Slow-release potash fertilizer with sustained and controlled release function and soil improvement function and preparation method thereof

Abstract

The invention relates to the technical field of slow-release fertilizers, and particularly discloses a slow-release potash fertilizer with a sustained-release function and a soil improvement function as well as a preparation method and application of the slow-release potash fertilizer. According to the preparation method, the powdery potash fertilizer and the superfine mineral particles are blended and bonded by the binder to form the potash fertilizer particles, and meanwhile, the specific isocyanate and the biological polyol are matched to form the pre-polymerized coating liquid to coat the potash fertilizer particles for multiple times, so that the finally prepared blended coated potash fertilizer has an excellent slow release characteristic; a super-long nutrient slow-release period is achieved, and potassium elements can be stably and continuously supplied to crops in the growth stage; and secondly, the slow-release potash fertilizer provided by the invention also shows excellent degradation performance, can quickly realize degradation and conversion at an efficient rate, and greatly reduces the negative influence of coating residues on the environment. Therefore, the problems that a traditional potash fertilizer is short in slow release life and unbalanced in nutrient supply are solved, and a solid and reliable theoretical support is provided for the whole growth and development process of crops such as cherry tomatoes and the like.

Description

Technical Field

[0001] This application relates to the field of slow-release fertilizer technology, and in particular to a slow-release potassium fertilizer with slow-release and soil-improving functions and its preparation method. Background Technology

[0002] Potassium is the third most essential macronutrient for plant growth and metabolism, after nitrogen and phosphorus. In the physiological and ecological systems of plants, potassium plays an indispensable role in several key processes, including photosynthesis, respiration, the maintenance of normal enzyme function, and the enhancement of stress resistance. Potassium deficiency in plants can trigger a series of negative effects, such as hindered root development, slowed growth rate, weakened disease resistance, delayed maturity, decreased seed yield, and overall reduced yield. Conversely, the rational application of potassium fertilizer can effectively improve crops' resistance to disease, drought, and lodging, providing strong support for increased crop yield and improved quality.

[0003] As a major agricultural country, China faces a relative scarcity of potash resources. Domestic potash fertilizer production is far from sufficient to meet the enormous demand of agricultural production, thus relying heavily on imports. According to data disclosed in the "Research Report on Fertilizer Utilization Rate of China's Three Major Grain Crops," my country's annual potash fertilizer demand ranges from 12 million to 14.9 million tons, with import dependence consistently remaining at a high level of around 50%. However, it is worth noting that due to the inherent limitations of soil's ability to absorb and retain potash, excessive application of potash fertilizer not only disrupts the balance of soil nutrient supply, resulting in the needless waste of potash resources, but also, if continued to be applied in excessive amounts of fast-acting potash, in addition to resource waste, is highly likely to induce a series of environmental problems such as soil salinization and water eutrophication.

[0004] To effectively safeguard food security and maintain ecological stability, improving fertilizer utilization efficiency and vigorously promoting slow / controlled-release fertilizers have become urgent tasks in the agricultural sector. In 2015, the "Zero Growth Action Plan for Fertilizer Use" was launched, and in 2022, the "Action Plan for Fertilizer Reduction by 2025" was further formulated, explicitly proposing to promote a steady decline in fertilizer use for crops while continuously improving fertilizer utilization efficiency. Slow / controlled-release fertilizers, with their outstanding advantages of effectively reducing fertilizer loss, mitigating environmental pollution, and significantly improving crop yield and quality, have become a hot research focus in the global agricultural research field. Currently, slow-release potassium fertilizer technology encompasses various types, including coated slow-release potassium fertilizers, zeolite-based slow-release potassium fertilizers, and bentonite-carrier slow-release potassium fertilizers. However, it is undeniable that these existing technologies still face many challenges that urgently need to be overcome. Regarding synthetic material coated potassium fertilizer technology, it faces the dilemma of high cost, and some petrochemical-based coating materials, due to their difficulty in biodegradation, are highly likely to cause long-term potential harm to the ecological environment. Furthermore, traditional potash fertilizer raw materials (such as potassium chloride and potassium sulfate) are mostly irregular particles or flaky crystals with a wide particle size distribution, often greater than 100 μm. Their rough surfaces and sharp edges make them prone to uneven agglomeration during direct granulation due to high inter-particle friction and poor flowability. This results in porous or unevenly textured particles with low sphericity. Direct coating also leads to uneven film distribution and poor slow-release effect. While zeolite / bentonite-based potash fertilizers can achieve slow-release effects by adsorbing potassium ions using the properties of their layered clay minerals, they are limited by their overall adsorption capacity and struggle to precisely control the potassium ion release rate under different soil textures and climatic conditions. Therefore, given the current situation, there is an urgent need to develop an innovative slow-release potash fertilizer product to overcome existing technological bottlenecks and help achieve the goals of high-efficiency and environmentally friendly agricultural production. Summary of the Invention

[0005] In view of this, the purpose of this application is to provide a slow-release potassium fertilizer with controlled-release function and soil improvement function, and a method for preparing the same, to solve the problems of unstable release rate and short service life of existing slow-release potassium fertilizers.

[0006] To achieve the above technical objectives, this application provides a slow-release potassium fertilizer with controlled-release and soil-improving functions, comprising the following components by mass percentage:

[0007] Isocyanates 1-6%;

[0008] Bio-based polyols 1-6%;

[0009] Adhesive 0.1~5%;

[0010] Sealant 0.1~1%;

[0011] The remainder is a mixture of potassium fertilizers;

[0012] The potassium fertilizer mixture consists of ultrafine mineral particles of 150-500 mesh and potassium fertilizer; the ultrafine mineral particles account for 5-50% of the total mass of the potassium fertilizer mixture, and the potassium fertilizer accounts for 50-95% of the total mass of the potassium fertilizer mixture, and the ultrafine mineral particles are coal-based minerals (SRM).

[0013] The sum of the mass percentages of isocyanates and bio-based polyols is less than or equal to 8%.

[0014] Furthermore, it also includes a catalyst and / or a crosslinking agent, wherein the mass percentage of the catalyst and / or crosslinking agent is 0.1 to 0.5%.

[0015] Furthermore, the isocyanate includes one or more of IPDI, HDI, HMDI, TDI, and MDI;

[0016] Bio-based polyols include one or more of castor oil-based polyols, soybean oil-based polyols, palm oil-based polyols, cellulose-based polyols, and sucrose-based polyols.

