface area of ​​the blended biochar in the agricultural rice husk / straw carbon-based silicon fertilizer is 200 to 400 m 2 / g, the silicon element in organic solution II exists in the form of water-soluble metasilicic acid.

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