Granular magnesium fertilizer and preparation method therefor, blended fertilizer, and nitrogen-magnesium compound fertilizer

Abstract

A granular magnesium fertilizer and a preparation method therefor, a blended fertilizer, and a nitrogen-magnesium compound fertilizer. The preparation method for a granular magnesium fertilizer comprises the following steps: mixing magnesium sulfate monohydrate, light calcined magnesia and a solvent to form a mixed material; and using a double-roller compaction process to carry out compaction granulation on the mixed material.

Description

Granular magnesium fertilizer and preparation method thereof, blended fertilizer and nitrogen-magnesium compound fertilizer

[0001] Related applications

[0002] This application claims priority to Chinese patent application No. 2023115243039, filed on November 15, 2023, entitled “Granular magnesium fertilizer, preparation method thereof, blended fertilizer and nitrogen-magnesium compound fertilizer,” the entire text of which is hereby incorporated by reference. Technical Field

[0003] The present application relates to the technical field of fertilizers, and in particular to a granular magnesium fertilizer and a preparation method thereof, a blended fertilizer, and a nitrogen-magnesium compound fertilizer. Background Art

[0004] Currently, many agricultural fields suffer from severe magnesium deficiency. According to the law of minimum nutrient, one of the three major laws of plant nutrition, if magnesium fertilizers are not effectively applied during fertilization, magnesium becomes a key nutrient in most farmlands, limiting the magnesium supply. Consequently, crop yield and quality are hampered by soil magnesium deficiency. This soil magnesium deficiency and a lack of awareness of magnesium supplementation in agricultural production have resulted in typical magnesium deficiency symptoms in many crops. For example, fruit trees such as citrus and grapes, vegetables such as tomatoes and winter melons, and cash crops such as rapeseed, sugarcane, sweet potatoes, potatoes, sweet corn, and rice all exhibit varying degrees of magnesium deficiency. Consequently, magnesium deficiency in crops has become a limiting nutrient factor for improving crop yield and quality. Furthermore, soil magnesium deficiency can also affect crop absorption and utilization of other nutrients (such as nitrogen, phosphorus, and potassium fertilizers). On the one hand, crop roots are sensitive to magnesium. Magnesium deficiency inhibits root growth and development, reducing nutrient absorption from the soil and from fertilization. On the other hand, magnesium deficiency affects leaf photosynthesis and the transport and conversion of photosynthetic products, leading to reduced crop growth. When magnesium is present, leaf photosynthesis and the transport and conversion of photosynthetic products are enhanced, leading to greater crop growth. The ratio of crop growth to nutrient input can indicate fertilizer utilization efficiency. Therefore, when magnesium is deficient, crop growth decreases even with the same amount of nitrogen, phosphorus, and potassium fertilizer, indicating a low nitrogen, phosphorus, and potassium fertilizer utilization efficiency.

[0005] At present, simplified fertilization is an extremely important demand, and the consumption of compound fertilizers has been increasing year by year. It can be seen that compound fertilizer (blended fertilizer) is one of the important trends in the agricultural market, which also meets the current needs of growers for simplified fertilization. Blended fertilizer is a granular fertilizer made by dry mixing with nitrogen, phosphorus, and potassium as the main nutrients, mixed with other required elements (such as magnesium), and is a type of compound fertilizer (GB / T 21633-2020 blended fertilizer (BB fertilizer)). Among them, the magnesium element that can be mixed in the blended fertilizer must have the following properties at the same time: 1) a high critical relative humidity; 2) a low internal moisture content; 3) difficulty in releasing crystal water.

[0006] However, the current production methods of granular magnesium sulfate are usually disc granulation or drum granulation processes. In the process of producing granular magnesium sulfate by these two methods, water is one of the necessary granulation aids, so the moisture content in the granular magnesium sulfate finally obtained is generally about 3%-5%. When this granular magnesium sulfate containing water is mixed with other granular fertilizers such as nitrogen, phosphorus and potassium fertilizers, urea, etc., the moisture therein will gradually migrate to the surface of the particles and then adhere to other particles, causing the blended fertilizer to agglomerate, thereby causing the blended fertilizer to deteriorate and be unable to be normally circulated and applied. Dry granulation, such as roller granulation, requires the extruded particles to have a "cold flow" characteristic, that is, when high pressure is applied from a certain direction, the crystal lattice of the material allows ions to slide along these lattice layers, that is, the cubic lattice structure of the material needs to have many "layers", and the orientation angles of the ions are the same and the distances between the ions are the same. The crystal structure of magnesium sulfate is an asymmetric monorthic crystal structure, and the orientation angles of its ions are different, which results in very few sliding surfaces between the crystal lattices, causing the magnesium sulfate crystals to be unable to slide to a stable new position. In other words, magnesium sulfate does not have "cold flow" properties and cannot be granulated through the dry roller granulation process.

[0007] Summary of the Invention

[0008] According to various embodiments of the present application, a granular magnesium fertilizer and a preparation method thereof, a blended fertilizer and a nitrogen-magnesium compound fertilizer are provided.

[0009] In a first aspect, the present application provides a method for preparing granular magnesium fertilizer, comprising the following steps:

[0010] mixing magnesium sulfate monohydrate, light-burned magnesium oxide, and a solvent to form a mixed material; and

[0011] The mixed material is extruded and granulated by adopting a double-roll extrusion process.

