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

Abstract

The invention provides a slow-release silicon fertilizer prepared by using coal gangue as a raw material and a preparation method thereof, and the preparation method comprises the following steps: a) crushing coal gangue and carrying out ultrafine ball milling to obtain ultrafine coal gangue powder; b) feeding the superfine coal gangue powder into a multi-section suspension calcination reactor for first-section calcination: calcining at 450-550 DEG C, and spraying a potassium nitrate solution at the stage; c) second-stage calcination: a potassium carbonate solution with a concentration is sprayed at the stage, the spraying mode is a high-pressure atomizing nozzle, the liquid drop 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 according to a mass ratio of 4: (6-8), and treating to obtain the coal gangue-based slow-release silicon fertilizer. The method has the advantages that the calcining process can be accurately controlled, overburning and sintering are prevented, nutrient elements are synchronously introduced, the components are stable, and the slow-release effect is good.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of coal gangue resource recycling, and particularly relates to a slow-release silicon fertilizer prepared from coal gangue and a preparation method thereof. BACKGROUND

[0002] Coal gangue is a solid waste discharged in the process of coal mining and washing, and its main components are silicon oxide and aluminum oxide, and it also contains a small amount of iron oxide, calcium oxide, carbon and various trace elements. Large amounts of coal gangue stored not only occupy land, but also cause environmental pollution. One of the effective ways to realize the high value-added resource utilization of coal gangue is to prepare agricultural silicon fertilizer by calcining and activating the coal gangue. Silicon fertilizer can improve soil structure, promote crop growth and enhance stress resistance. Field tests show that the application of coal gangue silicon fertilizer can increase crop yield and improve crop quality. The crops treated by silicon fertilizer show stronger drought resistance, waterlogging resistance and disease and pest resistance, and reduce the use of pesticides, which meets the development direction of green agriculture. Long-term application can increase the cation exchange capacity of soil, promote the formation of granular structure and relieve soil compaction.

[0003] The silicon and aluminum elements in coal gangue mainly exist in the form of silicate minerals such as kaolinite (Al2Si2O2(OH)4) and illite, and the crystal structure is stable and difficult to dissolve in water, which cannot be directly absorbed by plants. It is necessary to destroy the crystal structure by high-temperature calcination to convert it into soluble amorphous active SiO2 and Al2O3. However, in the traditional fixed bed or rotary kiln calcination process, due to the low heat transfer efficiency and uneven heating of the material, it is easy to cause "overburning" or "sintering". So-called "overburning" refers to the fact that the calcination temperature is too high or the time is too long, which causes the vitrification of the surface of the material particles and the closure of the pores, reducing the active sites. When sintering, the coal gangue particles will stick to each other to form a dense block, not only causing a sharp increase in subsequent crushing energy consumption, but also wrapping the effective ingredients and blocking the pore structure, so that it loses the specific surface area and pore volume required as a fertilizer, and has poor water and fertilizer retention capacity. In the prior art, the coal gangue and the organic solid waste are crushed respectively to obtain coal gangue powder and organic solid waste powder; the coal gangue powder and the organic solid waste powder are mixed to obtain a mixture; the mixture is sequentially subjected to pyrolysis treatment, calcination and stabilization to obtain an activated material; and the activated material is sequentially subjected to quenching and crushing to obtain the silicon fertilizer. However, due to the difficulty in controlling the composition of the organic solid waste, the quality of the finished product is difficult to stabilize, the effective silicon content fluctuates greatly, and the effective compound of K and other elements cannot be realized, the silicon particle porosity is not rich, and the like, which affects the slow-release effect and the fertility. In the prior art, the composition of the multi-effect water-soluble silicon fertilizer includes silicon-containing waste residue and an activator. The silicon activator is a mixture of potassium carbonate and calcium carbonate, containing multiple nutrients such as silicon, potassium and calcium, which has a good effect on improving soil fertility, improving the environment of contaminated farmland soil and promoting crop yield. However, the actual effective silicon content is low, which affects the utilization rate of Si, K and the slow-release effect.

[0004] Therefore, the prior art has the problems of poor slow-release effect of silicon fertilizer, single chemical element, unstable product composition, especially effective silicon content, and difficult to stabilize and control the product quality. Therefore, it is of great significance to develop a new technology for preparing silicon fertilizer from coal gangue, which can accurately control the calcination process, prevent overburning and sintering, and simultaneously introduce nutrient elements, has stable composition and good slow-release effect, for realizing high-value resource utilization of coal gangue and developing green agriculture. SUMMARY

[0005] To overcome the shortcomings of the prior art, the present application provides a coal gangue-based slow-release silicon fertilizer and a preparation method thereof, which has the advantages of being able to accurately control the calcination process, prevent overburning and sintering, and simultaneously introduce nutrient elements, has stable composition and good slow-release effect.

