Coal gangue-based slow-release silicon fertilizer and preparation method thereof

Abstract

The application provides a slow-release silicon fertilizer prepared from coal gangue and a preparation method thereof, and comprises the following steps: a) crushing the coal gangue and performing superfine ball milling to obtain superfine coal gangue powder; b) feeding the superfine coal gangue powder into a multi-stage suspension calcination reactor to perform one-stage calcination: calcining at 450-550 DEG C and spraying a potassium nitrate solution in this stage; c) two-stage calcination: spraying a concentrated potassium carbonate solution in this stage, the spraying mode is a high-pressure atomizing nozzle, the droplet size is 10-50 mu m, and the spraying speed is 0.02-0.5 L / min; d) sorting out a component rich in amorphous silicon oxide; and e) mixing the component rich in amorphous silicon oxide with limestone at a mass ratio of 4:6-8, and processing to obtain a coal gangue-based slow-release silicon fertilizer. The application has the advantages of being capable of accurately controlling the calcination process, preventing overburning and sintering, synchronously introducing nutrient elements, having stable components, and being good in slow-release effect.

Description

Technical Field

[0001] This invention relates to the field of coal gangue resource recycling technology, specifically to a slow-release silicon fertilizer prepared from coal gangue and its preparation method. Background Technology

[0002] Coal gangue is a solid waste generated during coal mining and washing. Its main components are silicon dioxide and aluminum oxide, along with small amounts of iron oxide, calcium oxide, carbon, and various trace elements. Large stockpiles of coal gangue not only occupy land but also cause environmental pollution. Activating coal gangue through calcination to produce agricultural silicon fertilizer is an effective way to achieve high-value resource utilization. Silicon fertilizer can improve soil structure, promote crop growth, and enhance stress resistance. Field trials have shown that applying coal gangue silicon fertilizer can increase crop yields and improve crop quality. Crops treated with silicon fertilizer exhibit stronger drought, flood, and pest resistance, reducing pesticide use and aligning with the development direction of green agriculture. Long-term application can increase soil cation exchange capacity, promote aggregate formation, and alleviate soil compaction.

[0003] Silicon and aluminum in coal gangue mainly exist in the form of silicate minerals such as kaolinite (Al2Si2O2(OH)4) and illite. These minerals have stable crystal structures, are poorly soluble in water, and cannot be directly absorbed by plants. High-temperature calcination is necessary to break down their crystal structure and transform them into soluble amorphous active SiO2 and Al2O3. However, in traditional fixed-bed or rotary kiln calcination processes, due to low heat transfer efficiency and uneven heating of the material, "over-burning" or "sintering" is highly likely to occur. "Over-burning" refers to excessively high calcination temperatures or prolonged calcination times, leading to vitrification of the material particle surface, pore closure, and a reduction in active sites. During sintering, coal gangue particles agglomerate to form dense lumps, not only causing a surge in energy consumption for subsequent crushing but also encapsulating effective components, blocking the pore structure, and causing them to lose the specific surface area and pore volume required for fertilizer application, resulting in poor water and fertilizer retention capacity. Existing technologies involve separately crushing coal gangue and organic solid waste to obtain coal gangue powder and organic solid waste powder; mixing the coal gangue powder and organic solid waste powder to obtain a mixture; subjecting the mixture to pyrolysis, calcination, and stabilization to obtain activated material; and then quenching and pulverizing the activated material to obtain the silicon fertilizer. However, due to the difficulty in controlling the composition of organic solid waste, the quality of the finished product is unstable, the effective silicon content fluctuates greatly, and it is impossible to achieve effective compounding of multiple elements such as potassium (K). Furthermore, the low porosity of silicon particles affects the slow-release effect and fertility. Existing multi-effect citrate-soluble silicon fertilizers consist of silicon-containing waste residue and an activator. The silicon activator is a mixture of potassium carbonate and calcium carbonate, containing various nutrients such as silicon, potassium, and calcium, which has a good effect on improving soil fertility, improving the soil environment of polluted farmland, and promoting crop yield. However, the actual effective silicon content is low, affecting the utilization rate of Si and K and the slow-release effect.

[0004] Therefore, existing technologies suffer from problems such as poor slow-release effect of silicon fertilizer, single chemical elements, unstable product composition, especially effective silicon content, and difficulty in controlling product quality. Developing a new technology for preparing silicon fertilizer from coal gangue that can precisely control the calcination process, prevent over-burning and sintering, and simultaneously introduce nutrient elements, with stable composition and good slow-release effect, is of great significance for realizing the high-value-added resource utilization of coal gangue and developing green agriculture. Summary of the Invention

[0005] To overcome the shortcomings of existing technologies, this application provides a coal gangue-based slow-release silicon fertilizer and its preparation method, which has the advantages of being able to precisely control the calcination process, prevent over-burning and sintering, introduce nutrients simultaneously, have stable composition, and have good slow-release effect.

