Method and application for preparing silicon-containing super-mineral-source potassium humate by using rice husk

Abstract

The present invention belongs to the technical field of treatment and resource utilization of agricultural and forestry solid wastes, and discloses a method for preparing silicon-containing super-mineral-source potassium humate from rice husks and its application. The preparation method is as follows: using a metal ion solution as a precursor, adding an alkali and a dispersant, and preparing a nano-metal oxide catalyst through a hydrothermal reaction. Then, mixing it with pretreated rice husks and a stabilizer, and performing a calcination treatment at 180-400 °C to obtain a calcined product; then stirring and mixing the calcined product with a potassium source solution evenly, performing a hydrothermal leaching at 100-160 °C, filtering after cooling, and drying the filtrate to obtain silicon-containing super-mineral-source potassium humate. The method of the present invention uses rice husks, a biomass agricultural and forestry solid waste with a relatively high silicon content, and a low-cost potassium salt as raw materials to prepare a high-value-added potassium humate water-soluble fertilizer, enabling the full and effective resource utilization and harmless recycling of rice husks, and having significant economic benefits and application prospects.

Description

Technical Field

[0001] The present invention belongs to the technical field of agricultural and forestry solid waste treatment and resource utilization, and specifically relates to a method and application for preparing silicon-containing super-mineral-source potassium humate from rice husks. Background Art

[0002] Humic acid is mainly a multifunctional material extracted and prepared from lignite, weathered coal, peat, etc. It has various functional groups, including quinones, hydroxyl groups, carbonyl groups, phenolic and alcoholic hydroxyl groups, and methoxy groups. In recent years, humic acid has been widely used in the fields of industry, agriculture, medicine and health, and environmental protection. In agriculture, humic acid-based fertilizers synthesized with elements such as nitrogen, phosphorus, and potassium have obvious effects of enhancing fertilizer efficiency, improving soil, stimulating crop growth, and improving the quality of agricultural products, and are suitable for modern agricultural production that advocates pollution-free agricultural production, green food, and pollution-free environmental protection fertilizers. Currently, most potassium humates on the market are mineral-source potassium humates, but there are certain defects in the extraction of mineral-source potassium humates: First, most humic acids on the market are made from coal, but the mineral-source raw materials such as weathered coal or lignite with a high humic acid content are very limited, the transportation cost is relatively high, and this non-renewable resource is decreasing day by day. Second, using coal to extract potassium humate will produce about half of the solid residue, and the yield of potassium humate is relatively low (only about 54%). Third, the water solubility of mineral-source potassium humate is poor, its application is limited, and its added value is low. Fourth, the raw material potassium hydroxide used to prepare potassium humate is relatively expensive compared with other potassium salts and alkaline compounds, about 5,000 yuan / ton, and the use cost is also relatively high. Therefore, developing suitable renewable resources, cheap potassium sources, and efficient preparation methods is of great significance for the further development of potassium humate.

[0003] Rice husks belong to a renewable resource with a huge output and wide sources. Rice husks contain a large amount of silicon elements and are known as the "representative of silicate plants". Silicon is not only an important component in the bodies of most crops (especially gramineous crops such as rice, wheat, corn, and sorghum), but also plays an important role in the growth and development process of crops. It is an essential nutrient element for the growth of many crops, especially having an obvious promoting effect on crops that need to supplement silicon. However, most rice husks are not effectively utilized at present. The common treatment methods for rice husks are generally direct stacking, landfill, or open burning, but the above treatment methods have great hazards: First, open stacking occupies a large amount of land resources; Second, landfill or burning will seriously damage the soil balance, aggravate soil compaction, cause serious air pollution, and endanger human health; Third, burning straw is extremely easy to ignite the surrounding area, resulting in large-area fires that are difficult to control and causing economic losses. To avoid the waste of a large amount of renewable resources and the silicon elements in rice husks, as well as the harm to the environment and human body, it is necessary to carry out full and effective new resource utilization of rice husks.