[0006] Embodiments of the present application are implemented as follows: In a first aspect, the present application provides a preparation method of a coal gangue-based slow-release silicon fertilizer, comprising the following steps: a) crushing and ultrafine ball milling coal gangue to obtain ultrafine coal gangue powder with a particle size D50 of 5-15 μm; b) feeding the ultrafine coal gangue powder into a multi-stage suspension calcination reactor for one-stage calcination: calcining at 450-550℃ for 20-30 minutes, and spraying a potassium nitrate solution with a concentration of 5-15 wt% at this stage, the mass ratio of the potassium nitrate solution to the coal gangue powder being 1:200-1:1000; c) carrying out two-stage calcination on the one-stage calcined material in the multi-stage suspension calcination reactor: calcining at 900-950℃ for 10-15 minutes, and spraying a potassium carbonate solution with a concentration of 8-20 wt% at this stage, the mass ratio of the potassium carbonate solution to the coal gangue powder being 1:500-1:600, the spraying mode being a high-pressure atomizing nozzle, the droplet size being 10-50 μm, and the spraying speed being 0.02-0.5 L / min; d) collecting the calcination product and sorting out the component rich in amorphous silicon oxide; e) mixing the component rich in amorphous silicon oxide with limestone at a mass ratio of 4:6-8, and obtaining a coal gangue-based slow-release silicon fertilizer through processing.

[0007] Optionally, in step a), the ultrafine ball milling uses a planetary ball mill, the ball-to-material ratio is 10:1-20:1, the rotation speed is 250-400 rpm, and the ball milling time is 2-4 hours.

[0008] Optionally, in step b), the one-stage calcination temperature is 470-490℃, the concentration of the potassium nitrate solution is 11-13 wt%, and the mass ratio of the potassium nitrate solution to the coal gangue powder is 1:650-1:770.

[0009] Optionally, in step c), the two-stage calcination temperature is 910-933℃, the concentration of the potassium carbonate solution is 15-17 wt%, and the mass ratio of the potassium carbonate solution to the coal gangue powder is 1:550-1:580.

[0010] Optionally, in step c), the gas introduced into the suspension calcination reactor during the two-stage calcination contains 2-10% by volume of carbon dioxide.

[0011] Optionally, in step b), the spraying mode of the potassium nitrate solution is a high-pressure atomizing nozzle, the droplet size is greater than 100 μm, and the spraying speed is 0.1-0.3 L / min.

[0012] Optionally, in step c), the potassium carbonate solution is preheated to 60-80℃ before spraying.

[0013] Optionally, in step d), a dry air separation is used, and the air speed is 8-12 m / s.

[0014] In the first aspect, the application provides a coal gangue-based slow-release silicon fertilizer prepared by the above preparation method, the coal gangue-based slow-release silicon fertilizer has a content of silicate solubility greater than 27% and a specific surface area greater than 30 m 2 / g.

[0015] Preferably, the coal gangue-based slow-release silicon fertilizer contains K and Ca elements, has a content of silicate solubility greater than 34% and a specific surface area greater than 36 m 2 / g.

[0016] Beneficial effects include: (1) Multi-stage suspension calcination and gradient temperature control: Suspension calcination allows the superfine material to fully and quickly exchange heat with hot air, avoiding local overheating. The first stage temperature of 450-550°C aims to decompose the kaolinite structure and part of the organic matter in the coal gangue. The low temperature in this stage takes into account the activation efficiency while avoiding the initial sintering of the superfine material. Subsequently, the temperature is raised to a higher temperature (900-950°C) to complete the complete activation of the silicon structure. The gradient temperature rising method thermodynamically inhibits the occurrence of overburning crystallization, especially for superfine materials, a lower temperature is used, the difference between the high and low temperature intervals is increased, which is beneficial to the full and rapid uniform reaction of the superfine material, avoiding the problems of overburning crystallization of the superfine material, aggregation and growth of the superfine material during the calcination and activation process, and large particle size fluctuations. Thus, it is beneficial to generate a silicon fertilizer with rich pores and effective silicon content after being treated by calcination with limestone, fully reacting with limestone.