[0006] The embodiments of this application are implemented as follows:

[0007] In a first aspect, this application provides a method for preparing a coal gangue-based slow-release silicon fertilizer, comprising the following steps:

[0008] a) The coal gangue is crushed and subjected to ultrafine ball milling to obtain ultrafine coal gangue powder with a particle size D50 of 5-15μm;

[0009] b) The ultrafine coal gangue powder is fed into a multi-stage suspension calcination reactor for a first stage of calcination: calcination is carried out at 450-550℃ for 20-30 minutes, and a potassium nitrate solution with a concentration of 5-15 wt% is sprayed during this stage, with the mass ratio of potassium nitrate solution to coal gangue powder being 1:200-1:1000.

[0010] c) The material after the first stage of calcination is subjected to a second stage of calcination in the multi-stage suspension calcination reactor: the temperature is raised to 900-950℃ and calcined for 10-15 minutes. During this stage, a potassium carbonate solution with a concentration of 8-20 wt% is sprayed. The mass ratio of potassium carbonate solution to coal gangue powder is 1:500-1:600. The potassium carbonate solution is sprayed using a high-pressure atomizing nozzle with a droplet size of 10-50 μm and a spraying speed of 0.02-0.5 L / min.

[0011] d) Collect the calcination products and separate out the components rich in amorphous silica;

[0012] e) The component rich in amorphous silica is mixed with limestone at a mass ratio of 4:6-8, and then processed to obtain coal gangue-based slow-release silicon fertilizer.

[0013] Optionally, in step a), the ultrafine ball milling adopts a planetary ball mill with a ball-to-material ratio of 10:1-20:1, a rotation speed of 250-400 rpm, and a milling time of 2-4 hours.

[0014] Optionally, in step b), the calcination temperature is 470-490℃, the concentration of the potassium nitrate solution is 11-13wt%, and the mass ratio of potassium nitrate solution to coal gangue powder is 1:650-1:770.

[0015] Optionally, in step c), the temperature of the second-stage calcination is 910-933℃, the concentration of the potassium carbonate solution is 15-17wt%, and the mass ratio of the potassium carbonate solution to the coal gangue powder is 1:550-1:580.

[0016] Optionally, in step c), the gas introduced into the suspension calcination reactor during the second-stage calcination contains 2-10% by volume carbon dioxide.

[0017] Optionally, in step b), the potassium nitrate solution is sprayed using a high-pressure atomizing nozzle with droplets larger than 100 μm and a spraying speed of 0.1-0.3 L / min.

[0018] Optionally, in step c), the potassium carbonate solution is preheated to 60-80°C before spraying.

[0019] Optionally, in step d), dry air sorting is used with a wind speed of 8~12 m / s.

[0020] In a first aspect, this application provides an example of a coal gangue-based slow-release silicon fertilizer prepared by the aforementioned method, wherein the coal gangue-based slow-release silicon fertilizer has a citric acid-soluble silicon content greater than 27% and a specific surface area greater than 30 m². 2 / g.

[0021] Preferably, the coal gangue-based slow-release silicon fertilizer contains potassium (K) and calcium (Ca), has a citric acid-soluble silicon content greater than 34%, and a specific surface area greater than 36 m². 2 / g.

[0022] Beneficial effects include:

[0023] (1) Multi-stage suspension calcination and gradient temperature control: Suspension calcination allows for full and rapid heat exchange between ultrafine materials and hot air, avoiding local overheating. The first stage temperature of 450-550℃ aims to decompose the kaolinite structure and some organic matter in coal gangue. This stage uses a low temperature to balance activation efficiency while avoiding initial sintering of ultrafine materials. The temperature is then raised to a higher temperature (900-950℃) to complete the complete activation of the silicon structure. The gradient temperature method thermodynamically inhibits the occurrence of over-burning crystallization. In particular, for ultrafine materials, a lower temperature is used, increasing the difference between high and low temperature ranges, which is conducive to the full, rapid and uniform reaction of ultrafine materials, avoiding over-burning crystallization of ultrafine materials, as well as problems such as aggregation and growth of ultrafine materials and large particle size fluctuations during the calcination and activation process. This is beneficial for the formation of silicon fertilizer with rich pores after calcination and other treatments with limestone, which reacts fully with limestone and has an increased effective silicon content.

[0024] (2) Pore-expanding and oxidation effects of potassium nitrate: KNO3 solution is sprayed in a temperature range of 450-550℃. KNO3 decomposes rapidly at this temperature: 2KNO3→2KNO2+O2↑, and further decomposes into 2KNO3→K2O+NO↑+NO2↑ (or O2↑). Taking advantage of the low decomposition temperature of KNO3, the generated gases such as O2, NO, and NO2 are "explosively" released inside the coal gangue particles. This effectively complements the low-temperature calcination process, which opens up and expands the micropores of the particles, creating a rich mesoporous and macroporous structure. This effectively increases the specific surface area of ​​the finished product, as well as its high-temperature activation and reactivity, which is conducive to the reaction with components such as K and calcium oxide. This increases the content of water-soluble active silicon and the content of water-soluble usable K-containing silicon fertilizers such as potassium silicate (in existing technologies, potassium carbonate is generally added, but the actual amount of potassium available for plant use in the silicon fertilizer is low, resulting in high costs and even causing residual potassium carbonate and other alkaline substances in the silicon fertilizer, increasing the risk of soil alkalization and causing alkali damage). At the same time, the interaction between the oxygen and nitrogen oxides in the new ecosystem and the residual carbon and organic matter in the coal gangue makes carbon oxidation exothermic and increases reactivity, gasification increases porosity, and nitrogen is retained in the silicon fertilizer. The available nitrogen components provide a "cleaner" silicon-aluminum matrix for the subsequent high-temperature stage (i.e., further reduction of non-usable components), avoiding incomplete reactions and impurity encapsulation caused by carbon, and facilitating the introduction and improvement of the conversion ratio to form the nutrient element potassium.