[0004] In the 1990s, some researchers used solid agricultural and forestry waste such as crop straws and livestock manures as raw materials to prepare biochemical humic acid products similar to coal humic acid by biochemical technologies and apply them to agricultural production, such as biological fermentation method, hydrothermal method, etc. However, during the implementation process, there are disadvantages such as difficult simulation of the bacterial strain environment, unstable product quality, low yield, high production cost, and unsuitability for large-scale production. Therefore, it is necessary to develop a method with lower cost, simpler operation, higher efficiency, and easier industrialization for preparing humic acid products.

[0005] In the previous application CN113277492B of the main inventor of this application, a method for preparing potassium humate and biochar from agricultural and forestry waste was disclosed. The yield of potassium humate was increased by catalytic oxidation with potassium ferrate and co-heating quenching with KOH. However, the treatment reagents potassium ferrate and KOH used have relatively high prices, resulting in high costs. In the previous application CN115611683A of the main inventor of this application, a method for preparing a water-soluble fertilizer containing super-mineral-source humic acid from agricultural and forestry biomass solid waste was disclosed. Starting from agricultural and forestry biomass solid waste, it is subjected to gradient roasting carbonization under the combined action of a catalyst (hydroxy iron oxide and / or iron oxide catalyst) and an activator (at least one of K3PO4, K2HPO4, KH2PO4, KNO3, KNO2, and K2CO3) to promote the recombination of organic matter carbon chains and obtain a weathered coal precursor. Then, under the action of an oxidant (at least one of KMnO4, H2O2, HNO3, CH3COOOH, and (NH4)2S2O8), its functional groups are enriched, and the organic matter is converted into super-mineral-source humic acid. The oxidation product is then added to an extraction agent solution (at least one of KOH, K2CO3, K4P2O7, and K2C2O4) for extraction to obtain a water-soluble fertilizer product containing super-mineral-source humic acid. However, this method has complex treatment steps and treatment reagents. It requires the combined action of a catalyst and a large amount of activator (10% - 50% of the mass of the biomass solid waste powder), and gradient roasting carbonization with controlled oxygen content, as well as further reaction with an oxidant to increase the organic matter conversion rate to 50% - 90%, and the super-mineral-source humic acid yield is about 52%. There is still room for further improvement in its organic matter conversion rate and super-mineral-source humic acid yield. Summary of the Invention

[0006] Aiming at the disadvantages and deficiencies of the above existing technologies, the primary object of the present invention is to provide a method for preparing silicon-containing super-mineral source potassium humate using rice husks. The method of the present invention uses rice husks, a biomass agricultural and forestry solid waste with a relatively high silicon content, and inexpensive potassium salts as raw materials, and adopts a method of roasting under the catalysis of a nano-metal oxide catalyst and stabilizer conditions, hydrothermal extraction reaction, and rapid cooling to prepare a high-value-added potassium humate water-soluble fertilizer, enabling the full and effective resource utilization and harmless recycling of rice husks, and achieving the efficient preparation of high-quality silicon-containing super-mineral source potassium humate water-soluble fertilizer at a relatively low cost. The conversion rate of organic matter in agricultural and forestry solid waste rice husks has been greatly improved, reaching 89% - 98%, and the yield of potassium humate has been effectively increased, reaching 79% - 89%.

[0007] Another object of the present invention is to provide a silicon-containing super-mineral source potassium humate prepared by the above method.

[0008] Another object of the present invention is to provide the application of the above silicon-containing super-mineral source potassium humate in promoting plant growth.

[0009] The object of the present invention is achieved by the following technical solutions:

[0010] A method for preparing silicon-containing super-mineral source potassium humate using rice husks, comprising the following preparation steps:

[0011] (1) Using a metal ion solution as a precursor, adding an alkali and a dispersant, and preparing a nano-metal oxide catalyst through a hydrothermal reaction;

[0012] (2) Mixing the pretreated rice husks with the nano-metal oxide catalyst and stabilizer prepared in step (1), and performing a roasting treatment at a temperature of 180 - 400 °C and under an air atmosphere condition to obtain a roasted product;

[0013] (3) Stirring and mixing the roasted product obtained in step (2) with a potassium source solution evenly, and then performing hydrothermal extraction at a temperature of 100 - 160 °C;

[0014] (4) Cooling the solution after hydrothermal extraction in step (3), filtering, and drying the filtrate to obtain silicon-containing super-mineral source potassium humate.