[0017] (2) KNO3 reaming and oxidation: KNO3 solution is sprayed in the first stage of 450-550℃, KNO3 decomposes rapidly at this temperature: 2KNO3→2KNO2+O2↑, and further decomposes 2KNO3→K2O+NO↑+NO2↑ (or O2↑). Taking advantage of the low decomposition temperature of KNO3, the generated O2, NO, NO2 and other gases "explode" inside the coal gangue particles, effectively cooperating with low-temperature calcination to open up and expand the particle's micropore channels, creating a rich mesoporous and macroporous structure, effectively improving the specific surface area of the finished product, high-temperature activity and reactivity, which is conducive to reaction with K, calcium oxide and other components, increasing the content of water-soluble active silicon and water-soluble available K-containing silicon fertilizer such as potassium silicate (in existing technologies, potassium carbonate and other components are generally added, and the actual effective plant utilization of potassium in the generated silicon fertilizer is low, resulting in high cost, even causing silicon fertilizer residues such as alkaline substances, increasing the risk of soil alkalization, and forming alkali harm). At the same time, the newly formed oxygen and nitrogen oxides react with residual carbon and organic matter in the coal gangue, increasing the reactivity of carbon oxidation exothermic, improving the porosity of gasification, and retaining nitrogen in the silicon fertilizer composition. Available nitrogen components can provide a "cleaner" silicon aluminum matrix (i.e. further reducing non-usable components) for the subsequent high-temperature stage, avoiding incomplete reaction and impurity wrapping caused by carbon, and facilitating the introduction and improvement of the conversion ratio of nutrient elements potassium.

[0018] (3) K2CO3 sintering prevention and nutrient further introduction: K2CO3 solution is sprayed when the second stage temperature reaches 900℃ or above, and the molten potassium salt covers the surface of the coal gangue particles, effectively preventing direct contact between particles, like a layer of "isolation film", fundamentally preventing the sintering and bonding of ultra-fine powders at high temperatures, effectively realizing the calcination of ultra-fine powders, avoiding the problem of increasing particle size and uneven distribution of ultra-fine powders during high-temperature sintering, and facilitating the introduction and improvement of the conversion ratio of K, N and other nutrient elements.

[0019] (4) The spraying method of potassium carbonate is high-pressure atomizing nozzle, and the droplet size is 10-50 μm, which is close to the particle size of superfine powder, and is beneficial to uniform dispersion and realization of spraying. The droplet evaporates quickly, which is beneficial to the interaction between potassium carbonate and superfine powder particles, improves the effective blocking of direct contact between particles, and is beneficial to preventing sintering and bonding of superfine powder at high temperature (the possible reason is that the melting point of potassium carbonate is much higher than that of potassium nitrate, the small droplet is sprayed, the droplet evaporates quickly, potassium carbonate is uniformly dispersed on the surface of superfine powder, part of which is decomposed, part of which is melted at high temperature, and part of the high-temperature melted potassium carbonate is on the surface of the superfine powder, which is beneficial to reducing the particle adhesion and growth). The droplet size is controlled to be beneficial to the calcination of superfine powder, avoiding the problems of particle size increase and uneven distribution of superfine powder during high-temperature sintering, and improving the conversion ratio of K, N and other nutrient elements. If the droplet size is too large (> 50 μm), the evaporation is slow, the superfine powder tends to increase, and the reactivity decreases. If the droplet size is too small (< 10 μm), it may be carried away by the gas flow, reducing the utilization rate, and cannot realize the effective blocking of direct contact between particles. The superfine powder tends to increase. The spraying speed is 0.02-0.5 L / min, and if the spraying speed is too fast, the droplet has not been completely evaporated, which leads to local cooling, affects melting, and affects adhesion inhibition. The superfine powder tends to increase. If the spraying speed is too slow, the droplet mixing power is insufficient, which affects the uniform mixing with the superfine powder, and the superfine powder tends to increase.

[0020] The present application solves the core problems of deactivation and sintering by physical superfine crushing activation, multi-stage suspension calcination multi-step multi-temperature activation, chemical additive spraying to reduce the risk of particle size increase, and improves the activation conditions. In addition, the present application not only solves the core problems of deactivation and sintering, but also constructs a multi-level pore structure, greatly improves the specific surface area and pore volume of the product, and has excellent water and fertilizer retention and slow-release performance. The added K and other nutrient elements are efficiently converted into available potassium silicate and other components, which are directly integrated into the product, improving the utilization of silicon, K and other elements, improving the fertilizer efficiency, and avoiding the increase of harmful component residues. By mixing with limestone, the compound with limestone is further improved, the slow-release rate of silicon fertilizer is further controlled, and long-acting fertilizer supply is realized. DETAILED DESCRIPTION

[0021] The technical solutions of the present application will be described below in conjunction with the embodiments. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor belong to the scope of protection of the present application.