[0025] (3) Potassium carbonate’s role in preventing sintering and further introducing nutrients: When the temperature in the second stage reaches above 900℃, K2CO3 solution is sprayed in. The molten potassium salt covers the surface of the coal gangue particles, which can effectively prevent direct contact between particles, like a “separation film”. This fundamentally prevents the sintering and bonding of ultrafine powder at high temperature, effectively realizes the calcination of ultrafine powder, avoids problems such as increased particle size and uneven distribution of ultrafine powder during high-temperature sintering, and facilitates the introduction and improvement of the conversion ratio of nutrients such as K and N.

[0026] (4) Potassium carbonate is sprayed using a high-pressure atomizing nozzle with droplet size of 10-50 μm. This size is close to the particle size of the ultrafine powder, which is conducive to achieving uniform dispersion. The droplets evaporate quickly, which is beneficial for the interaction between potassium carbonate and ultrafine powder particles, improving their effectiveness in preventing direct contact between particles. This helps prevent the sintering and agglomeration of ultrafine powder at high temperatures (possibly because the melting point of potassium carbonate is much higher than that of potassium nitrate; the small droplets evaporate quickly, and the potassium carbonate is evenly dispersed on the surface of the ultrafine powder, partially decomposing and partially melting at high temperatures. The molten potassium carbonate remains on the surface of the ultrafine powder, which helps reduce particle adhesion and growth). Controlling the droplet size is beneficial for coordinating with the calcination of ultrafine powder, avoiding problems such as increased particle size and uneven distribution during high-temperature sintering, and also helps to introduce and improve the conversion ratio of nutrients such as K and N. If the droplet size is too large (>50 μm): evaporation is slow, the ultrafine powder tends to increase in size, and reactivity decreases. Droplet size too small (<10μm): May be carried away by the airflow, reducing utilization rate, failing to effectively prevent direct contact between particles, and the ultrafine powder tends to increase in size. Spraying speed 0.02~0.5 L / min. Too fast a spraying speed: Droplets do not evaporate completely, leading to localized cooling, affecting melting and inhibiting adhesion, and the ultrafine powder tends to increase in size. Too slow a spraying speed: Insufficient droplet mixing power, affecting uniform mixing with the ultrafine powder, and the ultrafine powder tends to increase in size.

[0027] This invention, through the combined effects of physical ultrafine grinding and activation, multi-stage suspension calcination with multiple steps and temperatures, and the injection of chemical additives to reduce the risk of particle enlargement, improves activation conditions. This not only solves the core problems of deactivation and sintering but also constructs a multi-level porous structure, significantly increasing the product's specific surface area and pore volume, giving it excellent water and fertilizer retention and slow-release properties. Added nutrients such as potassium (K) are efficiently converted into usable potassium silicate and other components, directly integrated into the product, improving the utilization of silicon and potassium, enhancing fertilizer efficiency, and avoiding the increase of harmful component residues. Furthermore, by mixing with limestone, the composite effect with limestone is further enhanced, further regulating the slow-release rate of silicon fertilizer and achieving long-lasting fertilization. Detailed Implementation

[0028] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] It will be understood by those skilled in the art that, unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. It should also be understood that terms such as those defined in general dictionaries should be understood to have the meaning consistent with their meaning in the context of the prior art, and should not be interpreted in an idealized or overly formal sense unless specifically defined as herein. The reagents used herein may be commercially available related products, and performance testing standards refer to industry or national standards.

[0030] Those skilled in the art will understand that, unless specifically stated otherwise, the singular forms “a,” “an,” “the,” and “the” used herein may also include the plural forms. It should be further understood that the term “comprising” as used in this specification means the presence of the stated features, integers, steps, operations, elements, and / or components, but does not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. The term “and / or” as used herein includes all or any units and all combinations of one or more associated listed items.

[0031] To address the problems of poor slow-release effect, limited chemical elements, unstable product composition, especially the effective silicon content, and difficulty in consistently controlling product quality in existing silicon fertilizer technologies, this invention provides a coal gangue-based slow-release silicon fertilizer and its preparation method.