[0015] Further, in step (1), the metal ion solution is a copper sulfate solution, a copper nitrate solution, a ferric nitrate solution, a ferric chloride solution, etc., and the concentration of the metal ion solution is 0.1 - 0.4 mol / L.

[0016] Further, in step (1), the alkali is sodium hydroxide, and the addition amount of the alkali is 2 - 6 mol / L.

[0017] Further, the dispersant described in step (1) includes at least one of ethylene glycol, polyethylene glycol, and sodium dodecyl sulfonate, and the mass concentration of the added dispersant is 1% - 5%.

[0018] Further, the temperature of the hydrothermal reaction in step (1) is 130 - 180 °C, and the time is 12 - 24 h.

[0019] Further, the steps of the pretreatment in step (2) are washing and drying, pulverizing and sieving. The drying temperature is 70 - 80 °C, and the sieving is through a 100 - 200 mesh sieve.

[0020] Further, the dosage of the nano metal oxide catalyst in step (2) is 0.5% - 3% of the mass of the rice husk.

[0021] Further, the stabilizer in step (2) refers to at least one of fly ash, magnesium hydroxide, calcium carbonate, and tricalcium phosphate, and the dosage of the stabilizer is 2% - 10% of the mass of the rice husk.

[0022] Further preferably, the calcination treatment temperature in step (2) is 200 - 250 °C, and the time of the calcination treatment is 80 - 160 min.

[0023] Further, the potassium source solution in step (3) refers to potassium carbonate solution, potassium bicarbonate solution, potassium nitrate solution, potassium phosphate solution, etc.; the mass ratio of the added amount of the potassium source to the mass of the rice husk is (0.05 - 0.6):1.

[0024] Further, the cooling in step (4) means transferring to a rapid cooling kettle and rapidly cooling to 70 - 80 °C within 5 min.

[0025] Further, the drying in step (4) means drying at a temperature of 60 - 80 °C.

[0026] Further, the nano metal oxide catalyst is separated from the filter residue after filtration in step (4) by magnetic separation or flotation, and then recycled to step (2) for reuse. The remaining solid residue is dried and used as a soil conditioner.

[0027] A silicon-containing super-mineral source humic acid potassium is prepared by the above method.

[0028] Application of the above-mentioned silicon-containing super-mineral source humic acid potassium in promoting plant growth.

[0029] Further, the application process is as follows: The silicon-containing super-mineral source humic acid potassium is formulated into a water-soluble fertilizer with a concentration of 5 - 60 mg / L and sprayed during the plant growth process; the plants include crops such as corn, wheat, rice, and beans.

[0030] The principle of the present invention is as follows: By adding a dispersant during the preparation process of the metal oxide catalyst, the dispersion is further promoted, and agglomeration during the reaction process is prevented, which is beneficial to obtaining a nano-scale metal oxide catalyst. The rice husk is mixed evenly with the nano metal oxide catalyst and roasted. The nano metal oxide catalyst has strong oxidizing property and activity, and a large specific surface area, which can promote the full cracking and carbonization of organic matter in the rice husk and the conversion of silicon element into soluble silicon, promote the conversion of humic acid from macromolecules to small molecules, and at the same time promote the formation of humification precursors, which is beneficial to improving the yield of potassium humate. Adding a stabilizer (flame retardant) can make the prepared humic acid have better high-temperature resistance and thermal stability, reduce the volatilization of humic acid and reduce losses; it can also prevent excessive oxidation under air conditions, without the need to control the oxygen content in the atmosphere, so that more of the roasted products are converted into soluble humic acid substances, and the yield of potassium humate is increased. The addition of a cheap potassium source provides a source of potassium oxide in potassium humate. The hydrothermal extraction process causes the biomass to crack and recombine, promoting the formation of a large number of functional groups such as carboxyl, hydroxyl, carbonyl, quinone and methoxy groups in potassium humate. Rapid cooling can further increase the content of oxygen-containing functional groups, making potassium humate a potassium humate fertilizer with relatively high contents of oxygen, potassium and silicon elements, which has a good promoting effect on plant growth.