[0022] As used herein, and unless the context dictates otherwise, all terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. The reagents used herein can be commercially available related products, and the performance test standards refer to the industry or national standards.

[0023] As used herein, and unless the context dictates otherwise, all terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. The reagents used herein can be commercially available related products, and the performance test standards refer to the industry or national standards.

[0024] The prior art has the problems of poor slow-release effect of silicon fertilizer, single chemical element, unstable product composition especially effective silicon content, and difficult stable control of product quality. Embodiments of the present application provide a coal gangue-based slow-release silicon fertilizer and a preparation method thereof.

[0025] An exemplary preparation method of a coal gangue-based slow-release silicon fertilizer is provided, which comprises the following steps: a) crushing and performing superfine ball milling on the coal gangue to obtain superfine coal gangue powder with a particle size D50 of 5-15 μm (preferably 13-15 μm, and optionally 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 11 μm, 12 μm, 13 μm, 15 μm, etc.); by using superfine ball milling on the coal gangue, part of the ball milling energy is converted into internal energy of the material during the ball milling process, resulting in distortion of the crystal lattice, dislocation, amorphization and other defects, shortening of the diffusion path inside the particles, and easier migration of atoms and ions, thereby facilitating low-temperature activation and significantly improving the conversion rate and dissolution rate of effective silicon.

[0026] The ultra-fine ball milling adopts a planetary ball mill, the ball-to-material ratio is 10:1-20:1 (which can be selected as 10:1, 11:1, 12:1, 13:1, 14:1, 15:1, 16:1, 17:1, 18:1, 20:1, etc.), the rotation speed is 250-400 rpm (preferably: 330-360 rpm, 355-360 rpm, etc.), and the ball milling time is 2-4 hours. By adopting high ball-to-material ratio and high rotation speed, sufficient energy input and collision frequency are provided to improve the lattice distortion, dislocation, amorphization and other defects, realize physical activation, and high rotation speed can make the grinding medium in high-efficiency throwing impact mode, avoid the problems such as adhesion of ultra-fine powder caused by low speed, and cause uneven particle size distribution.

[0027] b) The ultra-fine coal gangue powder is sent into a multi-stage suspension calcination reactor for one-stage calcination: calcination at 450-550°C (preferably 457-496°C, 467-483°C, etc.) for 20-30 minutes (preferably 21-26 minutes, etc.), and the first-stage low-temperature temperature is aimed at decomposing the kaolinite structure and part of the organic matter in the coal gangue. This stage adopts low-temperature temperature to consider the activation efficiency while avoiding the initial sintering of the micron-sized particle size of the ultra-fine material (the kaolinite structure and part of the organic matter in the coal gangue, especially part of the organic matter, has the trend of increasing the particle size when heated and decomposed, especially the possible reasons such as adhesion and other causes leading to particle size increase under high temperature rapid heating). By adopting ultra-fine ball milling of coal gangue, part of the ball milling energy is converted into internal energy of the material during the ball milling process, resulting in lattice distortion, dislocation, amorphization and other defects, the diffusion path inside the particles is shortened, and atoms and ions are more easily migrated. By utilizing the above characteristics of ultra-fine particles, the low-temperature temperature considers the efficiency while achieving better pre-activation effect, and shorter calcination time can be adopted at this time, which improves the efficiency.