[0032] For example, a method for preparing a coal gangue-based slow-release silicon fertilizer is provided, comprising the following steps:

[0033] a) The coal gangue is crushed and subjected to ultrafine ball milling to obtain ultrafine coal gangue powder with a particle size D50 of 5-15μm (preferably 13-15μm, and can be 5μm, 6μm, 7μm, 8μm, 9μm, 11μm, 12μm, 13μm, 15μm, etc.). Through ultrafine ball milling of coal gangue, part of the ball milling energy is converted into the internal energy of the material, resulting in defects such as lattice distortion, dislocation, and amorphization. The diffusion path inside the particles becomes shorter, and atoms and ions migrate more easily, which is conducive to low-temperature activation and significantly improves the conversion rate and dissolution rate of effective silicon.

[0034] The ultrafine ball mill employs a planetary ball mill with a ball-to-powder ratio of 10:1-20:1 (selectable from 10:1, 11:1, 12:1, 13:1, 14:1, 15:1, 16:1, 17:1, 18:1, 20:1, etc.), a rotational speed of 250-400 rpm (preferably 330-360 rpm, 355-360 rpm, etc.), and a milling time of 2-4 hours. By using a high ball-to-powder ratio and high rotational speed, sufficient energy input and collision frequency are provided, increasing the likelihood of lattice distortion, dislocation formation, and amorphization defects, thus achieving physical activation. The high rotational speed allows the grinding media to operate in a highly efficient scattering impact mode, avoiding problems such as powder agglomeration caused by low speeds, which can lead to uneven particle size distribution.

[0035] b) The ultrafine coal gangue powder is fed into a multi-stage suspension calcination reactor for a first stage of calcination: calcination is carried out at 450-550℃ (preferably 457-496℃, 467-483℃, etc.) for 20-30 minutes (preferably 21-26 minutes, etc.). The first stage of low temperature is intended to decompose the kaolinite structure and some organic matter in the coal gangue. At this stage, the low temperature is used to balance activation efficiency and avoid the initial sintering of micron-sized particles of ultrafine materials (the kaolinite structure and some organic matter in the coal gangue, especially the presence of some organic matter, tend to increase the particle size when heated and decomposed, especially due to possible reasons such as rapid heating at high temperature and adhesion, which may lead to particle size increase). By using ultrafine ball milling on coal gangue, part of the ball milling energy is converted into the internal energy of the material during the milling process, which leads to defects such as lattice distortion, dislocation, and amorphization. The diffusion path inside the particles becomes shorter, and atoms and ions migrate more easily. Utilizing the characteristics of the ultrafine particles mentioned above, a better pre-activation effect can be achieved while maintaining efficiency at low temperature. At this time, a shorter calcination time can be used, which improves efficiency.

[0036] During this stage, a potassium nitrate solution with a concentration of 5-15 wt% (preferably 6-14 wt%, 7-11 wt%, etc.) is sprayed. The mass ratio of potassium nitrate solution to coal gangue powder is 1:200-1:1000 (preferably 1:330-1:860, 1:460-1:790, 1:580-1:780, etc.). The pore-expanding and oxidation effects of potassium nitrate are as follows: KNO3 solution is sprayed within a temperature range of 450-550℃. At this temperature, KNO3 rapidly decomposes: 2KNO3 → 2KNO2 + O2↑, and further decomposes into 2KNO3 → K2O + NO↑ + NO2↑ (or O2↑). Taking advantage of the low decomposition temperature of KNO3, the generated gases such as O2, NO, and NO2 "explode" out inside the coal gangue particles. This effectively complements the low-temperature calcination process, which opens up and expands the micropores of the particles. This facilitates the rapid removal of unusable carbon and organic matter, creating a rich mesoporous and macroporous structure. This effectively increases the specific surface area of ​​the finished product, as well as its high-temperature activation and reactivity. It also facilitates the reaction with components such as K and calcium oxide, increasing the content of water-soluble active silicon and the content of water-soluble usable K-containing silicon fertilizers such as potassium silicate (in existing technologies, potassium carbonate is generally added, but the actual amount of potassium available for plant use in the silicon fertilizer produced is relatively low, resulting in high costs and even causing residual alkaline substances such as potassium carbonate in the silicon fertilizer, increasing the risk of soil alkalization and causing alkali damage). At the same time, the interaction between the oxygen and nitrogen oxides in the new ecosystem and the residual carbon and organic matter in the coal gangue makes carbon oxidation exothermic and increases reactivity, gasification increases porosity, and nitrogen is retained in the silicon fertilizer. The available nitrogen components provide a "cleaner" silicon-aluminum matrix for the subsequent high-temperature stage (i.e., further reduction of non-usable components), avoiding incomplete reactions and impurity encapsulation caused by carbon, and facilitating the introduction and improvement of the conversion ratio to form the nutrient element potassium. Using a relatively low proportion of potassium nitrate solution, while maintaining a relatively high potassium nitrate content, effectively saves costs. It achieves activation while reducing the amount of additives used. It also mitigates issues such as agglomeration of ultrafine powders due to their high surface energy and strong sintering driving force. Excessive water content and localized over-wetting can lead to uneven drying, localized temperature drops, and even agglomeration. The relatively low proportion of ultrafine powder ensures proper matching of moisture evaporation and temperature under low-temperature conditions. During preheating and the initial calcination stage, the thin layer of moisture evaporates very quickly and evenly without causing large temperature fluctuations. This allows residual potassium nitrate and decomposition products to remain evenly on the particle surface and shortens the calcination time, avoiding the adverse effects of excessively long calcination times.