[0031] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0032] (1) The present invention uses rice husk as the main raw material for preparation. The rice husk mainly contains a large amount of lignin (21%-26%), cellulose (35.5%-45%), SiO2 (11.05%-19.80%), etc. Its source is wide, it is convenient for transportation, and the cost is low; at the same time, the silicon element in the rice husk enters the potassium humate, and a potassium humate fertilizer with excellent performance containing silicon element and good water solubility can be obtained, so that it is not restricted in subsequent applications.

[0033] (2) The present invention uses potassium carbonate, potassium bicarbonate, potassium nitrate or potassium phosphate, etc. as the potassium source to catalytically prepare silicon-containing super-mineral-source potassium humate, which is relatively cheap compared to the commonly used potassium hydroxide at present, can effectively reduce the production cost, and improves the economic benefit of the product; at the same time, it can increase the yield of potassium humate, enabling the full conversion of organic matter and the full utilization of rice husk.

[0034] (3) The oxygen, potassium contained in the catalyst and potassium source used in the present invention and the silicon element contained in the rice husk are fixed into the generated potassium humate water-soluble fertilizer. The prepared silicon-containing potassium humate water-soluble fertilizer has good water solubility, and its quality is better than that of mineral-source potassium humate, with a higher added value, which is beneficial to agricultural applications.

[0035] (4) The nano-metal oxide catalyst prepared by the present invention is relatively clean and environmentally friendly, can be recycled while effectively increasing the yield of potassium humate; and further adding an appropriate amount of stabilizers (such as fly ash, magnesium hydroxide, calcium carbonate, tricalcium phosphate, etc.) during the calcination process can improve the stability of humic acid, endowing it with better high-temperature and thermal stability, reducing the volatilization of humic acid and losses; it can also prevent excessive oxidation under air conditions, without the need to regulate the oxygen content in the atmosphere, enabling more of the calcination products to be converted into soluble humic acid substances, thereby increasing the yield of potassium humate. Ultimately, the conversion rate of organic matter in agricultural and forestry solid waste rice husks is greatly improved, reaching 89% - 98%, and the yield of potassium humate is effectively increased, up to 79% - 89%. A small amount of solid residue remaining after the extraction of potassium humate still contains some nutrients and organic matter, which can be used as a soil conditioner to improve soil quality, adjust soil pH, increase soil fertility and water retention capacity, etc., realizing the efficient utilization of rice husk resources and the sustainable development of the environment.

[0036] (5) The rapid cooling adopted in the present invention can effectively increase the content of various active functional groups such as carboxyl, hydroxyl, and phenolic groups in potassium humate, thereby improving the quality and performance of super-mineral-source potassium humate.

[0037] (6) The process of the present invention is simple, low-cost, and easy to industrialize, and can realize the resource utilization of agricultural and forestry solid waste rice husks, producing high-value-added potassium humate water-soluble fertilizers. Taking the growth of pea seeds as an example, the prepared silicon-containing potassium humate water-soluble fertilizer has an obvious promoting effect on pea growth. Description of the Drawings

[0038] Figure 1 It is a graph showing the yield of potassium humate synthesized in Examples 1 - 4 of the present invention and the rice husk conversion rate results.

[0039] Figure 2 It is a graph showing the water solubility test results of the silicon-containing super-mineral-source potassium humate prepared in Example 2 of the present invention.

[0040] Figure 3 It is an infrared spectrum diagram of the potassium humate synthesized in Example 2 of the present invention.

[0041] Figure 4 It is a nuclear magnetic carbon spectrum diagram of the potassium humate synthesized in Example 2 of the present invention.

[0042] Figure 5 It is a graph showing the plant growth experiment test results of the silicon-containing potassium humate water-soluble fertilizer obtained in Example 2 of the present invention.

[0043] Figure 6 It is a scanning electron microscope image of the nano-scale copper oxide (a) and iron oxide (b) catalysts prepared in Examples 1 and 2 of the present invention.

[0044] Figure 7 This is the experimental result diagram for the recycling of the catalyst in Example 2 of the present invention. Detailed implementation manners

[0045] The present invention will be further described in detail below in conjunction with examples and the accompanying drawings, but the implementation manners of the present invention are not limited thereto.

[0046] Example 1

[0047] (1) Using a 0.1 mol / L copper sulfate solution as a precursor, adding 2 mol / L sodium hydroxide and 1% ethylene glycol dispersant, and performing hydrothermal treatment at 130 °C for 12 h to prepare a nano-copper oxide catalyst.