[0017] Furthermore, the isocyanate and bio-based polyol are PMDI and castor oil-based polyol, respectively, and the mass ratio of PMDI to castor oil-based polyol is 5:6.

[0018] Furthermore, the isocyanate and bio-based polyol are HDI and soybean oil-based polyol, respectively, and the mass ratio of HDI to soybean oil-based polyol is 2:5.

[0019] Furthermore, the potassium fertilizer includes one or more of potassium sulfate, potassium chloride, potassium nitrate, potassium dihydrogen phosphate, potassium humate, and potassium fulvate; the binder includes one or more of CMC, PVA, PAA, starch, humic acid, and sodium stearate.

[0020] Furthermore, the catalyst includes one or more of DBTDL, TEA, and DMCHA; the crosslinking agent includes one or more of TMP, ADH, DAAM, TBC, DOTP, glycerol, epoxidized soybean oil, and pentaerythritol glycerol; and the blocking agent includes one or more of phenol, p-nitrophenol, caprolactam, paraffin wax, microcrystalline wax, sulfonated paraffin wax, terpene resin, and polyethylene wax.

[0021] This application provides a method for preparing a slow-release potassium fertilizer with controlled-release and soil-improving functions, characterized in that...

[0022] Step S1, preparing potassium fertilizer mixture: Take ultrafine mineral particles and mix them evenly with potassium fertilizer to obtain potassium fertilizer mixture;

[0023] Step S2, preparing potassium fertilizer granules: Place the potassium fertilizer mixture in a granulator, start the granulator, and then slowly add a binder until the potassium fertilizer mixture forms granular potassium fertilizer. Dry the granular potassium fertilizer to obtain potassium fertilizer granules.

[0024] Step S3, Coating: Transfer the potassium fertilizer granules into the drum, set the drum speed, and heat the drum to a temperature of 60~80 ℃. Then slowly add the prepolymer coating liquid and mix it with the potassium fertilizer granules. After the prepolymer coating liquid is added, add the sealing agent within a preset time after the prepolymer coating liquid is added. Continue to run the drum until the coating liquid is solidified to obtain pre-coated potassium fertilizer.

[0025] Step S4, multiple coating: Take the pre-coated potassium fertilizer and repeat step S3 multiple times to obtain mineral blend coated potassium fertilizer.

[0026] This application provides a core-shell structure for a slow-release potassium fertilizer, comprising a core and a multilayer coating covering the surface of the core; the core is prepared by mixing ultrafine mineral particles, potassium fertilizer, and a binder; the coating is obtained by coating and curing the core surface with a prepolymer coating liquid formed by mixing isocyanate and bio-based polyol.

[0027] This application provides the application of a slow-release potassium fertilizer with controlled-release and soil-improving functions in crops, including cash crops or food crops.

[0028] In summary, this application provides a slow-release potassium fertilizer with controlled-release and soil-improving functions, and its preparation method. This application blends powdered potassium fertilizer with ultrafine mineral particles and binds them together using a binder to form potassium fertilizer particles with good sphericity. Simultaneously, the potassium fertilizer particles are coated multiple times with a prepolymer coating solution formed by a specific isocyanate and biopolyol. The resulting blended coated potassium fertilizer exhibits excellent slow-release characteristics and an ultra-long nutrient slow-release period, enabling a stable and continuous supply of potassium to crops throughout their growth stages. Furthermore, by introducing ultrafine mineral particles (SRM) into the blend with powdered potassium fertilizer, this application significantly improves the sphericity of the potassium fertilizer particles, making their surface more uniform and smooth, thus providing an ideal substrate for subsequent coating processes. This improvement not only solves the problem of unstable slow-release performance caused by irregular particle size in traditional potash fertilizers, but also reduces the amount of binder used, which is in line with the policy orientation of fertilizer reduction and green manufacturing. In addition, the slow-release potash fertilizer provided by this application also exhibits excellent degradation performance. Compared with the defects of traditional potash fertilizers, which are prone to residues and accumulation in the soil and cause pollution to the ecological environment, the coating provided by this application can achieve rapid degradation and transformation at a relatively high rate after completing its fertilization mission, based on the soil microbial ecology and natural environmental conditions, which greatly reduces the negative impact of residual coatings on the environment.

[0029] Compared with existing technologies, this application overcomes the limitations of traditional slow-release potassium fertilizers, such as short release life and uneven nutrient supply, by introducing a blending strategy of powdered potassium fertilizer with ultrafine mineral particles and an optimized combination of specific isocyanates and biopolyols. It significantly extends the effective duration of slow-release potassium fertilizer, providing solid and reliable nutrient support for crops throughout their growth and development process, and powerfully promoting agricultural production towards a green, efficient, and sustainable direction. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 This is a schematic diagram of the structure of a mineral blend coated potassium fertilizer provided in an embodiment of this application;

[0032] Figure 2 The images show the release effect of slow-release potassium fertilizer at different time periods, which are provided for the embodiments and comparative examples of this application. Detailed Implementation

[0033] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. Based on the embodiments in this application specification, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection claimed in this application.

[0034] The raw materials used in this invention are not particularly restricted in terms of their source; they can be purchased from the market or prepared using conventional methods known to those skilled in the art.

[0035] This application provides a slow-release potassium fertilizer with controlled-release and soil-improving functions, comprising the following components by mass percentage:

[0036] Isocyanates 1-6%;

[0037] Bio-based polyols 1-6%;

[0038] Adhesive 0.1~5%;

[0039] Sealant 0.1~1%;

[0040] The remainder is a mixture of potassium fertilizers;

[0041] The potassium fertilizer mixture consists of ultrafine mineral particles of 150-500 mesh and potassium fertilizer; the ultrafine mineral particles account for 5-50% of the total mass of the potassium fertilizer mixture, and the potassium fertilizer accounts for 50-95% of the total mass of the potassium fertilizer mixture, and the ultrafine mineral particles are ultrafine coal-based minerals (SRM).

[0042] The sum of the mass percentages of isocyanates and bio-based polyols is less than or equal to 8%.