[0028] In this stage, a potassium nitrate solution with a concentration of 5-15 wt% (preferably 6-14 wt%, 7-11 wt%, etc.) is sprayed, and the mass ratio of the potassium nitrate solution to the coal gangue powder is 1:200-1:1000 (preferably 1:330-1:860, 1:460-1:790, 1:580-1:780, etc.). The reaming and oxidation of potassium nitrate: spray KNO3 solution in a temperature range of 450-550°C, KNO3 rapidly decomposes at this temperature: 2KNO3→2KNO2+O2↑, and further decomposes 2KNO3→K2O+NO↑+NO2↑ (or O2↑). Taking advantage of the low decomposition temperature of KNO3, the generated O2, NO, NO2, etc. "explosively" overflow inside the coal gangue particles, effectively cooperating with low-temperature calcination to open up and expand the micropore channels of the particles, which is beneficial to the rapid removal of non-usable carbon and organic matter, creating abundant mesoporous and macroporous structures, effectively improving the specific surface area, high-temperature activation, and reactivity of the finished product, which is conducive to reaction with K, calcium oxide, and other components, increasing the content of water-soluble active silicon and water-soluble usable K-containing silicon fertilizer such as potassium silicate (in existing technologies, the content of potassium carbonate is generally added, and the actual effective plant-available potassium content in the generated silicon fertilizer is low, resulting in high cost, even causing silicon fertilizer residues such as alkaline substances, increasing the risk of soil alkalization, and forming alkali damage). At the same time, the newly formed oxygen and nitrogen oxides react with the residual carbon and organic matter in the coal gangue, increasing the heat release of carbon oxidation and improving the reactivity, gasification, and porosity, and the nitrogen-containing components in the silicon fertilizer can be utilized, providing a "cleaner" silicon-aluminum matrix (i.e., further reducing non-usable components) for the subsequent high-temperature stage, avoiding incomplete reactions and impurity wrapping caused by carbon, and facilitating the introduction and improvement of the conversion ratio to form the nutrient element potassium. By using a relatively low proportion of potassium nitrate solution with a relatively high content of potassium nitrate, the cost can be effectively saved, the activation effect can be achieved, the amount of additives can be reduced, and the problems of super-fine powder, such as high surface energy, large sintering driving force, and easy agglomeration, can be avoided. Avoiding excessive water, local over-wetting, uneven drying, local temperature drop, and even agglomeration, a relatively small proportion of super-fine powder can effectively ensure the matching of water evaporation and temperature under low-temperature conditions. In the preheating and calcination initial stage, the thin layer of water can be evaporated very quickly and uniformly, without causing large temperature fluctuations, which is beneficial to the uniform distribution of residual potassium nitrate and decomposition products on the particle surface, and also helps to shorten the calcination time and avoid the adverse effects of excessive time.

[0029] Preferably, the temperature of the first calcination is 470-490℃, the concentration of the potassium nitrate solution is 11-13 wt%, and the mass ratio of the potassium nitrate solution to the coal gangue powder is 1:650-1:770. Using a relatively lower temperature, a relatively higher concentration of the potassium nitrate solution, and a relatively lower mass ratio of the potassium nitrate solution to the coal gangue powder, it is more conducive to the evaporation of water and the matching of the temperature under low-temperature conditions in the preheating and initial calcination stages, improves the activation effect, and inhibits the increase in the particle size of the superfine powder.

[0030] Further, the spraying mode of the potassium nitrate solution is a high-pressure atomizing nozzle, the liquid droplets are greater than 100 μm (preferably 100-400 μm, 170-350 μm, 250-290 μm, etc.), and the spraying speed is 0.1-0.3 L / min (optionally 0.1 L / min, 0.2 L / min, 0.3 L / min, etc.). The high pressure (the same below) can be 2.3-6.4 MPa, etc. By using larger liquid droplets, the penetration is relatively weak due to the small surface area / volume ratio, and the large-area pasting caused by immediate and excessive penetration into the deep layer of the powder is avoided, and local wetting is mainly formed at the contact points, so that the processes of the contact between the potassium nitrate solution and the superfine powder, water evaporation, partial decomposition of the potassium nitrate solution, and removal of organic matter under low-temperature conditions can be gradually and controllably performed, which is more conducive to improving the activation effect and inhibiting the increase in the particle size of the superfine powder. c) The material after the first calcination is subjected to the second calcination in the multi-stage suspension calcination reactor: the temperature is raised to 900-950℃ (optionally 900℃, 907℃, 915℃, 918℃, 924℃, 927℃, 929℃, 931℃, 936℃, 938℃, 941℃, 945℃, 947℃, 948℃, 949℃, 950℃, etc.), and the calcination is performed for 10-15 minutes (preferably 11-13 minutes, etc.). The high-temperature calcination is conducive to the further activation of the superfine powder and the complete reaction of the dehydroxylation of kaolinite. By shortening the time of the high-temperature stage, the energy is saved, the production efficiency is improved, the driving force for the increase in the particle size of the sintered superfine powder is reduced, the generation of mullite is effectively inhibited by short-time calcination, and the activity of the soluble amorphous SiO2 and the silica for the reaction with calcium carbonate is maximized.

