Silicon activated biochar and preparation method thereof

Abstract

The invention relates to silicon activated biochar and a preparation method thereof, and the preparation method comprises the following steps: S100: obtaining a raw material containing a silicon planting body, the silicon content of the raw material being 5% or above; s200, air-drying the raw materials obtained in the step S100, placing the air-dried raw materials in a carbonization furnace in an oxygen-free atmosphere, carbonizing the air-dried raw materials at 700 DEG C or below for 2-2.5 h, cooling the carbonized raw materials, and crushing and grinding the cooled raw materials to obtain carbonized raw materials; and S300, the C-Si mutual protection structure in the carbonized raw material obtained in the step S200 is destroyed through chemical modification or physical modification, silicon dissolution is promoted, silicon activated biochar is obtained, and the effective silicon content in the silicon activated biochar ranges from 100 mg / kg to 1000 mg / kg.

Description

Technical Field

[0001] The invention relates to the technical field of contaminated soil remediation and barren soil improvement, and in particular to silicon-activated biochar and a preparation method thereof. Background Art

[0002] Biochar is a carbon-rich solid product obtained by pyrolysis of waste biomass under anaerobic or anoxic conditions. It has the characteristics of high degree of aromatization, developed pore structure, rich surface functional groups, and high mineral nutrient content. Therefore, it is widely used in soil pollution remediation, water purification, soil improvement, crop yield increase, and carbon sequestration.

[0003] The waste of silicon-absorbing crops (such as rice husks, straw, etc.) contains a large amount of silicon. The biochar made from these raw materials has a high silicon content and is considered to be silicon-rich biochar. Studies have shown that silicon can reduce the absorption of heavy metals such as cadmium and arsenic in the soil by crops such as rice. As a beneficial element, silicon can promote plant growth and alleviate plant biological stress (such as pathogens, pests, etc.) and abiotic stress (such as salt damage, drought, flooding, high temperature, cold, nutrient imbalance, aluminum and heavy metals, etc.). However, the overall effective silicon content in rice fields is low. Using appropriate activation methods to increase the effective silicon content in biochar, and using the obtained silicon-activated biochar in cadmium-arsenic composite contaminated rice fields can not only passivate heavy metals such as cadmium and arsenic in the soil, but also increase the effective silicon content in silicon-deficient soils, ensure food security, and realize the resource utilization of agricultural waste. Summary of the invention

[0004] In view of the above analysis, an embodiment of the present invention aims to provide a silicon-activated biochar and a preparation method thereof, so as to solve at least one of the above problems.

[0005] In one aspect, the present invention provides a method for preparing silicon-activated biochar, comprising the following steps:

[0006] S100: obtaining a raw material containing phytoliths, wherein the silicon content of the raw material is greater than 5%;

[0007] S200: air-drying the raw material obtained in S100, placing it in a carbonization furnace in an oxygen-free atmosphere at a temperature below 700° C. for 2 to 2.5 hours, and then cooling it and crushing and grinding it to obtain the carbonized raw material;

[0008] S300: destroying the mutually protective structure of C-Si in the carbonized raw material obtained in S200 by chemical modification or physical modification, promoting silicon dissolution to obtain silicon-activated biochar, wherein the effective silicon content in the silicon-activated biochar is in the range of 100 to 1000 mg / kg.

[0009] Furthermore, the chemical modification in step S300 is oxidative modification.

[0010] Further, the operation of the oxidation modification is as follows:

[0011] S311: The carbonized raw material is placed in a strong oxidant solution, and after being water-bathed at 75-85°C for 5-6 hours, it is dried at 35-45°C to obtain silicon-activated biochar.

[0012] Furthermore, the strong oxidant is one of hydrogen peroxide, potassium permanganate and sodium hypochlorite.

[0013] Further, the concentration of hydrogen peroxide is 5% to 15%;

[0014] Each gram of carbonized raw material phase should be treated with 10 mL of hydrogen peroxide solution.

[0015] Furthermore, the physical modification in step S300 includes a dry-wet alternating modification method or a freeze-thaw cycle modification method.