[0012] In some embodiments, the mass ratio of the magnesium sulfate monohydrate to the light-burned magnesium oxide is approximately (45-95): (5-55).

[0013] In some embodiments, the mass ratio of the total mass of the magnesium sulfate monohydrate and the light-burned magnesium oxide to the solvent is about 100:(1-10).

[0014] In some embodiments, the step of extruding and granulating the mixed material using a double-roll extrusion process includes:

[0015] The mixed material is squeezed through a pair of rollers to form granular agglomerates;

[0016] drying the granular agglomerates to form dry granules; and

[0017] The dried particles are sieved to prepare the granular magnesium fertilizer.

[0018] In some embodiments, the pressure of the roller pressing is about 6 MPa to 12 MPa.

[0019] In some embodiments, the solvent includes one or more of water, sodium chloride solution, potassium chloride solution, calcium chloride solution, and silver nitrate solution.

[0020] In some embodiments, the magnesium sulfate monohydrate is powdered magnesium sulfate monohydrate, and the particle size of the powdered magnesium sulfate monohydrate is about 0.1 mm to 1.5 mm.

[0021] In some embodiments, the mass percentage of water-soluble magnesium oxide in the powdered magnesium sulfate monohydrate is about 20% to 29%.

[0022] In some embodiments, the light-burned magnesium oxide is powdered light-burned magnesium oxide, and the particle size of the powdered light-burned magnesium oxide is about 0.1 mm to 0.2 mm.

[0023] In some embodiments, the mass percentage of citric acid-soluble magnesium oxide in the powdered light-burned magnesium oxide is about 70% to 90%.

[0024] In a second aspect, the present application provides a granular magnesium fertilizer comprising, by weight, approximately 45 to 95 parts of magnesium sulfate monohydrate and approximately 5 to 55 parts of light-burned magnesium oxide.

[0025] In some embodiments, the granular magnesium fertilizer has a moisture content of less than about 1.0%.

[0026] In some embodiments, the particle size of the granular magnesium fertilizer is about 1.0 mm to 4.75 mm.

[0027] In a third aspect, the present application provides a blended fertilizer comprising the granular magnesium fertilizer described in the second aspect.

[0028] In a fourth aspect, the present application provides a nitrogen-magnesium compound fertilizer, including the granular magnesium fertilizer described in the second aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the conventional technology, the following briefly introduces the drawings required for use in the embodiments or the conventional technology descriptions. Obviously, the drawings described below are merely embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the disclosed drawings without any creative work.

[0030] FIG1 is a process flow chart for preparing granular magnesium fertilizer in Example 1 of the present application;

[0031] Figure 2 is a physical picture of the blended fertilizer A formed based on Example 1 and the blended fertilizer B formed based on Comparative Example 1 in the present application; wherein, (a) in Figure 2 is a physical picture of the blended fertilizer A after being placed for 4 months; (b) in Figure 2 and (c) in Figure 2 are physical pictures of the blended fertilizer B after being placed for 3 days and 6 days, respectively. DETAILED DESCRIPTION

[0032] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0033] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application pertains. The terms used herein in the specification of this application are for the purpose of describing specific embodiments only and are not intended to limit this application.

[0034] The International Magnesium Institute (IMI) conducted research on soil magnesium supply capacity and the effects of magnesium application on various crops in different regions of China. The results of trials on approximately 200 crops across different regions found that adding magnesium to NPK fertilizers significantly improved crop yield and quality compared to applying NPK fertilizers alone. The average yield increase was approximately 9.8%, with magnesium application resulting in yield increases of over 10%. Furthermore, the application of magnesium fertilizers also improved agricultural product quality, such as improving melon shape, increasing vitamin C and protein content, and accelerating color change, thereby increasing farmers' profits.

[0035] The study also found that adding magnesium to nitrogen, phosphorus and potassium fertilizers significantly improved the absorption and utilization rate of nitrogen, phosphorus and potassium fertilizers. The mechanism is as follows:

[0036] Magnesium can promote the absorption of nitrate nitrogen by crops. Ammonium-loving crops such as tea and rice can increase their absorption of ammonium nitrogen when magnesium is applied. From the perspective of nitrogen fertilizer utilization, the largest destination for nitrogen assimilation by crops after absorbing it is protein synthesis. Approximately 80%-85% of inorganic nitrogen is converted into protein in plants. Magnesium is essential for the conversion of inorganic nitrogen, such as ammonium nitrogen and nitrate nitrogen, into protein in plants. Studies have shown that when plants are magnesium deficient, the pathway from inorganic nitrogen to protein is blocked. In other words, the nitrogen absorbed by the plant cannot be converted into protein, which greatly reduces the plant's nitrogen utilization efficiency. When nitrogen utilization cannot be carried out efficiently, it will feedback regulate the root system to reduce nitrogen absorption from the soil, thereby reducing the crop's nitrogen absorption efficiency from the soil.