[0031] In this stage, the spraying concentration of potassium carbonate solution is 8-20 wt% (optionally 8 wt%, 9 wt%, 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, 15 wt%, 16 wt%, 17 wt%, 18 wt%, 19 wt%, 20 wt%, etc.), and the mass ratio of potassium carbonate solution to coal gangue powder is 1:500-1:600 (optionally 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 sintering resistance and further introduction of nutrients of potassium carbonate: when the temperature in the second section reaches 900°C or above, K2CO3 solution is sprayed, and the molten potassium salt covers the surface of the coal gangue particles, effectively preventing direct contact between particles, like a layer of "isolation film", fundamentally preventing the sintering and bonding of superfine powder at high temperature, effectively realizing the calcination of superfine powder, avoiding the problems of particle size increase and uneven distribution of superfine powder during high temperature sintering, and facilitating the introduction and improvement of the conversion ratio of K, N and other nutrient elements. That is, the addition of potassium carbonate solution mainly prevents the sintering and bonding of superfine powder at high temperature, which is beneficial to the reaction with limestone and other components, and improves the soluble silicon content. By using a relatively low proportion of potassium carbonate solution, the potassium carbonate content in the potassium carbonate solution is relatively high, which can effectively save costs, prevent the growth of particles during high temperature calcination, reduce the amount of additives used, and reduce the problems of superfine powder aggregation due to high surface energy and high sintering driving force during high temperature calcination. The relatively low proportion of potassium carbonate solution avoids excessive water, local over-wetting, uneven drying, local temperature drop, and agglomeration, which can effectively ensure the matching of water evaporation and temperature under this temperature condition, promote the high temperature melting of potassium carbonate during high temperature calcination, and facilitate the reduction of particle adhesion and growth, as well as the shortening of calcination time to avoid the adverse effects of long time.

[0032] The spraying method of the potassium carbonate solution is high-pressure atomizing nozzle, the droplet size is 10-50 μm (preferably 30-45 μm, etc.), the spraying speed is 0.02-0.5 L / min (preferably 0.31-0.49 L / min, 0.44-0.48 L / min, etc.); the spraying method of potassium carbonate is high-pressure atomizing nozzle, the droplet size is close to the particle size of the superfine powder, which is beneficial to the uniform dispersion of the spraying, the droplet evaporates quickly, which is beneficial to the interaction between potassium carbonate and superfine powder particles, improves the effective blocking of the direct contact between particles, and is beneficial to prevent the sintering and bonding of superfine powder at high temperature (the possible reason is that the melting point of potassium carbonate is much higher than that of potassium nitrate, the small droplet is evaporated quickly, potassium carbonate is uniformly dispersed on the surface of the superfine powder, part of which is decomposed, part of which is melted at high temperature, and part of the high-temperature melted potassium carbonate is on the surface of the superfine powder, which is beneficial to reduce the particle adhesion and growth), the droplet size control is beneficial to the calcination of the superfine powder, avoids the increase of the particle size of the superfine powder and the uneven distribution during high-temperature sintering, and is beneficial to the introduction and improvement of the conversion ratio of K, N and other nutrient elements. If the droplet size is too large (> 50 μm): the evaporation is slow, the superfine powder tends to increase, and the reactivity decreases. If the droplet size is too small (< 10 μm): it may be carried away by the gas flow, reducing the utilization rate, and cannot effectively block the direct contact between particles, etc., and the superfine powder tends to increase. If the spraying speed is too fast (0.02-0.5 L / min): the droplet is not completely evaporated, which leads to local cooling, affecting the melting and inhibiting adhesion, and the superfine powder tends to increase. If the spraying speed is too slow: the droplet mixing power is insufficient, which affects the uniform mixing with the superfine powder, and the superfine powder tends to increase.

[0033] 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 the potassium carbonate solution to the 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 more beneficial to avoid high temperature, calcination particle growth power, increase the melting of potassium carbonate to cover the particle ratio, and further inhibit the increase of the superfine powder.

[0034] The gas introduced into the suspension calcination reactor during the second-stage calcination contains 2-10% (preferably 4-9%, 6-8%, etc.) volume fraction of carbon dioxide. Introducing low flow rate CO2 increases the CO2 partial pressure, which is beneficial to inhibit the decomposition of K2CO3, thereby increasing the proportion of molten potassium carbonate, further improving the effect of blocking the direct contact between particles, and inhibiting the increase of the superfine powder, thereby improving the effective silicon content in the silicon fertilizer.