[0048] (2) Taking 5 g of rice husks washed with deionized water, dried at 80 °C, and sieved through a 100-mesh sieve, adding 0.5% (by mass of rice husks) of the catalyst and 5% (by mass of rice husks) of magnesium hydroxide, and calcining in an air atmosphere at 180 °C for 80 min to obtain a calcined product.

[0049] (3) Adding the calcined product and potassium carbonate solution to a reaction kettle at a mass ratio of 0.1:1 (potassium carbonate: rice husks), and performing hydrothermal leaching reaction at 100 °C for 100 min.

[0050] (4) Transferring the product after the reaction in step (3) to a rapid cooling kettle and rapidly cooling it to 70 - 80 °C within 5 min, washing and filtering until the filtrate is almost colorless to obtain a filtrate and a filter residue. The obtained filtrate is dried at 60 °C to obtain silicon-containing super-mineral source potassium humate. The nano-copper oxide catalyst is separated from the filter residue by flotation and then reused in step (2) for recycling. The remaining solid residue can be used as a soil conditioner after drying.

[0051] In this example, 5 g of agricultural and forestry solid waste rice husks are treated to obtain 4.25 g of a solid product of silicon-containing super-mineral source potassium humate fertilizer. The obtained potassium humate meets the requirements of GB / T 33804-2017 potassium humate for agricultural use and is a first-class product; the unreacted residue is 0.385 g (the dry weight of the residue remaining after removing the magnesium hydroxide stabilizer and copper oxide catalyst from the filter residue obtained in step (4)). The yield of potassium humate can reach 85%, the conversion rate of rice husks is as high as 92.3%, and the catalyst can be effectively recycled 4 times. (Note: The yield of potassium humate = the solid product of silicon-containing super-mineral source potassium humate fertilizer / the amount of rice husks used; the conversion rate of rice husks = 1 - the unreacted residue / the amount of rice husks used; the effective recycling of the catalyst means that the yield of potassium humate obtained by cyclic catalytic conversion > 75%).

[0052] To further prove the effects of the catalyst and stabilizer of the present invention on the yield of potassium humate and the conversion rate of rice husk, control groups without adding nano-copper oxide catalyst and without adding magnesium hydroxide stabilizer were respectively set up, and silicon-containing super-mineral source potassium humate was prepared under the same other conditions. The results showed that the yield of potassium humate without adding nano-copper oxide catalyst was 72.5%, and the conversion rate of rice husk was 85.2%; the yield of potassium humate without adding magnesium hydroxide stabilizer was 80.2%, and the conversion rate of rice husk was 84.6%.

[0053] Example 2

[0054] (1) Using 0.2 mol / L ferric chloride solution as the precursor, adding 3 mol / L sodium hydroxide and 2% polyethylene glycol dispersant, and hydrothermally reacting at 150 °C for 18 h to prepare a nano-iron oxide catalyst.

[0055] (2) Take 5 g of rice husk washed with deionized water, dried at 80 °C, and sieved through a 100-mesh sieve, add 1% (by mass of rice husk) of the catalyst and 10% (by mass of rice husk) of fly ash, and calcine at 230 °C for 110 min to obtain a calcined product.

[0056] (3) Add the calcined product and potassium bicarbonate solution to the reaction kettle at a mass ratio of 0.2:1 (potassium bicarbonate: rice husk), and carry out hydrothermal leaching reaction at 120 °C for 120 min.

[0057] (4) After the reaction in step (3) is completed, transfer the product to a rapid cooling kettle and rapidly cool it to 70 - 80 °C within 5 min, wash and filter until the filtrate is almost colorless to obtain a filtrate and a filter residue. Dry the obtained filtrate at 60 °C to obtain silicon-containing super-mineral source potassium humate. Magnetically separate the nano-iron oxide catalyst from the filter residue, and then recycle it back to step (2) for recycling. The remaining solid residue can be used as a soil conditioner after drying.