[0037] The application of magnesium fertilizer can also improve the absorption and utilization efficiency of crops for phosphorus. Phosphorus is the least efficient element among the three major nutrients of nitrogen, phosphorus and potassium. This is mainly because phosphorus is easily fixed in the soil, and phosphorus that cannot be reached by the roots cannot be absorbed. The application of magnesium fertilizer can promote the growth of crop roots and increase the ability to obtain phosphorus in the soil. In addition, studies have found that magnesium can promote the secretion of more organic acids such as malic acid and citric acid in the plant rhizosphere, thereby enhancing the ability to activate phosphorus in the soil. In addition, studies have found that magnesium is also a carrier for phosphorus transport across the membrane in root cells, thereby increasing the absorption of phosphorus in the soil. In terms of phosphorus utilization, the assimilation of phosphorus in plants also requires the participation of magnesium, such as the formation of Mg-ATP, the most important energy substance in plants.

[0038] During crop growth, a key function of potassium is to serve as a carrier for the transport of photosynthate. In addition to the carrier, the transport of photosynthate also requires energy substances combined with magnesium to provide energy for transportation. Therefore, sufficient magnesium can ensure an adequate supply of energy substances to improve the efficiency of photosynthate transport, that is, the efficiency of potassium in this function.

[0039] Furthermore, since magnesium is currently a shortcoming in soil supply and fertilization management, addressing this shortcoming will promote overall crop growth and improve the absorption and utilization rate of soil and applied fertilizers. According to IMI research, to address this nutritional shortfall in magnesium, approximately 4 million tons of magnesium nutrients (calculated as MgO) need to be introduced annually through fertilization. However, the current input of magnesium fertilizer in agricultural production is less than 100,000 tons (calculated as MgO), far from meeting the demand for magnesium in agricultural production. Given the status of soil magnesium deficiency and the effectiveness of magnesium application, fertilization and magnesium addition are of great significance to agricultural production.

[0040] In order to achieve the goal of adding magnesium to agricultural fertilization more quickly to fill the nutritional gap and improve agricultural production efficiency, four problems need to be solved:

[0041] 1. Recognize the problem of magnesium deficiency in crops and understand that magnesium supplementation can increase crop yield and quality and improve the efficiency of nitrogen, phosphorus and potassium fertilizers.

[0042] Second, spread the value of adding magnesium to fertilizers, so that farmers realize that in addition to the nitrogen, phosphorus and potassium they are used to applying, increasing the application of magnesium fertilizers can solve problems such as crop yellowing, meet the demand for early market launch, and improve yield and quality, so that they realize the necessity and value of applying magnesium-containing fertilizers.

[0043] 3. Provide suitable magnesium-containing fertilizer products. At present, simplifying fertilization is an extremely important demand, and the consumption of compound fertilizers has increased year by year. Blended fertilizers are granular fertilizers made by dry mixing with nitrogen, phosphorus and potassium as the main nutrients (GB / T21633-2020 blended fertilizers (BB fertilizers)), which are a type of compound fertilizer. China's annual consumption of blended fertilizers is more than 10 million tons, which also meets the current needs of growers for simplified fertilization. Wheat, corn and peanuts in Northeast and North China, as well as rice in some areas of the south, all have the habit of applying blended fertilizers. Therefore, from the perspective of "suitable products", in addition to spreading granular magnesium fertilizers alone to supplement the lack of magnesium in the soil, adding sufficient magnesium elements to blended fertilizers according to crop needs not only meets the plant's demand for nutrients, but also meets the actual needs of growers for simplified fertilization in agricultural production.

[0044] Fourth, how to achieve the addition of magnesium to blended fertilizers. Through research in this application, it was found that there are two technical problems to be solved: one is the selection of magnesium raw materials. Based on the severity of magnesium deficiency, rapid and effective magnesium supplementation is the only way. Magnesium fertilizers need to be soluble in the soil aqueous solution to effectively supply magnesium nutrients. Sources of magnesium fertilizers with water-soluble characteristics include magnesium sulfate, magnesium chloride, and magnesium nitrate. Magnesium sulfate is a type of water-soluble magnesium fertilizer and can provide crops with the necessary magnesium and sulfur elements; magnesium chloride has strong hygroscopicity, is prone to deliquesce and agglomerate, and is not an ideal fertilizer composition; magnesium nitrate has good water solubility, but similar to magnesium chloride, it has strong hygroscopicity and is prone to agglomeration. Therefore, magnesium sulfate has higher nutrient effectiveness and stability as an agricultural fertilizer. The second is the stability of the blended fertilizer particles after adding magnesium. Blended fertilizers often need to be bagged and the transportation distance and storage time are relatively long. The influence of their chemical compatibility is more important, which is mainly manifested in two aspects: hygroscopic deliquesce or agglomeration after blending, and nutrient loss (ammonia volatilization and degradation of water-soluble phosphorus). Hygroscopicity in blended fertilizers generally manifests in two ways: first, the critical relative humidity (above which fertilizers naturally absorb water) of the blended fertilizer decreases, or compounds are formed that are more hygroscopic; second, the release of crystal water as free water (GB / T 21633-2020 Blended Fertilizers (BB Fertilizers)). Therefore, magnesium to be incorporated into blended fertilizers must possess the following properties: 1) a high critical relative humidity; 2) a low internal moisture content; and 3) difficulty in releasing crystal water.