[0035] The potassium carbonate solution is preheated to 60-80°C (preferably 64-77°C, 71-76°C, etc.) before spraying. By preheating the potassium carbonate solution content, the water vapor is volatilized in advance, thereby reducing the influence of water vapor on potassium carbonate, further improving the direct contact between barrier particles, etc., inhibiting the trend of increasing superfine powder, thereby improving the effective silicon content in the silicon fertilizer.

[0036] d) Collecting the calcined product and sorting out the amorphous silicon oxide-rich component; dry air separation is used, with a wind speed of 8-12 m / s. Through separation, the amorphous silicon oxide structure is loose, porous, and has low density (lower than aluminum oxide), while corundum (α-Al2O3) and possible mullite crystal phases have dense structure, high density, and a high proportion of large particles, etc. The amorphous silicon oxide-rich component can be further collected to improve the effective silicon proportion and the effective ingredient for reaction with limestone, thereby reducing Al damage (excessive aluminum content in the silicon fertilizer causing adverse effects on plant growth).

[0037] e) Mixing the amorphous silicon oxide-rich component with limestone at a mass ratio of 4:6-8 (optionally 4:6, 4:7, 4:8), and treating to obtain a coal gangue-based slow-release silicon fertilizer. Understandably, the amorphous silicon oxide-rich component and limestone can be calcined at a ratio of 1200°C (for example, 1250-1400°C, 1260-1310°C, 1270-1280°C, etc.) for 10-15 minutes to generate soluble calcium silicate, thereby improving the effective silicon content in the silicon fertilizer.

[0038] The coal gangue-based slow-release silicon fertilizer obtained by the above method has a water-soluble silicon content of greater than 27% and a specific surface area of greater than 30 m 2 / g.

[0039] Preferably, the coal gangue-based slow-release silicon fertilizer contains K and Ca elements, has a water-soluble silicon content of greater than 34%, and a specific surface area of greater than 36 m 2 / g.

[0040] The features and performance of the present application are further described in detail below in conjunction with the following examples: Example 1 A preparation method of a coal gangue-based slow-release silicon fertilizer, comprising the following steps: a) crushing the coal gangue and performing superfine ball milling to obtain superfine coal gangue powder with a particle size D50 of 11 μm; the superfine ball milling is performed using a planetary ball mill, with a ball-to-material ratio of 17:1, a rotation speed of 358 rpm, and a ball milling time of 2.5 hours.

[0041] b) The superfine coal gangue powder is fed into a multi-stage suspension calcination reactor for one-stage calcination: calcination at 471℃ for 24 minutes, and a potassium nitrate solution with a concentration of 12 wt% is sprayed in the stage, the mass ratio of potassium nitrate solution to coal gangue powder being 1:660. The potassium nitrate solution is sprayed by a high-pressure atomizing nozzle, the liquid droplet size being 150 μm, and the spraying speed being 0.2 L / min.

[0042] c) The one-stage calcination product is subjected to two-stage calcination in the multi-stage suspension calcination reactor: calcination at 927℃ for 12 minutes, and a potassium carbonate solution with a concentration of 16 wt% is sprayed in the stage, the mass ratio of potassium carbonate solution to coal gangue powder being 1:575. The potassium carbonate solution is sprayed by a high-pressure atomizing nozzle, the liquid droplet size being 35 μm, and the spraying speed being 0.45 L / min. The gas fed into the suspension calcination reactor during the two-stage calcination contains 7% by volume of carbon dioxide. The potassium carbonate solution is preheated to 73℃ before spraying.

[0043] d) The calcination product is collected, and the component rich in amorphous silicon oxide is separated out; dry air separation is used, and the wind speed is 9 m / s.

[0044] e) The component rich in amorphous silicon oxide is mixed with limestone at a mass ratio of 4:6, and coal gangue-based slow-release silicon fertilizer is obtained by treatment at 1270℃.

[0045] The coal gangue-based slow-release silicon fertilizer obtained by the above method has a water-soluble silicon content of 39%, and a specific surface area of 39 m 2 / g.

[0046] Example 2 The example is basically the same as Example 1, and the main difference is that a planetary ball mill is used for superfine ball milling, the ball-to-material ratio is 8:1, and the rotation speed is 130 rpm.

[0047] The coal gangue-based slow-release silicon fertilizer obtained by the above method has a water-soluble silicon content of 35%, and a specific surface area of 30 m 2 / g.

[0048] Example 3 The example is basically the same as Example 1, and the main difference is that the one-stage calcination temperature is 545℃.