[0058] In this example, 5 g of agricultural and forestry solid waste rice husk was treated to obtain 4.40 g of solid product of silicon-containing super-mineral source potassium humate fertilizer. The obtained potassium humate meets the requirements of GB / T33804-2017 potassium humate for agricultural use and is a first-class product; the unreacted residue is 0.2 g (the dry weight of the residue remaining after removing fly ash stabilizer and iron oxide catalyst from the filter residue obtained in step (4)). The yield of potassium humate can reach 88%, and the conversion rate of rice husk is as high as 96%. The catalyst can be effectively recycled 5 times. (Note: The yield of potassium humate = the solid product of silicon-containing super-mineral source potassium humate fertilizer / the amount of rice husk used; the conversion rate of rice husk = 1 - the unreacted residue / the amount of rice husk used; the effective recycling of the catalyst means that the yield of potassium humate obtained by cyclic catalytic conversion > 75%).

[0059] To further prove the effects of the catalyst and stabilizer of the present invention on the yield of potassium humate and the conversion rate of rice husk, control groups without adding nano-iron oxide catalyst and without adding fly ash stabilizer were respectively set up, and silicon-containing super-mineral source potassium humate was prepared under the same other conditions. The results showed that the yield of potassium humate without adding nano-iron oxide catalyst was 73.8%, and the conversion rate of rice husk was 84.7%; the yield of potassium humate without adding fly ash stabilizer was 80.8%, and the conversion rate of rice husk was 85.4%.

[0060] Example 3

[0061] (1) Using 0.2 mol / L ferric nitrate solution as the precursor, adding 4 mol / L sodium hydroxide and 2% sodium dodecyl sulfonate dispersant, and hydrothermal reacting at 150 °C for 20 h to prepare the nano-iron oxide catalyst.

[0062] (2) Take 5 g of rice husk washed with deionized water, dried at 80 °C, and sieved through a 100-mesh sieve, add 2% (by mass of rice husk) of the catalyst and 10% (by mass of rice husk) of calcium carbonate, and calcine at 280 °C for 140 min to obtain the calcined product.

[0063] (3) Add the calcined product and potassium nitrate solution to the reaction kettle at a mass ratio of 0.4:1 (potassium nitrate: rice husk), and carry out hydrothermal leaching reaction at 140 °C for 140 min.

[0064] (4) After the reaction in step (3) is completed, transfer the product into a rapid cooling kettle and rapidly cool it to 70 - 80 °C within 5 min, wash and filter until the filtrate is almost colorless to obtain the filtrate and filter residue. Dry the obtained filtrate at 60 °C to obtain silicon-containing super-mineral source potassium humate. Magnetically separate the nano-iron oxide catalyst from the filter residue, and then recycle it back to step (2) for recycling. The remaining solid residue can be used as a soil conditioner after drying.

[0065] In this example, 5 g of agricultural and forestry solid waste rice husk was treated to obtain 4.05 g of solid product of silicon-containing super-mineral source potassium humate fertilizer. The obtained potassium humate meets the requirements of GB / T33804-2017 potassium humate for agricultural use and is of first-class quality; the unreacted residue is 0.47 g (the dry weight of the residue remaining after removing the calcium carbonate stabilizer and iron oxide catalyst from the filter residue obtained in step (4)). The yield of potassium humate can reach 81%, and the conversion rate of rice husk is as high as 90.6%. The catalyst can be effectively recycled 3 times. (Note: The yield of potassium humate = solid product of silicon-containing super-mineral source potassium humate fertilizer / rice husk dosage; the conversion rate of rice husk = 1 - unreacted residue / rice husk dosage; the effective recycling of the catalyst means that the yield of potassium humate in the catalytic conversion cycle > 75%).

[0066] To further prove the effects of the catalyst and stabilizer of the present invention on the yield of potassium humate and the conversion rate of rice husk, control groups without adding nano-iron oxide catalyst and without adding calcium carbonate stabilizer were respectively set up, and silicon-containing super-mineral-source potassium humate was prepared under the same other conditions. The results showed that the yield of potassium humate without adding nano-iron oxide catalyst was 71.6%, and the conversion rate of rice husk was 82.2%; the yield of potassium humate without adding calcium carbonate stabilizer was 76.1%, and the conversion rate of rice husk was 81.5%.

[0067] Example 4

[0068] (1) Using 0.4 mol / L copper nitrate solution as the precursor, adding 5 mol / L sodium hydroxide and 3% polyethylene glycol dispersant, hydrothermal reaction was carried out at 170 °C for 20 h to prepare nano-copper oxide catalyst.