[0043] It should be noted that the ultrafine mineral particles are ultrafine coal-based minerals, and some minerals in SRM possess a certain degree of adhesion. Especially in high-humidity environments, this adhesion can significantly enhance the binding effect of SRM with powdered potassium fertilizer. Furthermore, the processed ultrafine mineral particles have a large specific surface area and surface energy. These characteristics enhance the physical adsorption force between particles, acting as a bridge between them, thus making the potassium fertilizer more stable after molding. The particle size range of SRM (150~500 mesh, corresponding to 25~100 μm) can form a gradient distribution with potassium fertilizer powder, effectively filling the gaps between particles. Through physical filling and surface modification, SRM can reduce the friction coefficient between particles, promoting particle rolling and plastic deformation during granulation, thereby forming particles with smoother surfaces and higher sphericity. After hydrocyclone separation, the 150~500 mesh SRM particles are rich in layered silicate minerals such as kaolinite and illite. The rigid mineral framework of these minerals effectively inhibits shrinkage and deformation of particles during granulation and drying, reduces crack formation, and maintains the integrity of the spherical structure. Simultaneously, the ultrafine mineral particles facilitate the entry of potassium ions into the interlayer spaces of the mineral lamellae, where they are firmly adsorbed. Specifically, kaolinite, with its negatively charged surface, can adsorb positively charged potassium ions through electrostatic attraction, exhibiting uniform adsorption site distribution and high adsorption stability. Illite, with its overlapping crystal layers, forms closed pores capable of adsorbing and fixing large amounts of potassium ions. Furthermore, its large specific surface area and lattice structure provide more adsorption sites, resulting in high adsorption capacity and exchange efficiency for potassium ions. The synergistic effect of kaolinite providing stable surface adsorption and illite providing large specific surface area and high-capacity lattice adsorption enables SRM micro-mineral powder to adsorb and convert large amounts of readily available potassium in the soil, improving the availability of potassium ions and thus enhancing the utilization rate of potassium fertilizer.

[0044] In some embodiments, a catalyst and / or crosslinking agent are further included, wherein the mass percentage of the catalyst and / or crosslinking agent is 0.1 to 0.5%.

[0045] In some embodiments, the isocyanate includes one or more of isophorone diisocyanate (IPDI), hexamethylene diisocyanate (HDI), dicyclohexylmethane diisocyanate (HMDI), toluene diisocyanate (TDI), and diphenylmethane diisocyanate (MDI); the bio-based polyol includes one or more of castor oil-based polyol, soybean oil-based polyol, palm oil-based polyol, cellulose-based polyol, and sucrose-based polyol.

[0046] Preferably, the isocyanate and the bio-based polyol are PMDI and castor oil-based polyol, respectively, and the mass ratio of PMDI to castor oil-based polyol is 5:6.

[0047] Preferably, the isocyanate and the bio-based polyol are HDI and soybean oil-based polyol, respectively, and the mass ratio of HDI to soybean oil-based polyol is 2:5.

[0048] In some embodiments, the potassium fertilizer includes one or more of potassium sulfate, potassium chloride, potassium nitrate, potassium dihydrogen phosphate, potassium humate, and potassium fulvate.

[0049] In some embodiments, the binder includes one or more of carboxymethyl cellulose (CMC), polyacryl alcohol (PVA), sodium polyacrylate (PAA), starch, humic acid, and sodium stearate.

[0050] In some embodiments, the catalyst includes one or more of dibutyltin dilaurate (DBTDL), triethanolamine (TEA), and N,N-dimethylcyclohexylamine (DMCHA); the crosslinking agent includes one or more of trimethylolpropane (TMP), pentaerythritol glycerol, adipate dihydrazide (ADH), diacetone acrylamide (DAAM), glycerol, epoxidized soybean oil, tributyl citrate (TBC), and diesteryl terephthalate (DOTP).

[0051] In some embodiments, the sealing agent includes one or more of phenol, p-nitrophenol, caprolactam, paraffin, microcrystalline wax, sulfonated paraffin, terpene resin, and polyethylene wax.

[0052] This application provides a method for preparing a slow-release potassium fertilizer with controlled-release and soil-improving functions, characterized in that...

[0053] Step S1, Preparation of potassium fertilizer mixture: Take ultrafine mineral particles and mix them evenly with potassium fertilizer to obtain potassium fertilizer mixture; Prepolymer coating solution: Isocyanate and bio-based polyol are mixed to obtain prepolymer coating solution;

[0054] Step S2, preparing potassium fertilizer granules: Place the potassium fertilizer mixture in a granulator, start the granulator, and then slowly add a binder until the potassium fertilizer mixture forms granular potassium fertilizer. Dry the granular potassium fertilizer to obtain potassium fertilizer granules; without the action of a binder, start the granulator and spray a small amount of water to slightly moisten the system. The potassium fertilizer mixture can also form granular potassium fertilizer with better sphericity through the interaction force between ultrafine mineral particles.

[0055] Step S3, Coating: Transfer the potassium fertilizer granules into the drum, set the drum speed, and heat the drum to a temperature of 60~80 ℃. Then slowly add the prepolymer coating liquid and mix it with the potassium fertilizer granules. After the prepolymer coating liquid is added, add the sealing agent within a preset time after the prepolymer coating liquid is added. Continue to run the drum until the coating liquid is solidified to obtain pre-coated potassium fertilizer.

[0056] Step S4, multiple coating: Take the pre-coated potassium fertilizer and repeat step S3 multiple times to obtain mineral blend coated potassium fertilizer.

[0057] Specifically, the preset duration is 3 to 5 minutes.

[0058] It should be noted that the structure of mineral blend coated potassium fertilizer is as follows: Figure 1 As shown, the internal core consists of spherical particles (potassium fertilizer particles) with a particle size of 2-4 mm, formed by uniformly mixing ultrafine coal-based mineral powder and potassium fertilizer powder and bonding them together with a binder. The outer coating is a dense polyurethane membrane material formed from isocyanate and bio-based polyol.

[0059] This application provides a core-shell structure for a slow-release potassium fertilizer, comprising a core and a multilayer coating covering the surface of the core; the core is prepared by mixing ultrafine mineral particles, potassium fertilizer, and a binder; the coating is obtained by coating and curing the core surface with a prepolymer coating liquid formed by mixing isocyanate and bio-based polyol.

[0060] This application provides an example of the application of a slow-release potassium fertilizer with controlled-release and soil-improving functions in crops, including cash crops or food crops.