[0045] Traditional methods for preparing magnesium sulfate granules are usually wet or dry methods, but the wet method can cause the moisture content in the magnesium sulfate granules to be too high, while the dry method cannot produce shaped magnesium sulfate granules or the produced magnesium sulfate granules have poor formability. To this end, the present application provides a method for preparing granular magnesium fertilizer. The granular magnesium fertilizer produced using the preparation method provided in this application possesses the unique properties required for the above-mentioned blended fertilizer raw materials, becoming a stable blended fertilizer magnesium raw material.

[0046] In a first aspect, the present application provides a method for preparing granular magnesium fertilizer, comprising the following steps:

[0047] mixing magnesium sulfate monohydrate, light-burned magnesium oxide, and a solvent to form a mixed material; and

[0048] The mixed material is extruded and granulated using a double-roll extrusion process.

[0049] The preparation method of granular magnesium fertilizer provided in the present application adopts a double-roller extrusion process between the dry and wet processes to granulate the granular magnesium fertilizer, which effectively solves the problems of excessive moisture content in the granular magnesium fertilizer in the wet granulation process and the inability to form or poor forming stability in the dry granulation process, thereby producing a granular magnesium fertilizer with excellent fertilizer efficiency and forming stability, which can be fully used in blended fertilizers to promote the absorption of elements such as nitrogen, phosphorus and potassium by crops while supplementing magnesium.

[0050] In addition, the present application uses magnesium sulfate monohydrate and light-burned magnesium oxide as raw materials to undergo a partial hydration reaction under the action of a solvent to form an air-hardening gelling material with a structure of MgO-MgSO4-H2O ternary system. This air-hardening gelling material can make the granular magnesium fertilizer composed of magnesium sulfate monohydrate and light-burned magnesium oxide still have high strength after the water evaporates, so that it can be stably formed, meeting the needs of mixing, storage, transportation and application of granular magnesium fertilizer. The magnesium particles produced by the present application contain both magnesium sulfate monohydrate and a small amount of light-burned magnesium oxide, so that the granular magnesium fertilizer has both the fast-acting effect of magnesium sulfate monohydrate and the long-lasting slow-release effect of light-burned magnesium oxide. This feature enables the magnesium element in the particles to be released and act on each growth cycle of the crop, and to be mixed in sufficient amount according to the crop's demand for magnesium, meeting the 4R principles of scientific fertilization: the right source, the right time of fertilization, and the right rate. Furthermore, light-burned magnesium oxide is a citrate-soluble magnesium fertilizer that slowly releases magnesium nutrients in acidic soils, exhibiting a certain slow-release property. Therefore, it can effectively reduce magnesium leaching or runoff losses in agricultural production conditions with high rainfall. Furthermore, the granular magnesium fertilizer provided in this application also contains sulfur, which not only supplements magnesium but also provides essential sulfur for crops.

[0051] It should be noted that in the present application, magnesium sulfate monohydrate can be made of natural magnesia ore crystal powder (Kieserit), which is a natural mineral raw material, or magnesium sulfate monohydrate prepared by chemical synthesis of natural magnesia ore crystal powder; and light-burned magnesium oxide is a natural mineral raw material obtained by calcining natural dolomite ore.

[0052] In the granular magnesium fertilizer provided in the present application, the ratio of magnesium sulfate monohydrate and light-burned magnesium oxide can be flexibly adjusted to produce granular magnesium fertilizer suitable for various soil conditions.

[0053] In some embodiments, the mass ratio of magnesium sulfate monohydrate to light-burned magnesium oxide is about (45-95): (5-55).

[0054] In some embodiments, the mass ratio of the total mass of magnesium sulfate monohydrate and light-burned magnesium oxide to the solvent is about 100:(1-10).

[0055] In the present application, the solvent is mainly an inorganic solvent. The role of the solvent is mainly to play a hydration effect to assist granulation. Among them, the inorganic solvent includes one or more of water, sodium chloride solution (salt water), potassium chloride solution, calcium chloride solution and silver nitrate solution. In some embodiments, the solvent is water.

[0056] In some embodiments, the step of extruding and granulating the mixed material using a double-roll extrusion process includes:

[0057] The mixed material is squeezed through a pair of rollers to form granular agglomerates;

[0058] drying the granular agglomerates to form dry granules; and

[0059] The dried granules are screened to prepare granular magnesium fertilizer.

[0060] In some embodiments, the conditions of the roll extrusion process include:

[0061] The temperature is room temperature and the pressure is about 6MPa to 12MPa.

[0062] It is understood that "normal temperature" generally refers to about 4°C to about 35°C, for example, about 20°C ± about 5°C. In some embodiments, "normal temperature" refers to about 10°C to about 30°C. In some embodiments, "normal temperature" refers to about 20°C to about 30°C.

[0063] In some embodiments, the drying method is heat drying, wherein the heat drying temperature can be about 80° C. to 140° C., and the drying time can be about 0.25 h to 0.5 h.

[0064] In some embodiments, the magnesium sulfate monohydrate is powdered magnesium sulfate monohydrate, and the particle size of the powdered magnesium sulfate monohydrate is about 0.1 mm to 1.5 mm.

[0065] In some embodiments, the mass percentage of water-soluble magnesium oxide in the powdered magnesium sulfate monohydrate is about 20% to 29%.