[0069] (2) Take 5 g of rice husk washed with deionized water, dried at 80 °C, and sieved through a 100-mesh sieve, add 2.5% (by mass of rice husk) of the catalyst and 5% (by mass of rice husk) of tricalcium phosphate, and calcine at 320 °C for 160 min to obtain a calcined product.

[0070] (3) Add the calcined product and potassium phosphate solution to the reaction kettle according to a mass ratio of 0.4:1 (potassium phosphate: rice husk), and carry out hydrothermal leaching reaction at 160 °C for 160 min.

[0071] (4) After the reaction in step (3) is completed, transfer the product to a rapid cooling kettle and rapidly cool it to 70 - 80 °C within 5 min, wash and filter until the filtrate is almost colorless to obtain a filtrate and a filter residue. Dry the obtained filtrate at 60 °C to obtain silicon-containing super-mineral-source potassium humate. Separate the nano-copper oxide catalyst from the filter residue by flotation, and then recycle it back to step (2) for recycling. The remaining solid residue can be used as a soil conditioner after drying.

[0072] In this example, 5 g of agricultural and forestry solid waste rice husk was treated to obtain 3.98 g of solid product of silicon-containing super-mineral-source potassium humate fertilizer. The obtained potassium humate meets the requirements of GB / T33804-2017 potassium humate for agricultural use and is a first-class product; the unreacted residue is 0.55 g (the dry weight of the residue remaining after removing the tricalcium phosphate stabilizer and copper oxide catalyst from the filter residue obtained in step (4)). The yield of potassium humate can reach 79.6%, and the conversion rate of rice husk is as high as 89%. The catalyst can be effectively recycled 3 times. (Note: The yield of potassium humate = the solid product of silicon-containing super-mineral-source potassium humate fertilizer / the amount of rice husk used; the conversion rate of rice husk = 1 - the unreacted residue / the amount of rice husk used; the effective recycling of the catalyst means that the yield of potassium humate obtained by cyclic catalytic conversion > 75%).

[0073] To further prove the effects of the catalyst and stabilizer of the present invention on the yield of potassium humate and the conversion rate of rice husk, control groups without adding nano-copper oxide catalyst and without adding tricalcium phosphate stabilizer were respectively set up, and silicon-containing super-mineral source potassium humate was prepared under the same other conditions. The results showed that the yield of potassium humate without adding nano-copper oxide catalyst was 68.4%, and the conversion rate of rice husk was 79.7%; the yield of potassium humate without adding tricalcium phosphate stabilizer was 73.8%, and the conversion rate of rice husk was 80.2%.

[0074] The yield and rice husk conversion rate diagrams of the synthesized potassium humate in Examples 1 to 4 above are as Figure 1 shown. From the above results, it can be seen that the potassium humate obtained in Example 2 had the highest yield and the highest rice husk conversion rate.

[0075] The water solubility test result diagram of the silicon-containing super-mineral source potassium humate prepared in Example 2 above is as Figure 2 shown. The left figure is the state when potassium humate was just added to water, and the right figure is the dissolution state after 30 s. From the Figure 2 results, it can be seen that potassium humate was completely dissolved, indicating that the silicon-containing super-mineral source potassium humate prepared by the present invention had good water solubility.

[0076] The infrared spectrum diagram and nuclear magnetic carbon spectrum diagram of the silicon-containing super-mineral source potassium humate prepared in Example 2 above are respectively as Figure 3 and Figure 4 shown. It can be seen that the target product potassium humate was obtained.

[0077] Taking the preparation of water-soluble fertilizer by spraying pea seeds with the silicon-containing super-mineral source potassium humate obtained in Example 2 as an example for plant growth research, the potassium humate was added to water to prepare a potassium humate solution with a concentration of 20 mg / L, and the pea seeds were sprayed at regular intervals. The upper and root lengths of the pea seedlings were measured by the ruler measurement method, and the fresh weight and dry weight changes during the growth of peas were analyzed by the gravimetric method, and a commercial mineral source potassium humate was used for comparison. The results are as Figure 5 shown. From the Figure 5 results, it can be seen that the water-soluble fertilizer of the silicon-containing super-mineral source potassium humate prepared by the present invention had good ability to promote plant growth, and its promoting effect on plant growth was better than that of the commercially available commercial mineral source potassium humate.