[0061] It should be noted that all of the above-mentioned crops have a significant demand for potassium throughout their entire growth stage. Applying the slow-release potassium fertilizer provided in this application to the planting stage of these crops can provide potassium fertilizer to the crops for a long period of time and stably, thereby increasing crop yield.

[0062] The applicant further provides the following specific embodiments to describe the present invention. It should be noted that these embodiments are merely descriptive and do not limit the present invention in any way.

[0063] Example 1

[0064] This application provides a method for preparing a slow-release potassium fertilizer with controlled-release and soil-improving functions, comprising the following steps:

[0065] Step S1, Raw material preparation:

[0066] Preparation of 150-500 mesh ultrafine mineral particles: Ultrafine mineral particles (SRM) were obtained using micromineral separation technology, and ultrafine mineral particles with a particle size of 150-500 mesh were screened using a hydrocyclone for later use.

[0067] Preparation of adhesive: Take 5 g of corn starch and disperse it in 40 g of water and stir evenly. Then add 1.5 g of PVA, continue stirring and heat to 60~80 ℃ to form an adhesive for later use.

[0068] Preparation of prepolymer coating solution: Mix TDI and palm oil-based polyol at a mass ratio of 2:3 until homogeneous;

[0069] Step S2, preparing potassium fertilizer mixture: Take 200 g of 150~500 mesh ultrafine mineral particles prepared in step S1 and mix them with 300 g of powdered potassium chloride for 15 min to obtain potassium fertilizer mixture.

[0070] Step S3, preparing potassium fertilizer granules: Place the potassium fertilizer mixture in a disc granulator, adjust the tilt angle of the disc to 45° and the rotation speed to 25 r / min, then slowly add the binder until granular potassium fertilizer with a particle size of 2~4 mm is formed. Dry the granular potassium fertilizer to obtain potassium fertilizer granules.

[0071] Step S4, Coating: Transfer the potassium fertilizer granules to a drum, set the drum speed to 25 r / min, and heat it to keep the internal temperature of the drum at 60 ℃. Then slowly add 5 g of prepolymer coating liquid, and stir for 3 min after the prepolymer coating liquid is added. Then add liquid paraffin as a sealing agent and continue stirring for 10~15 min until the coating liquid solidifies to obtain pre-coated potassium fertilizer.

[0072] Step S5, multiple coating: Take the pre-coated potassium fertilizer and repeat step S4 twice to obtain mineral blend coated potassium fertilizer. During the multiple coating process, the total amount of liquid paraffin added is 0.5 g.

[0073] Example 2

[0074] This application provides a method for preparing a slow-release potassium fertilizer with controlled-release and soil-improving functions, comprising the following steps:

[0075] Step S1, Raw material preparation:

[0076] Preparation of 150-500 mesh ultrafine mineral particles: Ultrafine mineral particles (SRM) were obtained using micromineral separation technology, and ultrafine mineral particles with a particle size of 150-500 mesh were screened using a hydrocyclone for later use.

[0077] Preparation of adhesive: Disperse 5 g of corn starch in 40 g of water and stir evenly. Then add 1.5 g of PVA and 0.1 g of glycerin, continue stirring and heat to 60~80 ℃ to form an adhesive for later use.

[0078] Preparation of prepolymer coating solution: Mix MDI and castor oil-based polyol at a mass ratio of 1:2 until homogeneous;

[0079] Step S2, Mixing potassium fertilizer: Take 200 g of 150-500 mesh ultrafine mineral particles prepared in step S1 and mix them with 300 g of powdered potassium chloride for 15 min to obtain a potassium fertilizer mixture.

[0080] Step S3, preparing potassium fertilizer granules: Place the potassium fertilizer mixture in a disc granulator, adjust the tilt angle of the disc to 45° and the rotation speed to 25 r / min, then slowly add the binder until granular potassium fertilizer with a particle size of 2~4 mm is formed. Dry the granular potassium fertilizer to obtain potassium fertilizer granules.

[0081] Step S4, Coating: Transfer the potassium fertilizer granules to a drum, set the drum speed to 25 r / min, and heat it to keep the internal temperature of the drum at 70 ℃. Then slowly add 5 g of prepolymer coating liquid and 0.1 g of DBTDL. After the prepolymer coating liquid is added, stir for 3 min and then add molten flake paraffin as a sealing agent. Continue stirring for 10~15 min until the coating liquid solidifies to obtain pre-coated potassium fertilizer.

[0082] Step S5 involves multiple coating processes. The pre-coated potassium fertilizer is then used in step S4 three times to obtain a mineral blend coated potassium fertilizer. During these multiple coating processes, the total amount of molten flake paraffin added is 0.5 g.

[0083] Example 3

[0084] This application provides a method for preparing a slow-release potassium fertilizer with controlled-release and soil-improving functions, comprising the following steps:

[0085] Step S1, Raw material preparation:

[0086] Preparation of 150-500 mesh ultrafine mineral particles: Ultrafine mineral particles (SRM) were obtained using micromineral separation technology, and ultrafine mineral particles with a particle size of 150-500 mesh were screened using a hydrocyclone for later use.

[0087] Preparation of adhesive: Disperse 8 g of CMC in 80 g of water and stir evenly. Then add 1.5 g of PVA, continue stirring and heat to 70 °C to form an adhesive for later use.

[0088] Preparation of prepolymer coating solution: Mix HDI and soybean oil-based polyol at a mass ratio of 2:5 until homogeneous;

[0089] Step S2, Mixing potassium fertilizer: Take 200 g of 150-500 mesh ultrafine mineral particles prepared in step S1 and mix them with 300 g of powdered potassium sulfate for 15 min to obtain a potassium fertilizer mixture.

[0090] Step S3, preparing potassium fertilizer granules: Place the potassium fertilizer mixture in a disc granulator, adjust the tilt angle of the disc to 45° and the rotation speed to 25 r / min, then slowly add the binder until granular potassium fertilizer with a particle size of 2~4 mm is formed. Dry the granular potassium fertilizer to obtain potassium fertilizer granules.

[0091] Step S4, Coating: Transfer the potassium fertilizer granules to a drum, set the drum speed to 25 r / min, and heat the drum to keep the internal temperature at 70 ℃. Then slowly add 5 g of prepolymer coating liquid, and stir for 3 min after the prepolymer coating liquid is added. Then add molten microcrystalline wax as a sealing agent and continue stirring for 10~15 min until the coating liquid solidifies to obtain pre-coated potassium fertilizer.