[0016] Furthermore, the operation of the dry-wet alternating modification method is as follows:

[0017] S321: Adjust the water content of the carbonized raw materials with deionized water to 100% of the maximum water holding capacity, stir to evenly disperse the carbonized raw materials in the deionized water, culture at 20-25°C for 14-16 hours, and then dry at 55-65°C for 8-10 hours until the deionized water is completely dried, then rehydrate to 100% of the maximum water holding capacity, and stir to evenly disperse in the deionized water. The wet culture and drying last for 24 hours, which is recorded as one round of dry-wet alternation. Repeat 5-25 rounds and then dry and store.

[0018] Furthermore, the freeze-thaw cycle modification method is operated as follows:

[0019] S331: Adjust the water content of the carbonized raw material with deionized water to 100% of the maximum water holding capacity, stir to evenly disperse the carbonized raw material in the deionized water, freeze at -12 to -18°C for 14 to 16 hours, and then thaw at 20 to 25°C for 8 to 10 hours until it is completely thawed, then rehydrate to 100% of the maximum water holding capacity, and stir to evenly disperse in deionized water. The freezing and thawing process lasts for 24 hours, which is recorded as one freeze-thaw cycle. Repeat 10 to 30 cycles and then store in a dry state.

[0020] Further, in step S200, the carbonization furnace is filled with nitrogen, argon or carbon dioxide to form an oxygen-free environment;

[0021] The carbonization furnace was heated at a rate of 10 °C / min to the final target temperature.

[0022] On the other hand, the present invention provides a silicon-activated biochar prepared by the above-mentioned preparation method.

[0023] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0024] (1) The biochar prepared by the present invention has a high effective silicon content, which can greatly improve the absorption and utilization rate of silicon in the biochar, improve soil health, promote plant growth and development, and increase crop yield and quality;

[0025] (2) The biochar prepared by the present invention has good silicon release performance and can release silicon into the soil stably and long-term, thus avoiding silicon fertilizer leaching and ensuring the long-term environmental effect of biochar in the soil;

[0026] (3) The biochar prepared by the present invention is also a soil remediation agent. On the one hand, it has a uniform, small, and dense porous structure and can adsorb a variety of pollutants. On the other hand, it can change the occurrence form of pollutants by adjusting the pH value of the soil, thereby reducing the harm of pollution, for example, it can reduce the mobility and bioavailability of heavy metals.

[0027] (4) The biochar produced by the present invention is made from phytolith-rich biomass raw materials such as rice husks and straws. The raw materials are easily available and have a low acquisition cost. The preparation process is mature and easy to operate. It can be applied to silicon-deficient or contaminated soil after large-scale production. The overall use cost is low and it has a high degree of practical application possibility.

[0028] In the present invention, the above-mentioned technical solutions can also be combined with each other to achieve more preferred combination solutions. Other features and advantages of the present invention will be described in the subsequent description, and some advantages can become obvious from the description, or can be understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained through the contents particularly pointed out in the description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The drawings are only for the purpose of illustrating particular embodiments and are not to be considered limiting of the present invention. Like reference symbols denote like components throughout the drawings.

[0030] Figure 1 The SEM images of rice husk charcoal and silicon-activated biochar in [Example 1] to [Example 6] in the specific implementation manner, wherein (a) is a SEM image of rice husk charcoal at 300°C, (b) is a SEM image of silicon-activated biochar in [Example 1], (c) is a SEM image of silicon-activated biochar in [Example 2], (d) is a SEM image of silicon-activated biochar in [Example 3], (e) is a SEM image of rice husk charcoal at 400°C, (f) is a SEM image of silicon-activated biochar in [Example 4], (g) is a SEM image of silicon-activated biochar in [Example 5], and (h) is a SEM image of silicon-activated biochar in [Example 6];

[0031] Figure 2 The graphs are graphs of effective silicon content in rice husk charcoal and silicon-activated biochar in [Example 1] to [Example 6] in the specific implementation manner, wherein (a) uses 0.025M citric acid as the leaching solution, and (b) uses 1M acetic acid-sodium acetate as the leaching solution;