[0037] Preferably, the calcination temperature is 470-490℃, the concentration of the potassium nitrate solution is 11-13 wt%, and the mass ratio of potassium nitrate solution to coal gangue powder is 1:650-1:770. Using a relatively lower temperature, a relatively higher concentration of potassium nitrate solution, and a relatively lower mass ratio of potassium nitrate solution to coal gangue powder is more conducive to ensuring the matching of moisture evaporation and temperature under low-temperature conditions during preheating and the initial stage of calcination, thereby improving the activation effect and inhibiting the increase in the particle size of the ultrafine powder.

[0038] Furthermore, the potassium nitrate solution is sprayed using a high-pressure atomizing nozzle, with droplets larger than 100 μm (preferably 100-400 μm, 170-350 μm, 250-290 μm, etc.), and a spraying speed of 0.1-0.3 L / min (optionally 0.1 L / min, 0.2 L / min, 0.3 L / min, etc.). The high pressure (hereinafter the same) can be 2.3-6.4 MPa, etc. By using larger droplets, due to their smaller surface area / volume, their permeability is relatively weak, preventing immediate and excessive penetration into the deep layers of the powder and causing large-area gelatinization. Instead, local wetting is mainly formed at the contact points, which can effectively coordinate with the low-temperature conditions, allowing the contact between the potassium nitrate solution and the ultrafine powder, water evaporation, partial decomposition of potassium nitrate, and removal of organic matter to proceed gradually and controllably, which is more conducive to improving the activation effect and inhibiting the increase of the particle size of the ultrafine powder.

[0039] c) The material after the first stage of calcination is subjected to a second stage of calcination in the multi-stage suspension calcination reactor: calcination is carried out at a temperature of 900-950℃ (optionally 900℃, 907℃, 915℃, 918℃, 924℃, 927℃, 929℃, 931℃, 936℃, 938℃, 941℃, 945℃, 947℃, 948℃, 949℃, 950℃, etc.) for 10-15 minutes (preferably 11-13 minutes, etc.). High-temperature calcination facilitates further activation of the ultrafine powder and ensures the thorough conduct of reactions such as the dehydroxylation of kaolinite. By shortening the high-temperature stage, energy is saved, production efficiency is improved, and the driving force for particle size growth of the high-temperature sintered ultrafine powder is reduced. Short-time calcination effectively inhibits the formation of mullite and maximizes the retention of soluble amorphous SiO2 and the activity of silica reacting with calcium carbonate.

[0040] During this stage, a potassium carbonate solution with a concentration of 8-20 wt% (optional: 8wt%, 9wt%, 10wt%, 11wt%, 12wt%, 13wt%, 14wt%, 15wt%, 16wt%, 17wt%, 18wt%, 19wt%, 20wt%, etc.) is sprayed. The mass ratio of the potassium carbonate solution to the coal gangue powder is 1:500-1:600 ​​(optional: 1:500, 1:507, 1:513, 1:518, 1:522, 1:527, 1:531, 1:538, 1:542, 1:549, 1:555, 1:558, 1:567, 1:575, 1:584, 1:596, 1:600, etc.). The role of potassium carbonate in inhibiting sintering and further introducing nutrients: When the temperature reaches above 900℃ in the second stage, K2CO3 solution is sprayed in. The molten potassium salt covers the surface of the coal gangue particles, effectively preventing direct contact between particles, acting like a "separation film." This fundamentally prevents the sintering and agglomeration of ultrafine powder at high temperatures, effectively achieving the calcination of ultrafine powder and avoiding problems such as particle size increase and uneven distribution during high-temperature sintering. It also facilitates the introduction and improvement of the conversion ratio of nutrients such as K and N. In other words, the main function of adding potassium carbonate solution is to prevent particle growth problems such as sintering and agglomeration of ultrafine powder at high temperatures, and to facilitate reaction with components such as limestone, increasing the soluble silicon content. Using a relatively low proportion of potassium carbonate solution, resulting in a relatively high potassium carbonate content, can effectively save costs, inhibit particle growth during high-temperature calcination, reduce the amount of additives used, and reduce problems such as the high surface energy of ultrafine powder, which makes it more prone to agglomeration during high-temperature calcination. The relatively low proportion of potassium carbonate solution added avoids excessive water content, local over-wetting, uneven drying, local temperature drop, and agglomeration. It effectively ensures the matching of water evaporation and temperature under this condition. During the high-temperature calcination stage, it promotes the high-temperature melting of potassium carbonate. The high-temperature molten potassium carbonate on the surface of the ultrafine powder helps to reduce particle adhesion and growth, and also helps to shorten the calcination time, avoiding the adverse effects of excessive time.