[0092] Step S5, multiple coating: Repeat step S4 four times with the pre-coated potassium fertilizer to obtain mineral blend coated potassium fertilizer. During the multiple coating processes, the total amount of molten microcrystalline wax added is 0.3 g.

[0093] Example 4

[0094] Step S1, Raw material preparation:

[0095] Preparation of 150-500 mesh ultrafine mineral particles: Ultrafine mineral particles (SRM) were obtained using micromineral separation technology, and ultrafine mineral particles with a particle size of 150-500 mesh were screened using a hydrocyclone for later use.

[0096] Preparation of adhesive: Disperse 5 g of PAA in 50 g of water and stir evenly. Continue stirring and heat to 60~80℃ to form an adhesive for later use.

[0097] Preparation of prepolymer coating solution: Mix PMDI and castor oil-based polyol at a mass ratio of 1:1.2 until homogeneous;

[0098] Step S2, Mixing potassium fertilizer: Take 200 g of 150-500 mesh ultrafine mineral particles prepared in step S1 and mix them with 300 g of powdered potassium sulfate for 15 min to obtain a potassium fertilizer mixture.

[0099] Step S3, preparing potassium fertilizer granules: Place the potassium fertilizer mixture in a disc granulator, adjust the tilt angle of the disc to 45° and the rotation speed to 25 r / min, then slowly add the binder until granular potassium fertilizer with a particle size of 2~4 mm is formed. Dry the granular potassium fertilizer to obtain potassium fertilizer granules.

[0100] Step S4, Coating: Transfer the potassium fertilizer granules to a drum, set the drum speed to 25 r / min, and heat it to keep the internal temperature of the drum at 80 ℃. Then slowly add 5 g of prepolymer coating liquid, and stir for 3 min after the prepolymer coating liquid is added. Then add molten polyethylene wax as a sealing agent and continue stirring for 10~15 min until the coating liquid solidifies to obtain pre-coated potassium fertilizer.

[0101] Step S5, multiple coating: Repeat step S4 five times with the pre-coated potassium fertilizer to obtain mineral blend coated potassium fertilizer. During the multiple coating processes, the total amount of molten polyethylene wax added is 0.3 g.

[0102] Example 5

[0103] Step S1, Raw material preparation:

[0104] Preparation of 150-500 mesh ultrafine mineral particles: Ultrafine mineral particles (SRM) were obtained using micromineral separation technology, and ultrafine mineral particles with a particle size of 150-500 mesh were screened using a hydrocyclone for later use.

[0105] Preparation of adhesive: Disperse 5 g of PAA in 50 g of water and stir evenly. Then add 1.5 g of PVA, continue stirring and heat to 80 ℃ to form an adhesive for later use.

[0106] Preparation of prepolymer coating solution: Mix PMDI and palm oil-based polyol at a mass ratio of 1:2.5 until homogeneous;

[0107] Step S2, Mixing potassium fertilizer: Take 200 g of 150-500 mesh ultrafine mineral particles prepared in step S1 and mix them with 300 g of powdered potassium sulfate for 15 min to obtain a potassium fertilizer mixture.

[0108] Step S3, preparing potassium fertilizer granules: Place the potassium fertilizer mixture in a disc granulator, adjust the tilt angle of the disc to 45° and the rotation speed to 25 r / min, then slowly add the binder until granular potassium fertilizer with a particle size of 2~4 mm is formed. Dry the granular potassium fertilizer to obtain potassium fertilizer granules.

[0109] Step S4, Coating: Transfer the potassium fertilizer granules to a drum, set the drum speed to 25 r / min, and heat it to keep the internal temperature of the drum at 80 ℃. Then slowly add 5 g of prepolymer coating liquid, and stir for 3 min after the prepolymer coating liquid is added. Then add molten polyethylene wax as a sealing agent and continue stirring for 10~15 min until the coating liquid solidifies to obtain pre-coated potassium fertilizer.

[0110] Step S5, multiple coating: Repeat step S4 five times with the pre-coated potassium fertilizer to obtain mineral blend coated potassium fertilizer. During the multiple coating processes, the total amount of molten polyethylene wax added is 0.3 g.

[0111] Comparative Example 1

[0112] This application provides a method for preparing a slow-release potassium fertilizer with controlled-release and soil-improving functions, comprising the following steps:

[0113] Step S1, Raw material preparation:

[0114] Preparation of adhesive: Disperse 5 g of corn starch in 40 g of water, stir evenly, and heat to 60~80 ℃ to form an adhesive for later use;

[0115] Step S2, preparing potassium fertilizer granules: Place 500g of potassium chloride in a disc granulator, adjust the tilt angle of the disc to 45° and the rotation speed to 25 r / min, then slowly add the binder until the potassium chloride forms granules with a particle size of 2~4 mm. Dry the granules to obtain potassium fertilizer granules.

[0116] Comparative Example 2

[0117] This application provides a method for preparing a slow-release potassium fertilizer with controlled-release and soil-improving functions, comprising the following steps:

[0118] Step S1, Raw material preparation:

[0119] Preparation of 150-500 mesh ultrafine mineral particles: Ultrafine mineral particles (SRM) were obtained using micromineral separation technology, and ultrafine mineral particles with a particle size of 150-500 mesh were screened using a hydrocyclone for later use.

[0120] Preparation of adhesive: Disperse 5 g of corn starch in 40 g of water, stir evenly, and heat to 60~80 ℃ to form an adhesive for later use;

[0121] Preparation of prepolymer coating solution: Mix hexamethylene diisocyanate (HDI) and soybean oil-based polyol at a mass ratio of 1:3 until homogeneous;

[0122] Step S2, Coating: Take the potassium fertilizer granules prepared in Comparative Example 1 and perform a coating operation. Transfer the potassium fertilizer granules to a drum, set the drum speed to 25 r / min, and heat it to keep the internal temperature of the drum at 60 ℃. Then slowly add 5 g of prepolymer coating liquid. When the prepolymer coating liquid is evenly distributed on the surface of powdered potassium chloride, add 50 g of SRM micro-mineral powder, continue stirring for 3 min, and then add molten polyethylene wax as a sealing agent. Then continue stirring for 10~15 min until the coating liquid solidifies to obtain pre-coated potassium fertilizer.