[0032] Figure 3 It is a line graph of the release of silicon in water from rice husk charcoal and silicon-activated biochar in [Example 1] to [Example 6] in a specific embodiment, wherein (a) is a graph of the release of endogenous silicon from rice husk charcoal at 300°C and 400°C; (b) is a line graph of the release of endogenous silicon from [Example 1] and [Example 4]; (c) is a line graph of the release of endogenous silicon from [Example 2] and [Example 5]; (d) is a line graph of the release of endogenous silicon from [Example 3] and [Example 6];

[0033] Figure 4 This is a graph of the effective silicon content in silicon-activated biochar in [Example 7] in a specific embodiment, wherein (a) uses 0.025M citric acid as the leaching solution, and (b) uses 1M acetic acid-sodium acetate as the leaching solution;

[0034] Figure 5 This is a diagram of the effective silicon content in silicon-activated biochar in the specific implementation method [Example 8], wherein (a) uses 0.025M citric acid as the extracting solution, and (b) uses 1M acetic acid-sodium acetate as the extracting solution. DETAILED DESCRIPTION

[0035] The preferred embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings, wherein the accompanying drawings constitute a part of the present invention and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not used to limit the scope of the present invention.

[0036] In the description of the embodiments of the present invention, it should be noted that, unless otherwise clearly specified and limited, the term "connected" should be understood in a broad sense, for example, it can be a fixed connection, or a detachable connection, or an integral connection, which can be a mechanical connection, or an electrical connection, which can be a direct connection, or can be indirectly connected through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0037] The terms "top", "bottom", "above", "lower", and "on" used throughout the description are relative to the relative positions of components of a device, such as the relative positions of the top and bottom substrates within a device. It is understood that devices are multifunctional regardless of their orientation in space.

[0038] The common working surface of the present invention can be a plane or a curved surface, can be inclined, or can be horizontal. For the convenience of description, the embodiment of the present invention is placed on a horizontal plane and used on the horizontal plane, and "high and low" and "up and down" are defined in this way.

[0039] A specific embodiment of the present invention discloses a method for preparing silicon-activated biochar, comprising the following steps:

[0040] S100: obtaining a raw material containing phytoliths, wherein the silicon content of the raw material is greater than 5%;

[0041] S200: air-drying the raw material obtained in S100, placing it in a carbonization furnace in an oxygen-free atmosphere at a temperature below 700° C. for 2 to 2.5 hours, and then cooling it and crushing and grinding it to obtain the carbonized raw material;

[0042] S300: destroying the mutually protective structure of C-Si in the carbonized raw material obtained in S200 by chemical modification or physical modification, promoting silicon dissolution to obtain silicon-activated biochar, wherein the effective silicon content in the silicon-activated biochar is in the range of 100 to 1000 mg / kg.

[0043] The C-Si mutually protecting structure in the carbonized raw material refers to a structure in which a layer of C and a layer of Si are superimposed on each other to protect each other in the carbonized raw material.

[0044] The silicon activated biochar prepared by the present invention has a high effective silicon content, and its endogenous silicon has a certain slow release property. After the silicon activated biochar is used for passivation and repair of soil contaminated by heavy metals such as cadmium and arsenic, it can gradually release silicon into the soil, increase the effective silicon content in the soil, regulate the migration and transformation of heavy metals in the soil-plant system, and promote crop growth.

[0045] In step S100, the phytoliths are called plant silicates, which refer to water-containing amorphous silicon dioxide particles formed by certain higher plants absorbing soluble silicon dioxide from soil moisture and then precipitating it inside or outside plant cells.

[0046] The raw materials are biomass materials rich in phytoliths, such as rice husks and straws, which are easy to obtain and have low economic costs. What is more worth mentioning is that as biomass rich in phytoliths, they do not need to be artificially modified or added with silicon elements in the later stage.

[0047] In step S200, the air-drying conditions of the raw materials are: natural ventilation at room temperature until air-dried.

[0048] The air-dried raw materials are placed in a carbonization furnace for carbonization. The carbonization furnace is filled with an inert atmosphere formed by nitrogen, argon or carbon dioxide to ensure that the preparation process is in an oxygen-free environment. Preferably, the nitrogen atmosphere flow rate is 0.1 L / min. Nitrogen is filled into the carbonization furnace to form an oxygen-free environment.

[0049] The pyrolysis temperature needs to be lower than 700 °C, and the carbonization furnace is increased at a rate of 10 °C / min to the final target temperature and then maintained for 2 h.