[0066] In the present application, the water-soluble magnesium oxide in magnesium sulfate monohydrate is measured by the method provided by standards EN 15961-2017 and EN11885:2009-09 or standard GB / T 26568-2011.

[0067] In some embodiments, the light-burned magnesium oxide is powdered light-burned magnesium oxide, and the particle size of the powdered light-burned magnesium oxide is about 0.1 mm to 0.2 mm. Compared with granular light-burned magnesium oxide, powdered light-burned magnesium oxide has a better magnesium element release effect. Traditional powdered light-burned magnesium oxide is not suitable for agricultural mechanized production. Through the preparation method adopted in this application, powdered light-burned magnesium oxide is mixed with water-soluble powdered magnesium sulfate monohydrate to form granular magnesium fertilizer. After being applied to the soil, as magnesium sulfate monohydrate gradually decomposes in the soil, the surface tension of the granular magnesium fertilizer is eliminated, so that the light-burned magnesium oxide powder can be dispersed in the soil, which is conducive to being absorbed by the soil and crops.

[0068] In some embodiments, the mass percentage of citric acid-soluble magnesium oxide in the powdered light-burned magnesium oxide is about 70% to 90%.

[0069] It is understood that after screening, the granular magnesium fertilizer that does not meet the particle size can be crushed and then rolled again. In addition, after screening, the steps of polishing, secondary screening and packaging can also be included.

[0070] In some embodiments, the method for preparing granular magnesium fertilizer comprises the following steps:

[0071] 1) mixing magnesium sulfate monohydrate and light-burned magnesium oxide to form a dry material;

[0072] 2) mixing the dry material with a granulation aid to form a mixed material;

[0073] 3) The mixed material is squeezed through a pair of rollers to form granular agglomerates;

[0074] 4) drying the granular agglomerates to form dry granules; and

[0075] 5) Screening the dried granules to prepare granular magnesium fertilizer.

[0076] In a second aspect, the present application provides a granular magnesium fertilizer comprising, by weight, approximately 45 to 95 parts of magnesium sulfate monohydrate and approximately 5 to 55 parts of light-burned magnesium oxide.

[0077] In the granular magnesium fertilizer provided in the present application, the ratio of magnesium sulfate monohydrate and light-burned magnesium oxide can be flexibly adjusted to produce granular magnesium fertilizer suitable for various soil conditions.

[0078] In some embodiments, the granular magnesium fertilizer has a moisture content of less than about 1.0%.

[0079] In some embodiments, the granular magnesium fertilizer has a moisture content of less than about 0.5%.

[0080] In some embodiments, the particle size of the granular magnesium fertilizer is about 1.0 mm to 4.75 mm.

[0081] In a third aspect, the present application provides a blended fertilizer comprising the granular magnesium fertilizer according to the second aspect.

[0082] In the present application, the blended fertilizer may include at least two of the following: phosphate fertilizer, potash fertilizer, and nitrogen fertilizer. The blended fertilizer provided herein, because it is blended with the granular magnesium fertilizer provided herein, can avoid the problem of moisture and clumping that can occur when magnesium fertilizer granules prepared by other preparation methods are added to the blended fertilizer, and has excellent stability.

[0083] In some embodiments, the blended fertilizer includes the following components in the following mass percentages:

[0084] Phosphate fertilizer is about 0-90%, potash fertilizer is about 0-90%, nitrogen fertilizer is about 0-90% and granular magnesium fertilizer is about 7%-50%, and the mass percentages of the phosphate fertilizer, potash fertilizer and nitrogen fertilizer are not all 0.

[0085] In this application, the specific composition of the phosphate fertilizer, potash fertilizer, and nitrogen fertilizer is not limited, and fertilizers commonly used in the field of agricultural fertilizers can be selected. For example, the phosphate fertilizer can be diammonium phosphate; the potash fertilizer can be potassium chloride or potassium sulfate; and the nitrogen fertilizer can be urea or ammonium sulfate.

[0086] In a fourth aspect, the present application provides a nitrogen-magnesium compound fertilizer, including the granular magnesium fertilizer of the second aspect.

[0087] Nitrogen fertilizer itself has the characteristic of easily absorbing moisture and agglomerating, and is prone to moisture absorption and agglomeration when mixed with magnesium fertilizer particles prepared by other commonly used methods. However, the granular magnesium fertilizer provided in this application can be stably blended with nitrogen fertilizer, thereby avoiding the problem of nitrogen fertilizer easily absorbing moisture and agglomerating, and improving its stability.

[0088] The present application will be further described in detail below with reference to specific examples. It should be understood that these examples are intended to illustrate the present application only and are not intended to limit the scope of the present application. For experimental methods in the following examples where specific conditions are not specified, reference should be made to the instructions provided in this application, or to experimental manuals or conventional conditions in the art, or to conditions recommended by the manufacturer, or to experimental methods known in the art.

[0089] In the following specific examples, the measured parameters of raw material components may have slight deviations within the range of weighing accuracy unless otherwise specified. For temperature and time parameters, acceptable deviations caused by instrument testing accuracy or operational accuracy are allowed.