[0078] The scanning electron microscope diagrams of the nano-copper oxide (a) and nano-iron oxide (b) catalysts prepared in Examples 1 and 2 above are as Figure 6 shown. It can be seen that the prepared nano-copper oxide and nano-iron oxide reached the nano-level standard.

[0079] The experimental results of recycling the catalyst in the solid residue obtained in Example 2 above are as Figure 7 shown. It can be seen that the present invention can realize the recycling of the catalyst, realize the high-value utilization of rice husk, and is relatively friendly to the environment.

[0080] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited by the above embodiments. Any other changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement methods and are all included within the protection scope of the present invention.

Claims

1. A method for preparing silicon-containing super-mineral source potassium humate using rice husks, characterized in that, It includes the following preparation steps: (1) Using a metal ion solution as a precursor, adding an alkali and a dispersant, and preparing a nano metal oxide catalyst through a hydrothermal reaction; (2) Mixing the pretreated rice husk with the nano metal oxide catalyst and stabilizer prepared in step (1), and performing a calcination treatment at a temperature of 180-400 °C and in an air atmosphere to obtain a calcined product; (3) Stirring and mixing the calcined product obtained in step (2) with a potassium source solution evenly, and then performing hydrothermal leaching at a temperature of 100-160 °C; (4) Cooling the solution after hydrothermal leaching in step (3), filtering, and drying the filtrate to obtain silicon-containing super-mineral source potassium humate; In step (1), the metal ion solution is a copper sulfate solution, a copper nitrate solution, an iron nitrate solution, or an iron chloride solution, and the concentration of the metal ion solution is 0.1-0.4 mol / L; the alkali is sodium hydroxide, and the addition amount of the alkali is 2-6 mol / L; the dispersant includes at least one of ethylene glycol, polyethylene glycol, and sodium dodecyl sulfonate, and the mass concentration of the added dispersant is 1%-5%; In step (2), the dosage of the nano metal oxide catalyst is 0.5%-3% of the mass of the rice husk; the stabilizer refers to at least one of fly ash, magnesium hydroxide, calcium carbonate, and tricalcium phosphate, and the dosage of the stabilizer is 2%-10% of the mass of the rice husk; the calcination treatment temperature is 200-250 °C, and the calcination treatment time is 80-160 min; In step (3), the potassium source solution refers to a potassium carbonate solution, a potassium bicarbonate solution, a potassium nitrate solution, or a potassium phosphate solution; the mass ratio of the added amount of the potassium source to the mass of the rice husk is (0.05-0.6):1; In step (4), the cooling refers to transferring it into a rapid cooling kettle and rapidly cooling to 70-80 °C within 5 min; the drying refers to drying at a temperature of 60-80 °C.

2. The method for preparing silicon-containing super-mineral source potassium humate using rice husks according to claim 1, characterized in that, In step (1), the temperature of the hydrothermal reaction is 130-180 °C, and the time is 12-24 h.

3. A method for preparing silicon-containing super-mineral source potassium humate using rice husks according to claim 1, characterized in that, In step (2), the steps of the pretreatment are washing, drying, pulverizing, and sieving. The drying temperature is 70-80 °C, and the sieving is through a 100-200 mesh sieve.

4. A method for preparing silicon-containing super-mineral source humic acid potassium using rice husks according to claim 1, characterized in that, In step (4), the nano metal oxide catalyst is separated from the filter residue after filtration by magnetic separation or flotation, and then recycled to step (2) for recycling. The remaining solid residue is dried and used as a soil conditioner.

5. A silicon-containing super-mineral-source potassium humate, characterized in that, Prepared by the method according to any one of claims 1 to 4.

6. Use of a silicon-containing super-mineral source potassium humate as described in claim 5 in the process of promoting plant growth, characterized in that, The application process is as follows: preparing the silicon-containing super-mineral source potassium humate into a water-soluble fertilizer with a concentration of 5-60 mg / L and spraying it during the plant growth process; the plants include corn, wheat, rice, or leguminous crops.

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