[0050] It should be noted that the carbonization process of the raw materials requires a high-purity nitrogen atmosphere. The main function of filling with high-purity nitrogen is to prevent oxygen from reacting with the carbonized material and avoid oxidation reactions during the pyrolysis process.

[0051] The raw material is cracked and carbonized in the carbonization furnace. After the cracking and carbonization are completed, the carbonization furnace is cooled to room temperature (i.e. 25±5°C), and then the carbonization furnace is opened to obtain the carbonized raw material, which is crushed and ground to make the particle size of the carbonized raw material less than 1mm. During the grinding process, it is necessary to ensure that the larger particles are broken, that is, the obtained carbonized raw material particles are small and there are no larger particles.

[0052] The air-dried raw materials are pyrolyzed and carbonized under relatively low temperature for a certain period of time under anaerobic conditions to form a solid material with high carbon content, high porosity, strong adsorption capacity and multiple uses. It can be used as a soil pollution remediation agent and improver, and can also play a role in carbon fixation.

[0053] The chemical modification in step S300 is carried out by oxidation modification, and the operation of the oxidation modification is as follows:

[0054] S311: placing the carbonized raw material into a strong oxidant solution, water bathing at 75-85° C. (preferably 80° C.) for 5-6 hours, and drying at 35-45° C. (preferably 40° C.) to obtain silicon-activated biochar.

[0055] The strong oxidant is one of the strong oxidizing compounds such as hydrogen peroxide, potassium permanganate, sodium hypochlorite, etc.

[0056] The concentration of hydrogen peroxide is 5% to 15%. The mixing ratio of the mass (in g) of the carbonized raw material (referred to as carbonized raw material) to the volume (in mL) of hydrogen peroxide is 1:10, that is, 10 mL of hydrogen peroxide solution is used for each gram of carbonized raw material, so that the carbonized raw material and the hydrogen peroxide solution should be fully mixed.

[0057] Preferably, the concentration of the hydrogen peroxide is 15%. Using a too high concentration of hydrogen peroxide may cause excessive oxidation of the carbonized raw material, resulting in collapse of the carbon skeleton structure and destruction of the porous structure, thereby affecting its adsorption performance.

[0058] Hydrogen peroxide solution, i.e., hydrogen peroxide, has strong oxidizing properties. In the process of fully contacting with the carbonized raw material, it can dissolve organic matter and other substances present in the carbonized raw material (part of the unstable organic matter attached to the surface of the carbon skeleton is oxidized by hydrogen peroxide and becomes small molecules or dissolved organic matter, thereby falling off the carbon skeleton). At a suitable concentration, it can make the carbon skeleton clearer and promote the further formation of a porous structure, thereby further improving its adsorption capacity for pollutants. The carbonized raw material prepared by the present invention using plants rich in phytoliths as raw materials can promote the further oxidation and rupture of the remaining phytoliths in the process of fully contacting with hydrogen peroxide. From a microscopic perspective, it has a destructive effect on the mutual protection of C-Si, making Si into a form that is easier to release and be used by organisms, thereby improving the biological effectiveness of its endogenous silicon.

[0059] The physical modification in step S300 may be carried out by a dry-wet alternating modification method or a freeze-thaw cycle modification method, wherein the operation of the dry-wet alternating modification method is as follows:

[0060] S321: Adjust the water content of the carbonized raw material with deionized water to 100% of the maximum water holding capacity (or immerse the carbonized raw material in water), stir to make the carbonized raw material evenly dispersed in the deionized water, incubate it at 20-25°C for 14-16 hours, and then dry it at 55-65°C for 8-10 hours until the deionized water is completely dried, then rehydrate it to 100% of the maximum water holding capacity, and stir to evenly disperse it in the deionized water. The wet incubation and drying last for 24 hours, which is recorded as one round of dry-wet alternation (one dry-wet alternation lasts 24 hours). Repeat 5-25 rounds and then dry and store.

[0061] Through the above-mentioned dry-wet alternating treatment, the carbonized raw material undergoes a certain degree of aging during the dry-wet alternating treatment, that is, a certain degree of oxidation occurs, and the oxidation effect destroys the mutual protection of C-Si.