[0123] Step S3, multiple coating: Take the pre-coated potassium fertilizer and repeat step S2 once, then gradually add 5g of prepolymer coating liquid and continue stirring. After 3 minutes, add molten polyethylene wax as a sealing agent, and then continue to rotate and stir for 10-15 minutes until the coating liquid solidifies to obtain mineral-coated potassium fertilizer. The total amount of liquid paraffin added is 1.0 g.

[0124] Comparative Example 3

[0125] This application provides a method for preparing a slow-release potassium fertilizer with controlled-release function, comprising the following steps:

[0126] Step S1, Raw material preparation:

[0127] Preparation of adhesive: Take 5 g of corn starch and disperse it in 40 g of water and stir evenly. Then add 1.5 g of PVA, continue stirring and heat to 60~80 ℃ to form an adhesive for later use.

[0128] Preparation of prepolymer coating solution: Mix TDI and palm oil-based polyol at a mass ratio of 2:3 until homogeneous;

[0129] Step S2, preparing potassium fertilizer granules: Place 500g of potassium chloride powder in a disc granulator, adjust the tilt angle of the disc to 45° and the rotation speed to 25 r / min, then slowly add binder until granular potassium fertilizer with a particle size of 2~4 mm is formed. Dry the granular potassium fertilizer to obtain potassium fertilizer granules.

[0130] Step S3, Coating: Transfer the potassium fertilizer granules to a drum, set the drum speed to 25 r / min, and heat it to keep the internal temperature of the drum at 60 ℃. Then slowly add 5 g of prepolymer coating liquid, and stir for 3 min after the prepolymer coating liquid is added. Then add liquid paraffin as a sealing agent and continue stirring for 10~15 min until the coating liquid solidifies to obtain pre-coated potassium fertilizer.

[0131] Step S4, multiple coating: Take the pre-coated potassium fertilizer and repeat step S3 twice to obtain coated potassium fertilizer. During the multiple coating processes, the total amount of liquid paraffin added is 0.5 g.

[0132] The differences in the preparation methods provided in Examples 1-5 and Comparative Examples 1-3 are shown in Table 1.

[0133] Table 1. Differences in parameter settings between the examples and comparative examples

[0134]

[0135] Note: The core in Table 1 is potassium fertilizer granules.

[0136] Test 1: Slow-release potassium fertilizer slow-release life test

[0137] Nutrient release lifetime of the potassium fertilizer granules, mineral-coated potassium fertilizer, and mineral blend-coated potassium fertilizer prepared in the above embodiments and comparative examples was determined according to the national standard GB / T 22923. The nutrient release lifetime was recorded as the time required for 80% of the total nutrients to be released. The experimental results are shown in Table 2, and the nutrient release curves are shown in Table 2. Figure 2 As shown in the figure, coated potassium fertilizer 1 is the slow-release potassium fertilizer prepared in Comparative Example 3; mineral coated potassium fertilizer 1 is the slow-release potassium fertilizer prepared in Comparative Example 2; mineral blend coated potassium fertilizers 1-5 are the slow-release potassium fertilizers prepared in Examples 1-5 respectively.

[0138] Table 2. Comparison of the slow-release effects of the slow-release potassium fertilizers prepared in the examples and comparative examples.

[0139]

[0140] Experiments were conducted to investigate the slow-release characteristics of potassium fertilizer under different preparation processes, and the results are shown in Table 2. Comparative Example 1 involved potassium fertilizer granules simply bonded together with powdered potassium chloride and a binder. Comparative Example 2, based on Comparative Example 1, used a prepolymer coating liquid and ultrafine mineral particles to layer and coat the potassium fertilizer granules, thus forming a coated potassium fertilizer. However, the test data showed that the nutrient slow-release lifespan of Comparative Examples 1 and 2 was significantly different from that of the mineral-blended coated potassium fertilizer formed by blending powdered potassium fertilizer with ultrafine mineral particles and then coating it in the examples. The slow-release lifespan of the potassium fertilizer provided by the comparative examples was much shorter than that of the examples. This indicates that the preparation method of first blending potassium fertilizer with ultrafine mineral particles and then coating them can effectively extend the nutrient slow-release time of the potassium fertilizer, providing a strong guarantee for continuous and stable fertilization throughout the crop growth cycle.

[0141] Further comparative analysis of Examples 1-5 presented in the table reveals that Examples 3 and 4 are particularly effective in improving sustained-release performance. Specifically, a detailed comparison of the effects of Examples 3 and 5 shows that Example 3 only underwent four repeated coating operations, while Example 5 underwent five. Logically, in coating processes, an increase in the number of coating operations should generally be positively correlated with the enhancement of sustained-release function; that is, more coating operations theoretically help to slow down the nutrient release rate and enhance sustained-release performance. However, actual test results show that the sustained-release lifespan of Example 3 is stronger than that of Example 5. This indicates that the coating structure formed by the prepolymer coating liquid prepared from HDI and soybean oil-based polyols used in Example 3 has superior sustained-release performance compared to the coating constructed in Example 5. This finding fully demonstrates that the combination of HDI and soybean oil-based polyols selected in Example 3 has unique chemical properties, and the two can achieve a more subtle synergistic effect, thereby greatly extending the sustained-release lifespan of the potassium fertilizer in Example 3.

[0142] Also noteworthy is Example 4, which uses PMDI and castor oil-based polyols as prepolymer coating solutions to prepare mineral blend coated potassium fertilizer. Experimental results show that the slow-release lifespan of this example can reach up to 98 days, a significant advantage compared to Examples 3 and 5. Table 1 shows that the key difference in preparation parameters between Examples 5 and 4 lies mainly in the composition of the prepolymer coating solution. Example 5 uses a mixture of PMDI and palm oil to prepare the prepolymer coating solution, meaning the types of bio-based polyols used are completely different. This comparison clearly demonstrates that the combination of castor oil-based polyols and PMDI selected in Example 4 possesses unique chemical activity, and their interaction achieves a more ideal synergistic effect, resulting in a significant increase in the slow-release lifespan of the potassium fertilizer prepared in Example 4.