[0090] Example 1

[0091] Preparation of natural magnesium sulfate ore crystal powder. The steps are as follows: The process flow of electrostatic separation technology can be found in the document "Ullmann Encyclopedia of Industrial Chemistry Wiley-VCH Verlag GmbH & Co. KGaA: Weinheim, Germany, 2016; pp. 1–35. ISBN 978-3-527-30673-2, the author of the document "Electrostatic Separation" is M.; Wachsmuth, U.; Waldmann, L.; Flachberger, H.; Mirkowska, M.; Brands, L.; Beier, P.-M.; Stahl, I. ". For further information, see page 22 for the separation of kieserite using electrostatic separation (ESTA) technology.

[0092] The process flow chart for preparing granular magnesium sulfate fertilizer in this application is shown in Figure 1. The steps are as follows:

[0093] Approximately 90 parts of natural magnesium sulfate ore crystal powder (raw material 1) and approximately 10 parts of light-burned magnesium oxide powder (raw material 2) are thoroughly mixed in a spiral mixer, and approximately 5 parts of water are added and stirred uniformly to form a mixture. The mixture is then introduced into a roller die-pressing granulator. The torque and thrust of the roller die-pressing extrusion device and the hydration reaction of the solvent water cause the mixture to agglomerate together to form high-density granular agglomerates. The resulting high-density granular agglomerates are then placed in a rotary drying kiln and hot-air dried at approximately 120°C to remove moisture from the agglomerates, reducing the moisture content to approximately 0.5%. The dehydrated agglomerates are then cooled, sieved, and polished to produce granular magnesium fertilizer with a particle size of approximately 1.0 mm to 4.75 mm.

[0094] Optionally, the prepared granular magnesium fertilizer can also be dusted, packaged and stored.

[0095] Example 2

[0096] The preparation method of Example 2 is basically the same as that of Example 1, except that the contents of the components are different. The steps are as follows:

[0097] Approximately 65 parts of natural magnesium sulfate ore crystal powder (raw material 1) and approximately 35 parts of light-burned magnesium oxide powder (raw material 2) are thoroughly mixed in a spiral mixer, and approximately 5 parts of water are added and stirred uniformly to form a mixture. The mixture is then introduced into a roller die-pressing granulator. The torque and thrust of the roller die-pressing extrusion device and the hydration reaction of the solvent water cause the mixture to agglomerate together to form high-density granular agglomerates. The resulting high-density granular agglomerates are then placed in a rotary drying kiln and hot-air dried at approximately 120°C to remove moisture from the agglomerates, reducing the moisture content to approximately 0.5%. The dehydrated agglomerates are then cooled, sieved, and polished to produce granular magnesium fertilizer with a particle size of approximately 1.0 mm to 4.75 mm.

[0098] Optionally, the prepared granular magnesium fertilizer can also be dusted, packaged and stored.

[0099] Comparative Example 1

[0100] The granular magnesium fertilizer in Comparative Example 1 was prepared by a disc granulation process.

[0101] The test indicators of the granular magnesium fertilizer prepared in Example 1 are shown in Table 1.

[0102] Table 1

[0103] The test indicators of the granular magnesium fertilizer prepared in Example 2 are shown in Table 2.

[0104] Table 2

[0105] The granular magnesium fertilizers prepared in Example 1 and Comparative Example 1 were respectively blended with fertilizers containing nitrogen, phosphorus, and potassium to form blended fertilizers A and B. The two blended fertilizers were placed in a warehouse under the same conditions for observation. The observation results are shown in Figure 2, where (a) in Figure 2 is a physical picture of blended fertilizer A after 4 months of storage; (b) in Figure 2 and (c) in Figure 2 are physical pictures of blended fertilizer B after 3 days and 6 days of storage, respectively. As can be seen from Figure 2, the granular magnesium fertilizer prepared in this application does not absorb moisture and agglomerate when used in blended fertilizers; while the granular magnesium fertilizer prepared in Comparative Example 1 will cause serious agglomeration of the blended fertilizer after being used in blended fertilizers.

[0106] Field trial effect test:

[0107] 1) Planting area: Hanting District, Weifang City; Planting crop: Provence tomatoes. The experiment was conducted with three treatment areas, each with an area of ​​approximately 30 m 2, each area was treated 3 times, and the blocks were arranged randomly. Before planting crops, farmyard manure (about 3000kg / mu) was uniformly applied in the three treatment areas as base fertilizer. Then, compound fertilizer 15-15-15 was applied in the first treatment area (treatment 1), and the application amount was about 80kg / mu, and the granular magnesium fertilizer prepared in Example 1 was applied at the same time, and the fertilization standard was about 50kg / mu; in the second treatment area (treatment 2, conventional fertilization group), compound fertilizer 15-15-15 was applied at the bottom, and the fertilization standard was about 80kg / mu; the third treatment area (treatment 3) was not fertilized (control group). Two days later, tomatoes were transplanted and planted, and water was poured for planting. After 2 months, the yield was measured for the first time; after 4 months, the yield was measured.