[0062] Preferably, the number of rounds of alternating dry and wet is 10 times.

[0063] The operation of the freeze-thaw cycle modification method is as follows:

[0064] S331: Adjust the water content of the carbonized raw material with deionized water to 100% of the maximum water holding capacity (or immerse the carbonized raw material in water), stir to make the carbonized raw material evenly dispersed in the deionized water, freeze at -12 to -18°C for 14 to 16 hours, and then thaw at 20 to 25°C for 8 to 10 hours until it is completely thawed, then rehydrate to 100% of the maximum water holding capacity, and stir to evenly disperse in deionized water. The freezing and thawing last for 24 hours, which is recorded as one freeze-thaw cycle (one freeze-thaw cycle lasts 24 hours). Repeat 10 to 30 cycles and then dry and store.

[0065] Through the above freeze-thaw cycle treatment, the carbonized raw material undergoes a certain degree of aging during the freeze-thaw cycle treatment, that is, a certain degree of oxidation occurs, and the oxidation effect destroys the mutual protection of C-Si.

[0066] Preferably, the freeze-thaw cycle is performed 25 times.

[0067] Preferably, when step S300 adopts chemical modification, the carbonization temperature adopted in step S200 is 300-400° C. When step S300 adopts physical modification, the carbonization temperature adopted in step S200 is 600-700° C.

[0068] The raw materials of the present invention are easy to obtain and operate, and can be used for silicon-deficient or polluted farmland. It can not only repair the polluted farmland, but also provide effective silicon to the soil more effectively and for a long time. It is also an effective way to recycle agricultural and forestry wastes.

[0069] The silicon-activated biochar of the present invention can play a certain adsorption role on pollutants in the soil as a soil pollution remediation agent. At the same time, it can change the occurrence form of pollutants by adjusting the pH value of the soil, thereby reducing the harm of pollution. As a soil conditioner, it is regarded as a new opportunity for carbon fixation and mitigation of global warming, and is also a strategy for improving soil health and productivity.

[0070] The silicon activated biochar of the present invention releases effective silicon into the soil, which has a certain effect on the morphological change of pollutants. It can also participate in many physiological activities and metabolic effects of plants, promote the formation, development and robust growth of plant organs, improve the leaf attachment mode and canopy structure, etc. At the same time, it can improve the mechanical strength, light interception and resistance to various forms of abiotic and biotic stresses of plants, thereby improving yield and quality.

[0071] [Example 1]: A method for preparing silicon-activated biochar by chemical modification is provided, comprising the following steps:

[0072] S100: obtaining rice husk raw materials;

[0073] S200: After the rice husk raw material is air-dried, it is placed in a carbonization furnace for carbonization. The carbonization furnace is an inert atmosphere formed by nitrogen, and the flow rate of the nitrogen atmosphere is 0.1L / min. The carbonization furnace is initially increased to 300°C at a rate of 10°C / min, and then maintained for 2h. After the cracking and carbonization is completed, the carbonization furnace is first cooled to room temperature (i.e., 25±5°C), and then the carbonization furnace is opened to obtain carbonized rice husk (i.e., carbonized rice husk raw material, referred to as rice husk charcoal), and the rice husk charcoal is crushed and ground;

[0074] S300: The obtained rice husk charcoal (g) and 5% hydrogen peroxide (mL) were fully mixed at a mixing ratio of 1:10, and then placed in a water bath at 80° C. for 6 h, and then dried at 40° C. to obtain silicon-activated biochar using rice husk as raw material.

[0075] [Example 2]: Different from [Example 1], the concentration of the hydrogen peroxide solution is 10%, and the other conditions are the same.

[0076] [Example 3]: Different from [Example 1], the concentration of the hydrogen peroxide solution is 15%, and the other conditions are the same.

[0077] [Example 4]: Different from [Example 1], the carbonization temperature is 400°C, and the other conditions are the same.

[0078] [Example 5]: Different from [Example 1], the carbonization temperature is 400°C, the concentration of the hydrogen peroxide solution is 10%, and the other conditions are the same.

[0079] [Example 6]: Different from [Example 1], the carbonization temperature is 400°C, the concentration of the hydrogen peroxide solution is 15%, and the other conditions are the same.