[0143] Test 2: Sphericity test of uncoated potassium fertilizer

[0144] The effect of adding ultrafine coal-based mineral spheric reticulum (SRM) during the granulation of powdered potassium fertilizer was evaluated. The control group used pure potassium fertilizer granules prepared according to Comparative Example 1, while the experimental group used mineral blend granules prepared according to the process of Comparative Example 1, except that 500 g of potassium chloride powder was replaced with 200 g of 150-500 mesh SRM blended with 300 g of potassium chloride powder. Sphericity was tested on both groups of granules using the image method specified in standard T / CCEMA 0001-2020. Particles with a diameter range of 3-4 mm were screened using a sieve machine in both the experimental and control groups, and 100 particles were randomly selected for testing. The test was repeated three times, and the particles were shaken and redispersed after each test to ensure images were obtained from different angles. Finally, the projected roundness index of the particles was statistically analyzed, and the results are shown in Table 3.

[0145] Table 3. Comparison of Particle Sphericity

[0146]

[0147] Table 3 shows that the average roundness index of the mineral blended potassium fertilizer granules was 0.862±0.012, significantly higher than that of pure potassium fertilizer granules (0.723±0.025). This indicates that the mineral blended potassium fertilizer granules prepared by adding 150-500 mesh SRM have better sphericity. Observation of Example 1 and Comparative Example 3 reveals that although both used the same coating process, the nutrient release life of the slow-release fertilizer prepared in Example 1 was significantly longer than that in Comparative Example 3. Example 1 added SRM during the preparation of potassium fertilizer granules, improving the sphericity of the granules and thus providing a more ideal substrate for subsequent coating. From the perspective of the coating process, the uniform surface curvature of spherical granules allows the coating solution to spread more evenly on the granule surface, forming a film of consistent thickness and avoiding localized excessively thick or thin films. Furthermore, granules with higher sphericity experience more uniform stress during the drum coating process, reducing collisions and friction between granules and lowering the risk of film damage. These factors work together to give mineral blend potassium fertilizer particles with higher sphericity a longer slow-release lifespan after coating.

[0148] Test 3: Fertilizer Efficiency Test

[0149] This study validated the efficacy of different potassium fertilizers using a tomato pot experiment. The test soil was taken from farmland in Tengzhou, Shandong Province, with the following basic physicochemical properties: pH 6.33 and electrical conductivity 243.1 µS / cm. Before the experiment, the soil was air-dried and then passed through a 2 mm sieve to ensure uniformity. Cherry tomato was selected as the test plant variety. The standardized procedure of watering → sowing → covering with soil was strictly followed during the cherry tomato sowing process. Thinning was carried out 15 days after sowing, with one seedling precisely planted in each pot. To ensure consistency in initial plant growth conditions, seedlings with true leaves and good growth were selected for subsequent fertilizer efficacy testing. The seedlings with true leaves and good growth were placed in a greenhouse for cultivation. The greenhouse temperature was precisely controlled at 25 ℃, ensuring 12 hours of light per day, and 100 mL of water was applied every 72 hours to minimize the interference of environmental factors on the experimental results. During the cultivation process, selected seedlings were uniformly fertilized with nitrogen and phosphorus base fertilizer as the basic nutrient supply. Five experimental groups were set up, using slow-release potassium fertilizers prepared in Examples 3-4 and Comparative Examples 1-3 as nutrients, respectively. The available potassium content in the potassium fertilizers applied to all experimental groups was the same, and each experimental group had 20 cherry tomato plants as parallel samples. After 120 days of continuous cultivation, the tomato plants were harvested after maturity, and mature plants were selected for the measurement and analysis of various growth indicators. The results of each experimental group were calculated as the average of 20 replicate samples. Detailed data are summarized in Table 4 to facilitate further comparison of the differences in growth performance of cherry tomato plants under different potassium fertilizer treatments, and to accurately evaluate the fertilizer efficiency characteristics of each potassium fertilizer.

[0150] Table 4. Comparison of the fertilizer effects of slow-release potassium fertilizer

[0151]

[0152] Table 4, a comparison of the effects of slow-release potassium fertilizers, shows that different slow-release potassium fertilizers exhibited varying fertilizer efficacy characteristics in tomato pot experiments. Comparative Example 1 consisted of potassium fertilizer granules made from powdered potassium chloride bonded with a binder; Comparative Example 2 was a coated potassium fertilizer formed by layering prepolymer coating liquid and ultrafine mineral particles based on Comparative Example 1; Example 3 was a mineral blend coated potassium fertilizer formed by coating powdered potassium fertilizer with ultrafine mineral particles. The table shows that the mineral blend coated potassium fertilizers, represented by Examples 3 and 4, have greater advantages in plant growth and development compared to Comparative Examples 1 and 2. For key data such as plant height, root length, aboveground dry weight, and underground dry weight, the potassium fertilizers prepared in these examples significantly promote plant growth. For example, the plant height corresponding to Example 3 reached 28.11 cm, the root length was 23.82 cm, the aboveground dry weight was 5.21 g, and the underground dry weight was 0.59 g. Compared with the plant height of 24.21 cm and the root length of 18.32 cm in Comparative Example 1, this clearly shows that Examples 3-4, which repeatedly coated the potassium fertilizer particles formed by blending powdered potassium fertilizer and ultrafine mineral particles, can provide more sufficient nutrients to the plants. This also means that the mineral blended coated potassium fertilizer prepared in Examples 3-4 performs better in nutrient release and improving the plant's absorption and utilization efficiency. In summary, the mineral blended coated potassium fertilizer can effectively control the release rate of potassium ions, allowing potassium fertilizer to be released gradually over a longer period of time. This can not only avoid the salt damage to plant roots caused by high concentrations of potassium ions and improve the plant's absorption efficiency of potassium ions, but also reduce the loss of potassium fertilizer in the soil and significantly reduce the risk of environmental pollution. In addition, after the coating layer degrades naturally in the soil, the released micro-mineral powder can increase the soil porosity and water retention, improve the soil structure, and open up the migration channels of potassium ions in the soil, making it easier for potassium ions to reach the plant roots and further promote plant growth.