[0041] The potassium carbonate solution is sprayed using a high-pressure atomizing nozzle, with droplet size of 10-50 μm (preferably 30-45 μm), and a spraying speed of 0.02-0.5 km / h. The spraying speed is L / min (preferably 0.31-0.49 L / min, 0.44-0.48 L / min, etc.). Potassium carbonate is sprayed using a high-pressure atomizing nozzle. The droplet size is close to the particle size of the ultrafine powder, facilitating uniform dispersion. Rapid droplet evaporation promotes interaction between potassium carbonate and ultrafine powder particles, effectively preventing direct contact between particles and preventing sintering and agglomeration of the ultrafine powder at high temperatures (possibly because potassium carbonate has a much higher melting point than potassium nitrate; the small droplets evaporate quickly, and the potassium carbonate is evenly dispersed on the surface of the ultrafine powder, partially decomposing and partially melting at high temperatures. The molten potassium carbonate remains on the surface of the ultrafine powder, reducing particle adhesion and growth). Controlling the droplet size facilitates the calcination of the ultrafine powder, avoiding problems such as increased particle size and uneven distribution during high-temperature sintering, and also helps to introduce and improve the conversion ratio of nutrients such as K and N. Excessively large droplet size (>50 μm): slow evaporation, a tendency for the ultrafine powder to increase in size, and reduced reactivity. Droplet size too small (<10μm): May be carried away by the airflow, reducing utilization rate, failing to effectively prevent direct contact between particles, and the ultrafine powder tends to increase in size. Spraying speed 0.02~0.5 L / min. Too fast a spraying speed: Droplets do not evaporate completely, leading to localized cooling, affecting melting and inhibiting adhesion, and the ultrafine powder tends to increase in size. Too slow a spraying speed: Insufficient droplet mixing power, affecting uniform mixing with the ultrafine powder, and the ultrafine powder tends to increase in size.

[0042] Preferably, the temperature of the second-stage calcination is 910-933℃, the concentration of the potassium carbonate solution is 15-17 wt%, and the mass ratio of potassium carbonate solution to coal gangue powder is 1:550-1:580. By using a relatively low high-temperature calcination temperature, a relatively high potassium carbonate content in the solution, and a relatively high spraying ratio, it is easier to avoid excessively high temperatures, which could hinder the growth of calcined particles and increase the proportion of molten potassium carbonate covering the particles, thus further suppressing the growth trend of ultrafine powder.

[0043] During the second-stage calcination, the gas introduced into the suspension calcination reactor contains 2-10% (preferably 4-9%, 6-8%, etc.) volume fraction of carbon dioxide. Introducing CO2 at a low flow rate increases the partial pressure of CO2, which helps suppress the decomposition of K2CO3, thereby increasing the proportion of molten potassium carbonate. This further enhances the barrier effect against direct contact between particles, suppressing the tendency of ultrafine powder to increase in size, and thus helping to increase the effective silicon content in the silicon fertilizer.

[0044] Before spraying, preheat the potassium carbonate solution to 60-80℃ (preferably 64-77℃, 71-76℃, etc.). Preheating the potassium carbonate solution facilitates the early evaporation of water vapor, thereby reducing the impact of water vapor on potassium carbonate. It also helps to further enhance the barrier effect between particles, inhibiting the growth of ultrafine powder and thus increasing the effective silicon content in the silicon fertilizer.

[0045] d) Collect the calcination products and separate the components rich in amorphous silica; use dry air separation at a wind speed of 8-12 m / s. Through separation, taking advantage of the loose and porous structure and low density (lower than alumina) of amorphous silica, and the dense structure and high density of corundum (α-Al2O3) and mullite crystalline phases that may be formed, a higher proportion of large particles can be obtained by further collecting components rich in amorphous silica, increasing the proportion of effective silicon, and increasing the effective components that react with limestone, which is beneficial to reducing Al damage (the harmful effects of excessive aluminum content in silicon fertilizer on plant growth).

[0046] e) The component rich in amorphous silica is mixed with limestone at a mass ratio of 4:6-8 (optionally 4:6, 4:7, or 4:8), and then processed to obtain coal gangue-based slow-release silicon fertilizer. Understandably, the processing of the component rich in amorphous silica with limestone can involve calcining the component rich in amorphous silica with limestone at a temperature above 1200℃ (e.g., 1250-1400℃, 1260-1310℃, 1270-1280℃, etc.) for 10-15 minutes to generate soluble calcium silicate, thereby increasing the effective silicon content in the silicon fertilizer.

[0047] The above method can be used to obtain coal gangue-based slow-release silicon fertilizer with a soluble silica content greater than 27% and a specific surface area greater than 30 m². 2 / g.

[0048] Preferably, the coal gangue-based slow-release silicon fertilizer contains potassium (K) and calcium (Ca), has a citric acid-soluble silicon content greater than 34%, and a specific surface area greater than 36 m². 2 / g.

[0049] The features and performance of this application will be further described in detail below with reference to embodiments:

[0050] Example 1

[0051] A method for preparing a coal gangue-based slow-release silicon fertilizer includes the following steps:

[0052] a) The coal gangue was crushed and subjected to ultrafine ball milling to obtain ultrafine coal gangue powder with a particle size D50 of 11 μm. The ultrafine ball milling was carried out using a planetary ball mill with a ball-to-material ratio of 17:1, a rotation speed of 358 rpm, and a milling time of 2.5 hours.