[0080] The total silicon and effective silicon content in the silicon-activated biochar obtained from [Example 1] to [Example 6], as well as the release pattern of effective silicon, are analyzed. The results are shown in Table 1. Figure 1 to Figure 3 shown.

[0081] Table 1 - Total silicon content in rice husk raw materials and silicon-activated biochar obtained from [Example 1] to [Example 6]

[0082]

[0083]

[0084] It can be seen from Table 1 that the total silicon content of rice husk raw material can reach 10%, which shows that it is a biomass raw material rich in phytoliths. The total silicon content of the above six examples can reach more than 20%, and the total silicon content of rice husk charcoal with a preparation temperature of 400°C can reach 30%, which can be determined to be a silicon-rich biochar.

[0085] Table 2-pH of rice husk charcoal and silicon-activated biochar obtained from [Example 1] to [Example 6]

[0086] sample pH 300℃ Rice Husk Charcoal 7.87±0.16 Example 1 4.26±0.09 Example 2 3.23±0.03 Example 3 2.68±0.01 400℃ Rice Husk Charcoal 8.92±0.29 Example 4 4.49±0.02 Example 5 3.36±0.04 Example 6 2.74±0.01

[0087] As can be seen from Table 2, rice husk charcoal is neutral or weakly alkaline, and the rice husk charcoal treated by the above methods is acidic, and its pH can affect the soil pH, thereby further changing the occurrence form of pollutants by adjusting the soil pH value.

[0088] Figure 1 The microscopic morphology of rice husk charcoal and silicon-activated biochar (SEM image) shows that there are a large number of regular and uniform porous structures in rice husk charcoal. The surface morphology changes after oxidation modification. Many particles are broken, and the broken small particles are attached to the surface of larger biochar particles. This phenomenon becomes more obvious with the increase of oxidation degree. At the same time, the carbon skeleton gradually becomes blurred with the increase of oxidation degree.

[0089] from Figure 2 It can be seen that the effective silicon content of the silicon-activated biochar of the present invention is higher than that of the rice husk charcoal that has not been oxidatively modified, and as the concentration of the hydrogen peroxide solution used continues to increase, the effective silicon content becomes higher and higher. Figure 2 The two leaching solutions (i.e., citric acid leaching and acetic acid-sodium acetate leaching) were used to extract the effective silicon, and the obtained change trends were basically consistent. For the experiment of using 0.025M citric acid to extract the effective silicon, the biological effectiveness of silicon in Examples 3 and 6 was the greatest, increasing by 74.1% and 126.0% respectively; for the experiment of using 1M acetic acid-sodium acetate to extract the effective silicon, the biological effectiveness of silicon in Examples 3 and 6 was also the greatest, increasing by 166.1% and 333.3% respectively.

[0090] from Figure 3 The release rate of silicon in the biochar sample was measured by batch desorption method. 0.05g of biochar sample was added to 50mL of 0.01M CaCl2 solution and shaken at 150rpm at 25°C for 28 days. Three parallel groups of each sample were set. The suspension was collected on the 1st and 4th day and every 4 days thereafter to measure the silicon content. It can be seen that the release rate of endogenous silicon in the silicon-activated biochar of the present invention is greatly reduced, and the sustained-release performance is significantly improved. Specifically, by Figure 3 (a) It can be seen that the release of endogenous silicon in rice husk charcoal increases rapidly during the period of 0 to 12 days, gradually becomes stable around 12 to 14 days, and then basically stabilizes at around 7 mg / g. Figure 3 (b), (c) and (d) show that the release of endogenous silicon in silicon-activated biochar is significantly reduced, and the overall release trend is uniform, and the release rate still tends to increase after 28 days (1.62-2.43 mg / g).

[0091] It can be seen from the above that the silicon-activated biochar obtained by chemical modification using rice husk as raw material in the present invention has greatly increased the biological effectiveness and sustained release performance of endogenous silicon.