[0153] Test 4: Soil degradation rate

[0154] Soil degradation experiments were conducted at 25 ℃ and controlled air humidity at 50%. Polyurethane coatings were prepared using HDI and different polyols; petrochemical-based materials included polypropylene glycol-based polyurethane, and bio-based materials included soybean oil-based polyol and castor oil-based polyol. The raw materials were synthesized into coatings on polytetrafluoroethylene plates using the same process as fertilizer coating. The coatings were then peeled off, and 3 cm × 3 cm samples were cut and weighed. Soil samples from test 2 were placed in leaching containers, and the two prepared coatings were buried 2 cm below the soil surface. 100 mL of water was added to the containers every 72 h. Samples were removed, washed, dried, weighed, and the weight loss rate was calculated every 10 days. The experimental period was 120 days. Three parallel samples were used in each group, and the average value was statistically analyzed. The results are shown in Table 5.

[0155] Table 5. Weight loss rate of polyurethane coatings of different materials

[0156]

[0157] The degradation effect of the coating in soil was analyzed based on the weight loss rate shown in Table 5. The table reveals that polyurethane coatings of different materials exhibit varying degradation rates. Coatings made from bio-based materials (such as soybean oil-based polyol-based polyurethane and castor oil-based polyol-based polyurethane) showed a higher weight loss rate compared to petrochemical-based (polypropylene glycol-based polyurethane) coatings. This indicates that under the current specific soil conditions, coatings constructed from bio-based materials are more susceptible to rapid decomposition and transformation by soil microbial communities and other complex biochemical processes, achieving efficient degradation and reducing the residual time of waste coatings in the soil environment. This fundamentally reduces the potential risk of persistent pollution to the soil ecosystem caused by long-term material retention.

[0158] The above are merely preferred embodiments of this application and are not intended to limit the present invention. Although this application has been described in detail with reference to examples, those skilled in the art can still modify the technical solutions described in the foregoing examples or make equivalent substitutions for some of the technical features. However, any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A slow-release potassium fertilizer with controlled-release and soil-improving functions, characterized in that, The components include the following percentages by mass: Isocyanates 1-6%; Bio-based polyols 1-6%; Adhesive 0.1~5%; Sealant 0.1~1%; The remainder is a mixture of potassium fertilizers; The potassium fertilizer mixture is composed of ultrafine mineral particles of 150-500 mesh and potassium fertilizer; wherein the ultrafine mineral particles account for 5-50% of the total mass of the potassium fertilizer mixture, and the potassium fertilizer accounts for 50-95% of the total mass of the potassium fertilizer mixture, and the ultrafine mineral particles are ultrafine coal-based minerals. The sum of the mass percentages of the isocyanate and the bio-based polyol is less than or equal to 8%.

2. The slow-release potassium fertilizer with controlled-release and soil-improving functions according to claim 1, characterized in that, It also includes a catalyst and / or a crosslinking agent, wherein the mass percentage of the catalyst and / or crosslinking agent is 0.1 to 0.5%.

3. The slow-release potassium fertilizer with controlled-release and soil-improving functions according to claim 1, characterized in that: The isocyanate includes one or more of IPDI, HDI, HMDI, TDI, and MDI; The bio-based polyols include one or more of castor oil-based polyols, soybean oil-based polyols, palm oil-based polyols, cellulose-based polyols, and sucrose-based polyols.

4. The slow-release potassium fertilizer with controlled-release function and soil improvement function according to claim 3, characterized in that: The isocyanate and bio-based polyol are PMDI and castor oil-based polyol, respectively, and the mass ratio of PMDI to castor oil-based polyol is 5:

6.

5. The slow-release potassium fertilizer with controlled-release function and soil improvement function according to claim 3, characterized in that: The isocyanate and bio-based polyol are HDI and soybean oil-based polyol, respectively, and the mass ratio of HDI to soybean oil-based polyol is 2:

5.

6. The slow-release potassium fertilizer with controlled-release function and soil improvement function according to claim 1, characterized in that: The potassium fertilizer includes one or more of potassium sulfate, potassium chloride, potassium nitrate, potassium dihydrogen phosphate, potassium humate, and potassium fulvate. The binder includes one or more of CMC, PVA, PAA, starch, humic acid, and sodium stearate.

7. The slow-release potassium fertilizer with controlled-release function and soil improvement function according to claim 2, characterized in that: The catalyst includes one or more of DBTDL, TEA, and DMCHA; The crosslinking agent includes one or more of TMP, ADH, DAAM, TBC, DOTP, glycerol, epoxidized soybean oil, and pentaerythritol glycerol; The sealing agent includes one or more of phenol, p-nitrophenol, caprolactam, paraffin, microcrystalline wax, sulfonated paraffin, terpene resin, and polyethylene wax.

8. A method for preparing a slow-release potassium fertilizer with controlled-release function and soil improvement function as described in any one of claims 1 to 7, characterized in that: Step S1, preparing potassium fertilizer mixture: Take ultrafine mineral particles and mix them evenly with potassium fertilizer to obtain potassium fertilizer mixture; prepare prepolymer coating solution: mix isocyanate and bio-based polyol to obtain prepolymer coating solution; Step S2, preparing potassium fertilizer granules: Place the potassium fertilizer mixture in a granulator, start the granulator, and then slowly add a binder until the potassium fertilizer mixture forms granular potassium fertilizer. Dry the granular potassium fertilizer to obtain potassium fertilizer granules. Step S3, Coating: Transfer the potassium fertilizer granules into the drum, set the drum speed, and heat the drum to a temperature of 60~80 ℃. Then slowly add the prepolymer coating liquid and mix it with the potassium fertilizer granules. After the prepolymer coating liquid is added, add the sealing agent within a preset time after the prepolymer coating liquid is added. Continue to run the drum until the coating liquid is solidified to obtain pre-coated potassium fertilizer. Step S4, multiple coatings: Take the pre-coated potassium fertilizer and repeat step S4 multiple times to obtain mineral blend coated potassium fertilizer.

9. A core-shell structure for a slow-release potassium fertilizer, characterized in that, It includes a core and a multi-layer coating on the surface of the core; the core is prepared by mixing ultrafine mineral particles, potassium fertilizer and binder; the coating is obtained by coating and curing the core surface with a prepolymer coating liquid formed by mixing isocyanate and bio-based polyol.

10. The application of a slow-release potassium fertilizer with controlled-release and soil-improving functions as described in any one of claims 1 to 7, or a slow-release potassium fertilizer prepared by the method described in claim 8, in crop cultivation, characterized in that, The crops mentioned include cash crops or food crops.

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