[0049] The coal gangue-based slow-release silicon fertilizer obtained by the above method has a water-soluble silicon content of 38%, and a specific surface area of 38 m 2 / g.

[0050] Example 4 The example is basically the same as Example 1, and the main difference is that the concentration of the potassium nitrate solution is 6 wt%, and the mass ratio of potassium nitrate solution to coal gangue powder is 1:200.

[0051] The coal gangue-based slow-release silicon fertilizer obtained by the above method has a citric acid-soluble silicon content of 37%, a specific surface area of 36 m 2 / g.

[0052] Example 5 Based on the same as example 1, the main difference is 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.

[0053] The coal gangue-based slow-release silicon fertilizer obtained by the above method has a citric acid-soluble silicon content of 38%, a specific surface area of 37 m 2 / g.

[0054] Example 6 Based on the same as example 1, the main difference is that the temperature of the two-stage calcination is 950°C.

[0055] The coal gangue-based slow-release silicon fertilizer obtained by the above method has a citric acid-soluble silicon content of 39%, a specific surface area of 38 m 2 / g.

[0056] Example 7 Based on the same as example 1, the main difference is 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.

[0057] The coal gangue-based slow-release silicon fertilizer obtained by the above method has a citric acid-soluble silicon content of 38%, a specific surface area of 36 m 2 / g.

[0058] Example 8 Based on the same as example 1, the main difference is 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.

[0059] The coal gangue-based slow-release silicon fertilizer obtained by the above method has a citric acid-soluble silicon content of 39%, a specific surface area of 37 m 2 / g.

[0060] Example 9 Based on the same as example 1, the main difference is that the carbon dioxide content during the two-stage calcination is the content in the air.

[0061] The coal gangue-based slow-release silicon fertilizer obtained by the above method has a citric acid-soluble silicon content of 38%, a specific surface area of 36 m 2 / g.

[0062] Example 10 Based on the same as example 1, the main difference is that the way of spraying the potassium nitrate solution is a high-pressure atomizing nozzle, the droplet size is 210 μm, and the spraying speed is 0.05 L / min.

[0063] The coal gangue-based slow-release silicon fertilizer obtained by the above method has a citric-soluble silicon content of 36%, a specific surface area of 34 m 2 / g.

[0064] Example 11 Based on the same as Example 1, the main difference is that the potassium carbonate solution is not preheated before spraying.

[0065] The coal gangue-based slow-release silicon fertilizer obtained by the above method has a citric-soluble silicon content of 38%, a specific surface area of 36 m 2 / g.

[0066] Example 12 Based on the same as Example 1, the main difference is that dry air separation is used, with a wind speed of 3 m / s.

[0067] The coal gangue-based slow-release silicon fertilizer obtained by the above method has a citric-soluble silicon content of 34%, a specific surface area of 33 m 2 / g.

[0068] Comparative Example 1 Based on the same as Example 1, the main difference is that the first-stage calcination and spraying of the potassium nitrate solution are not performed.

[0069] The coal gangue-based slow-release silicon fertilizer obtained by the above method has a citric-soluble silicon content of 31%, a specific surface area of 30 m 2 / g.

[0070] Comparative Example 2 Based on the same as Example 1, the main difference is that the second-stage calcination is not sprayed with the potassium carbonate solution.

[0071] The coal gangue-based slow-release silicon fertilizer obtained by the above method has a citric-soluble silicon content of 33%, a specific surface area of 31 m 2 / g.

[0072] Comparative Example 3 Based on the same as Example 1, the main difference is that the first-stage calcination is not sprayed with the potassium nitrate.

[0073] The coal gangue-based slow-release silicon fertilizer obtained by the above method has a citric-soluble silicon content of 30%, a specific surface area of 29 m 2 / g.

[0074] Comparative Example 4 Based on the same as Example 1, the main difference is that the spraying of the potassium carbonate solution has a droplet size of 150 μm and a spraying speed of 0.01 L / min.

[0075] The coal gangue-based slow-release silicon fertilizer obtained by the above method has a citric-soluble silicon content of 32%, a specific surface area of 30 m 2 / g.

[0076] The above describes the preferred embodiments of the present application, only to illustrate the technical solutions of the present application, rather than limit them; although the present application is described in detail with reference to the foregoing embodiments, those skilled in the art should understand that the technical solutions recorded in the foregoing embodiments can still be modified, or some or all of the technical features can be replaced by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

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.