[0092] [Example 7]: A method for preparing silicon-activated biochar by alternating dry-wet modification is provided, comprising the following steps:

[0093] S100: obtaining rice husk raw materials;

[0094] S200: After the rice husk raw material is air-dried, it is placed in a carbonization furnace for carbonization. The carbonization furnace is an inert atmosphere formed by nitrogen, and the flow rate of the nitrogen atmosphere is 0.1L / min. The carbonization furnace is initially increased to 600°C at a rate of 10°C / min, and then maintained for 2h. After the cracking and carbonization is completed, the carbonization furnace is first cooled to room temperature (i.e., 25±5°C), and then the carbonization furnace is opened to obtain carbonized rice husk (i.e., carbonized rice husk raw material, referred to as rice husk charcoal), and the rice husk charcoal is crushed and ground;

[0095] S300: The obtained rice husk charcoal is adjusted to have a water content of 100% of its maximum water holding capacity with deionized water, and the rice husk charcoal is stirred to be evenly dispersed in the deionized water, and is cultured at 25°C for 16 hours, and then dried at 65°C for 8 hours until the deionized water is completely dried, and then rehydrated to 100% of the maximum water holding capacity, and the rice husk charcoal is stirred to be evenly dispersed in the deionized water, which lasts for 24 hours, which is recorded as one round of dry-wet alternation. After 25 rounds are repeated, the biochar is dried and stored to obtain silicon-activated biochar obtained by dry-wet alternation modification.

[0096] Analysis [Example 7] The variation of total silicon and effective silicon content in silicon activated biochar was obtained. The results are shown in Table 3 and Figure 4 shown.

[0097] Table 3 - Total silicon content in rice husk raw materials and silicon-activated biochar obtained from [Example 7]

[0098] sample Total silicon / % Rice husk raw materials 10.07±0.21 Example 7 40.50±0.14

[0099] It can be seen from Table 3 that the total silicon content of the rice husk raw material is 10%, and the total silicon content of the silicon-activated biochar obtained in Example 7 reaches about 40%, which can be determined to be a silicon-rich biochar.

[0100] from Figure 4 It can be seen that the effective silicon content of the silicon-activated biochar obtained in Example 7 increased to varying degrees. This example used two leaching solutions to extract effective silicon, and the obtained change trends were basically consistent. For the experiment of using 0.025M citric acid to extract effective silicon (such as Figure 4 (a) shows that the bioavailability of silicon increased the most when the dry-wet alternation was carried out for the 10th round, increasing by 17.8%. For the experiment of using 1M acetic acid-sodium acetate to extract effective silicon (as shown in Figure 4 (b) shows that the bioavailability of silicon increased the most when the dry-wet alternation was carried out for the 25th time, increasing by 33.6%.

[0101] [Example 8]: A method for preparing silicon-activated biochar by freeze-thaw cycle modification is provided, comprising the following steps:

[0102] S100: obtaining rice husk raw materials;

[0103] S200: After the rice husk raw material is air-dried, it is placed in a carbonization furnace for carbonization. The carbonization furnace is an inert atmosphere formed by nitrogen, and the flow rate of the nitrogen atmosphere is 0.1L / min. The carbonization furnace is initially increased to 600°C at a rate of 10°C / min, and then maintained for 2h. After the cracking and carbonization is completed, the carbonization furnace is first cooled to room temperature (i.e., 25±5°C), and then the carbonization furnace is opened to obtain carbonized rice husk (i.e., carbonized rice husk raw material, referred to as rice husk charcoal), and the rice husk charcoal is crushed and ground;

[0104] S300: The obtained rice husk charcoal is adjusted to have a moisture content of 100% of its maximum water holding capacity with deionized water, the rice husk charcoal is stirred to be evenly dispersed in the deionized water, frozen at -18°C for 16 hours, and then thawed at 25°C for 8 hours, and then the rice husk charcoal is stirred to be evenly dispersed in the deionized water, which lasts for 24 hours, which is recorded as one freeze-thaw cycle. After 25 cycles are repeated, the charcoal is dried and stored to obtain silicon-activated biochar obtained by freeze-thaw cycle modification.

[0105] Analysis [Example 8] The variation of total silicon and effective silicon content in silicon activated biochar was obtained. The results are shown in Table 4 and Figure 5 shown.