[0053] b) The ultrafine coal gangue powder is fed into a multi-stage suspension calcination reactor for a first stage of calcination: calcination is carried out at 471°C for 24 minutes. During this stage, a 12 wt% potassium nitrate solution is sprayed, with a mass ratio of potassium nitrate solution to coal gangue powder of 1:660. The potassium nitrate solution is sprayed using a high-pressure atomizing nozzle with a droplet size of 150 μm and a spraying rate of 0.2 L / min.

[0054] c) The material after the first stage of calcination is subjected to a second stage of calcination in the multi-stage suspension calcination reactor: calcination is carried out at 927°C for 12 minutes. During this stage, a 16 wt% potassium carbonate solution is sprayed, with a mass ratio of potassium carbonate solution to coal gangue powder of 1:575. The potassium carbonate solution is sprayed using a high-pressure atomizing nozzle, with droplet size of 35 μm and a spraying rate of 0.45 L / min. The gas introduced into the suspension calcination reactor during the second stage of calcination contains 7% carbon dioxide by volume. The potassium carbonate solution is preheated to 73°C before spraying.

[0055] d) Collect the calcination products and separate the components rich in amorphous silica; use dry air separation with a wind speed of 9 m / s.

[0056] e) The component rich in amorphous silica is mixed with limestone at a mass ratio of 4:6 and treated at 1270℃ to obtain coal gangue-based slow-release silicon fertilizer.

[0057] The above method yielded a coal gangue-based slow-release silicon fertilizer with a soluble silica content of 39% and a specific surface area of ​​39 m². 2 / g.

[0058] Example 2

[0059] The process is basically the same as in Example 1, with the main difference being that the ultrafine ball mill uses a planetary ball mill with a ball-to-material ratio of 8:1 and a rotation speed of 130 rpm.

[0060] The above method yielded a coal gangue-based slow-release silicon fertilizer with a soluble silica content of 35% and a specific surface area of ​​30 m². 2 / g.

[0061] Example 3

[0062] It is basically the same as Example 1, the main difference being that the calcination temperature of the first stage is 545°C.

[0063] The above method yielded a coal gangue-based slow-release silicon fertilizer with a soluble silica content of 38% and a specific surface area of ​​38 m². 2 / g.

[0064] Example 4

[0065] The method is basically the same as in Example 1, with the main difference being that the concentration of potassium nitrate solution is 6 wt% and the mass ratio of potassium nitrate solution to coal gangue powder is 1:200.

[0066] The above method yielded a coal gangue-based slow-release silicon fertilizer with a soluble silica content of 37% and a specific surface area of ​​36 m². 2 / g.

[0067] Example 5

[0068] The method is basically the same as in Example 1, with the main difference being that the concentration of the potassium nitrate solution is 15 wt% and the mass ratio of the potassium nitrate solution to the coal gangue powder is 1:970.

[0069] The above method yielded a coal gangue-based slow-release silicon fertilizer with a soluble silica content of 38% and a specific surface area of ​​37 m². 2 / g.

[0070] Example 6

[0071] It is basically the same as Example 1, the main difference being that the temperature of the second-stage calcination is 950°C.

[0072] The above method yielded a coal gangue-based slow-release silicon fertilizer with a soluble silica content of 39% and a specific surface area of ​​38 m². 2 / g.

[0073] Example 7

[0074] The method is basically the same as in Example 1, with the main difference being that the concentration of the potassium carbonate solution is 8 wt% and the mass ratio of the potassium carbonate solution to the coal gangue powder is 1:595.

[0075] The above method yielded a coal gangue-based slow-release silicon fertilizer with a soluble silica content of 38% and a specific surface area of ​​36 m². 2 / g.

[0076] Example 8

[0077] The method is basically the same as in Example 1, with the main difference being that the concentration of the potassium carbonate solution is 20 wt% and the mass ratio of the potassium carbonate solution to the coal gangue powder is 1:510.

[0078] The coal gangue-based slow-release silicon fertilizer obtained using the above method has a soluble silicon content of 39% and a specific surface area of ​​37 m². 2 / g.

[0079] Example 9

[0080] It is basically the same as Example 1, the main difference being that the carbon dioxide content during the second-stage calcination is the same as that in the air.

[0081] The above method yielded a coal gangue-based slow-release silicon fertilizer with a soluble silica content of 38% and a specific surface area of ​​36 m². 2 / g.

[0082] Example 10

[0083] The method is basically the same as in Example 1, with the main difference being that the potassium nitrate solution is sprayed using a high-pressure atomizing nozzle with a droplet size of 210 μm and a spraying speed of 0.05 L / min.

[0084] The above method yielded a coal gangue-based slow-release silicon fertilizer with a soluble silica content of 36% and a specific surface area of ​​34 m². 2 / g.

[0085] Example 11

[0086] The method is basically the same as in Example 1, with the main difference being that the potassium carbonate solution was not preheated before spraying.