[0108] 2) Planting area: Xiashan District, Weifang City; Planting crop: Provence tomatoes. The experiment was conducted in three treatment areas, each with an area of ​​approximately 30 m 2 , each area was treated 3 times, and the blocks were arranged randomly. Before planting crops, farmyard manure (about 3000kg / mu) was uniformly applied in the three treatment areas as base fertilizer. Then, compound fertilizer 15-15-15 was applied in the first treatment area (treatment 1), and the fertilization standard was about 80kg / mu, and the granular magnesium fertilizer prepared in Example 1 was applied at the same time, and the fertilization standard was about 50kg / mu; in the second treatment area (treatment 2, conventional fertilization group), compound fertilizer 15-15-15 was applied at the bottom, and the fertilization standard was about 80kg / mu; the third treatment area (treatment 3) was not fertilized (control group). Two days later, tomatoes were transplanted and planted, and watered. After 2 months, the yield was measured for the first time; after 4 months, the yield was measured.

[0109] 3) Planting area: Jinjiang Town, Chengmai County; Planting crop: Ge 68 You 9938 rice. At the time of transplanting, the rice had approximately 3.5 leaves and the seedling height was approximately 16.5 cm. The experiment had three treatment areas, each with an area of ​​approximately 20 m 2, each area was treated three times, and the blocks were randomly arranged. Then, conventional fertilizers (urea, superphosphate, and potassium chloride) were applied in the first treatment area (treatment 1), and the granular magnesium fertilizer prepared in Example 1 was applied as a bottom fertilizer. The fertilization standard of the bottom-applied granular magnesium fertilizer was about 25 kg / mu. The fertilization steps in the first treatment area were as follows: superphosphate and granular magnesium fertilizer were applied as base fertilizer once, and urea and potassium chloride were applied at about 30% and about 10% of the base fertilizer content, respectively; urea and potassium chloride were applied at about 60% and about 30% of the base fertilizer content, respectively, 7 days after the rice was transplanted; urea and potassium chloride were applied at about 10% and about 60% of the base fertilizer content, respectively, 25 days after the rice was transplanted; conventional fertilizers (urea, superphosphate, and potassium chloride) were applied in the second treatment area (treatment 2, conventional fertilization group). The second treatment area was fertilized as follows: superphosphate was applied as a base fertilizer once, followed by urea and potassium chloride at approximately 30% and 10% of the base fertilizer content, respectively. Seven days after transplanting, urea and potassium chloride were applied at approximately 60% and 30% of the base fertilizer, respectively. Twenty-five days after transplanting, urea and potassium chloride were applied again at approximately 10% and 60% of the base fertilizer, respectively. The third treatment area (Treatment 3) received no fertilizer (control group). Three months later, each treatment area was harvested and yield measured.

[0110] 4) Planting area: Dongshan Town, Haikou City; Planting crop: Boyu 707 rice. At the time of transplanting, the rice had approximately 3.5 leaves and the seedling height was approximately 16.5 cm. The experiment had three treatment areas, each with an area of ​​approximately 20 m 2 , each area was treated three times, and the blocks were randomly arranged. Then, conventional fertilizers (urea, superphosphate, and potassium chloride) were applied in the first treatment area (treatment 1), and the granular magnesium fertilizer prepared in Example 1 was applied as a bottom fertilizer. The fertilization standard of the bottom-applied granular magnesium fertilizer was about 25 kg / mu. The fertilization steps in the first treatment area were as follows: superphosphate and granular magnesium fertilizer were applied as base fertilizer once, and urea and potassium chloride were applied at about 30% and about 10% of the base fertilizer content, respectively; urea and potassium chloride were applied at about 60% and about 30% of the base fertilizer content, respectively, 7 days after the rice was transplanted; urea and potassium chloride were applied at about 10% and about 60% of the base fertilizer content, respectively, 25 days after the rice was transplanted; conventional fertilizers (urea, superphosphate, and potassium chloride) were applied in the second treatment area (treatment 2, conventional fertilization group). The second treatment area was fertilized as follows: superphosphate was applied as a base fertilizer once, followed by urea and potassium chloride at approximately 30% and 10% of the base fertilizer content, respectively. Seven days after transplanting, urea and potassium chloride were applied at approximately 60% and 30% of the base fertilizer, respectively. Twenty-five days after transplanting, urea and potassium chloride were applied again at approximately 10% and 60% of the base fertilizer, respectively. The third treatment area (Treatment 3) received no fertilizer (control group). Three months later, each treatment area was harvested and yield measured.

[0111] 5) Planting area: Daqiao Township, Weishi County, Henan Province; Planting crop: Degao Xialong No. 18 rapeseed. The experiment was conducted in three treatment areas, each with an area of ​​approximately 30m 2 , each area was treated three times, and the blocks were arranged randomly. Before planting crops, farmyard manure (about 150 kg / mu) was uniformly applied as base fertilizer in the three treatment areas. No topdressing was done during the growth period. Then, compound fertilizer 17-17-17 was applied in the first treatment area (treatment 1), and the granular magnesium fertilizer prepared in Example 1 was applied at the same time, with a fertilization standard of about 10 kg / mu; in the second treatment area (treatment 2, conventional fertilization group), compound fertilizer 17-17-17 was applied at the bottom, and an equal amount of fine sand was applied at the bottom of the first treatment area during the same period; compound fertilizer 17-17-17 was applied in the third treatment area (treatment 3). Sow seeds two days later; harvest once after 25 days; and record the actual yield by zone at harvest. Except for spraying fertilizer solution or water according to the plan, other management measures were the same as those for conventional rapeseed field production.