[0106] Table 4 - Total silicon content in rice husk raw materials and silicon-activated biochar obtained from [Example 8]

[0107] sample Total silicon / % Rice husk raw materials 10.07±0.21 Example 8 40.50±0.14

[0108] It can be seen from Table 4 that the total silicon content of the rice husk raw material is 10%, and the total silicon content of the silicon-activated biochar obtained in Example 8 reaches about 40%, which can be determined to be a silicon-rich biochar.

[0109] from Figure 5 It can be seen that the effective silicon content of the silicon-activated biochar obtained in Example 8 increased to varying degrees. This example used two leaching solutions to extract effective silicon, and the obtained change trends were basically consistent. The results of the two leaching experiments showed that the degree of improvement in the bioavailability of silicon was greater when the freeze-thaw cycle reached the 25th round than that of other rounds. For the experiment of using 1M acetic acid-sodium acetate to extract effective silicon, it increased by 19.3%.

[0110] It should be noted that Figure 2 , Figure 4 and Figure 5 a, b, ab, c, and d above the error bars represent significant differences among different treatments.

[0111] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for preparing silicon-activated biochar, characterized in that: The following steps are involved: S100: obtaining a raw material containing phytoliths, wherein the silicon content of the raw material is greater than 5%; S200: air-drying the raw material obtained in S100, placing it in a carbonization furnace in an oxygen-free atmosphere at a temperature below 700° C. for 2 to 2.5 hours, and then cooling it and crushing and grinding it to obtain the carbonized raw material; S300: destroying the mutually protective structure of C-Si in the carbonized raw material obtained in S200 by chemical modification or physical modification, promoting silicon dissolution to obtain silicon-activated biochar, wherein the effective silicon content in the silicon-activated biochar is in the range of 100 to 1000 mg / kg.

2. The preparation method according to claim 1, characterized in that: The chemical modification in step S300 is oxidative modification.

3. The preparation method according to claim 2, characterized in that: The operation of the oxidation modification is as follows: S311: The carbonized raw material is placed in a strong oxidant solution, and after being water-bathed at 75-85°C for 5-6 hours, it is dried at 35-45°C to obtain silicon-activated biochar.

4. The preparation method according to claim 3, characterized in that: The strong oxidant is one of hydrogen peroxide, potassium permanganate and sodium hypochlorite.

5. The preparation method according to claim 4, characterized in that: The concentration of hydrogen peroxide is 5% to 15%; Each gram of carbonized raw material phase should be treated with 10 mL of hydrogen peroxide solution.

6. The preparation method according to claim 1, characterized in that: The physical modification in step S300 includes a dry-wet alternating modification method or a freeze-thaw cycle modification method.

7. The preparation method according to claim 6, characterized in that: The operation of the dry-wet alternating modification method is as follows: S321: Adjust the water content of the carbonized raw materials with deionized water to 100% of the maximum water holding capacity, stir to evenly disperse the carbonized raw materials in the deionized water, culture at 20-25°C for 14-16 hours, and then dry at 55-65°C for 8-10 hours until the deionized water is completely dried, then rehydrate to 100% of the maximum water holding capacity, and stir to evenly disperse in the deionized water. The wet culture and drying last for 24 hours, which is recorded as one round of dry-wet alternation. Repeat 5-25 rounds and then dry and store.

8. The preparation method according to claim 6, characterized in that: The operation of the freeze-thaw cycle modification method is as follows: S331: Adjust the water content of the carbonized raw material with deionized water to 100% of the maximum water holding capacity, stir to evenly disperse the carbonized raw material in the deionized water, freeze at -12 to -18°C for 14 to 16 hours, and then thaw at 20 to 25°C for 8 to 10 hours until it is completely thawed, then rehydrate to 100% of the maximum water holding capacity, and stir to evenly disperse in deionized water. The freezing and thawing process lasts for 24 hours, which is recorded as one freeze-thaw cycle. Repeat 10 to 30 cycles and then store in a dry state.

9. The preparation method according to any one of claims 1 to 8, characterized in that: In step S200, the carbonization furnace is filled with nitrogen, argon or carbon dioxide to form an oxygen-free environment; The carbonization furnace was heated at a rate of 10 °C / min to the final target temperature.

10. A silicon activated biochar, characterized in that: The method is prepared by any one of claims 1 to 9.

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