[0087] The above method yielded a coal gangue-based slow-release silicon fertilizer with a soluble silica content of 38% and a specific surface area of ​​36 m². 2 / g.

[0088] Example 12

[0089] It is basically the same as Example 1, the main difference being that dry air sorting is used with a wind speed of 3m / s.

[0090] The above method yielded a coal gangue-based slow-release silicon fertilizer with a soluble silica content of 34% and a specific surface area of ​​33 m². 2 / g.

[0091] Comparative Example 1:

[0092] It is basically the same as Example 1, the main difference being that: no calcination and spraying of potassium nitrate solution were performed.

[0093] The above method yielded a coal gangue-based slow-release silicon fertilizer with a soluble silica content of 31% and a specific surface area of ​​30 m². 2 / g.

[0094] Comparative Example 2

[0095] It is basically the same as Example 1, the main difference being that potassium carbonate solution was not sprayed during the second stage of calcination.

[0096] The above method yielded a coal gangue-based slow-release silicon fertilizer with a soluble silica content of 33% and a specific surface area of ​​31 m². 2 / g.

[0097] Comparative Example 3

[0098] It is basically the same as Example 1, the main difference being that potassium nitrate was not sprayed during the first stage of calcination.

[0099] The above method yielded a coal gangue-based slow-release silicon fertilizer with a soluble silica content of 30% and a specific surface area of ​​29 m². 2 / g.

[0100] Comparative Example 4

[0101] The process is basically the same as in Example 1, with the main difference being that the droplet size of the sprayed potassium carbonate solution is 150 μm and the spraying speed is 0.01 L / min.

[0102] The above method yielded a coal gangue-based slow-release silicon fertilizer with a soluble silica content of 32% and a specific surface area of ​​30 m². 2 / g.

[0103] The preferred embodiments of the present invention have been described in detail above, and are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a coal gangue-based slow-release silicon fertilizer, characterized in that, Includes the following steps: a) The coal gangue is crushed and subjected to ultrafine ball milling to obtain ultrafine coal gangue powder with a particle size D50 of 5-15μm; b) The ultrafine coal gangue powder is fed into a multi-stage suspension calcination reactor for a first stage of calcination: calcination is carried out at 450-550℃ for 20-30 minutes, and a potassium nitrate solution with a concentration of 5-15 wt% is sprayed during this stage, with the mass ratio of potassium nitrate solution to coal gangue powder being 1:200 - 1:1000. c) The material after the first stage of calcination is subjected to a second stage of calcination in the multi-stage suspension calcination reactor: the temperature is raised to 900-950℃ and calcined for 10-15 minutes. During this stage, a potassium carbonate solution with a concentration of 8-20 wt% is sprayed. The mass ratio of potassium carbonate solution to coal gangue powder is 1:500-1:

600. The potassium carbonate solution is sprayed using a high-pressure atomizing nozzle with a droplet size of 10-50 μm and a spraying speed of 0.02-0.5 L / min. d) Collect the calcination products and separate out the components rich in amorphous silica; e) The component rich in amorphous silica is mixed with limestone at a mass ratio of 4:6-8, and then processed to obtain coal gangue-based slow-release silicon fertilizer.

2. The preparation method according to claim 1, characterized in that, In step a), the ultrafine ball milling adopts a planetary ball mill with a ball-to-material ratio of 10:1-20:1, a rotation speed of 250-400 rpm, and a ball milling time of 2-4 hours.

3. The preparation method according to claim 1, characterized in that, In step b), the calcination temperature is 470-490℃, the concentration of the potassium nitrate solution is 11-13 wt%, and the mass ratio of potassium nitrate solution to coal gangue powder is 1:650-1:

770.

4. The preparation method according to claim 1, characterized in that, In step c), the temperature of the second-stage calcination is 910-933℃, the concentration of the potassium carbonate solution is 15-17 wt%, and the mass ratio of potassium carbonate solution to coal gangue powder is 1:550-1:

580.

5. The preparation method according to claim 1, characterized in that, In step c), the gas introduced into the suspension calcination reactor during the second-stage calcination contains 2-10% by volume carbon dioxide.

6. The preparation method according to claim 1, characterized in that, In step b), the potassium nitrate solution is sprayed using a high-pressure atomizing nozzle with droplets larger than 100 μm and a spraying speed of 0.1-0.3 L / min.

7. The preparation method according to claim 1, characterized in that, In step c), the potassium carbonate solution is preheated to 60-80℃ before spraying.

8. The preparation method according to claim 1, characterized in that, In step d), dry air sorting is used with a wind speed of 8-12 m / s.

9. A coal gangue-based slow-release silicon fertilizer prepared by the preparation method according to any one of claims 1-8, characterized in that, Coal gangue-based slow-release silicon fertilizer has a citric acid-soluble silicon content greater than 27% and a specific surface area greater than 30 m². 2 / g.

10. The coal gangue-based slow-release silicon fertilizer according to claim 9, characterized in that, Coal gangue-based slow-release silicon fertilizer contains potassium (K) and calcium (Ca), with a citric acid content greater than 34% and a specific surface area greater than 36 m². 2 / g.