[0112] 6) Planting area: Dameng Town, Zhongmu County, Henan Province; Planting crop: Summer Taste No. 2 rapeseed. The experiment was conducted in three treatment areas, each with an area of ​​approximately 30 m 2 , each area was treated 3 times, and the blocks were arranged randomly. Before planting crops, farmyard manure (about 150kg / mu) was uniformly applied in the three treatment areas as base fertilizer. Then in the first treatment area (treatment 1), about 25kg of compound fertilizer 16-16-16 was applied at the bottom, and about 20kg of nitro-compound fertilizer 25-9-9 was applied per mu, and the granular magnesium fertilizer prepared in Example 1 was applied at the bottom at the same time, and the fertilization standard was about 10kg / mu; in the second treatment area (treatment 2, conventional fertilization group), about 25kg of compound fertilizer 16-16-16 was applied at the bottom, and about 20kg of nitro-compound fertilizer 25-9-9 was applied per mu, and an equal amount of fine sand was applied at the bottom in the same period as in the first treatment area; in the third treatment area (treatment 3), about 25kg of compound fertilizer 16-16-16 was applied at the bottom, and about 20kg of nitro-compound fertilizer 25-9-9 was applied per mu. Sow after two days; harvest at one time after 30 days; and record the actual yield by zone at harvest. In addition to spraying fertilizer solution or water according to the plan, other management measures were the same as those in conventional rapeseed field production.

[0113] The crop yield increase rates obtained under different fertilization conditions in different experimental areas are shown in Table 3.

[0114] Table 3

[0115] As can be seen from the table above, the granular magnesium fertilizer provided by this application is suitable for a variety of crops as a magnesium fertilizer. Compared with local conventional fertilization, the average yield increase rate is greater than 9.3%, with a significant income-increasing effect. As can be seen from the above blending tests and fertilizer efficiency tests, the granular magnesium fertilizer provided by this application is a blendable and highly nutrient-efficient magnesium fertilizer product.

[0116] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0117] The above-described embodiments merely represent several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that a person of ordinary skill in the art may make various modifications and improvements without departing from the spirit of the present application, and these modifications and improvements fall within the scope of protection of the present application. Therefore, the scope of protection of the present patent application shall be determined by the appended claims.

Claims

1. A method for preparing granular magnesium fertilizer, characterized in that: The following steps are involved: Mixing magnesium sulfate monohydrate, light-burned magnesium oxide and a solvent to form a mixed material; and The mixed material is extruded and granulated by a double-roll extrusion process.

2. The preparation method according to claim 1, characterized in that The mass ratio of the magnesium sulfate monohydrate to the light-burned magnesium oxide is approximately (45-95):(5-55).

3. The preparation method according to claim 1 or 2, characterized in that: The mass ratio of the total mass of the magnesium sulfate monohydrate and the light-burned magnesium oxide to the solvent is about 100:(1-10).

4. The preparation method according to any one of claims 1 to 3, characterized in that: The step of extruding and granulating the mixed material by a double-roll extrusion process comprises: The mixed material is squeezed through a pair of rollers to form granular agglomerates; drying the granular agglomerates to form dry granules; and The dried particles are screened to prepare the granular magnesium fertilizer.

5. The preparation method according to any one of claims 1 to 4, characterized in that: The pressure of the roller extrusion is about 6MPa to 12MPa.

6. The preparation method according to any one of claims 1 to 5, characterized in that: The solvent includes one or more of water, sodium chloride solution, potassium chloride solution, calcium chloride solution and silver nitrate solution.

7. The preparation method according to any one of claims 1 to 6, characterized in that: The magnesium sulfate monohydrate is powdered magnesium sulfate monohydrate, and the particle size of the powdered magnesium sulfate monohydrate is about 0.1 mm to 1.5 mm.

8. The preparation method according to claim 7, characterized in that: In the powdered magnesium sulfate monohydrate, the mass percentage of water-soluble magnesium oxide is about 20% to 29%.

9. The preparation method according to any one of claims 1 to 8, characterized in that: The light-burned magnesium oxide is powdered light-burned magnesium oxide, and the particle size of the powdered light-burned magnesium oxide is about 0.1 mm to 0.2 mm.

10. The preparation method according to claim 9, characterized in that: In the powdery light-burned magnesium oxide, the mass percentage of citric acid-soluble magnesium oxide is about 70% to 90%.

11. A granular magnesium fertilizer, characterized in that: Calculated by weight, the composition comprises about 45 to 95 parts of magnesium sulfate monohydrate and about 5 to 55 parts of light-burned magnesium oxide.

12. The granular magnesium fertilizer according to claim 11, characterized in that The moisture content of the granular magnesium fertilizer is about <1.0%.

13. The granular magnesium fertilizer according to claim 11 or 12, characterized in that: The particle size of the granular magnesium fertilizer is about 1.0 mm to 4.75 mm.

14. A blended fertilizer, characterized in that: The invention relates to a granular magnesium fertilizer comprising the granular magnesium fertilizer according to any one of claims 11 to 13.

15. A nitrogen-magnesium compound fertilizer, characterized in that: The invention relates to a granular magnesium fertilizer comprising the granular magnesium fertilizer according to any one of claims 11 to 13.

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