A synergistic potassium-magnesium sulfate type compound fertilizer and a preparation method thereof

Abstract

The application discloses a synergistically enhanced potassium-magnesium sulfate type compound fertilizer and a preparation method thereof, and belongs to the technical field of potassium-magnesium sulfate type compound fertilizers. The synergistically enhanced potassium-magnesium sulfate type compound fertilizer is composed of the following components in parts by weight: 200-250 parts of potassium-magnesium sulfate, 600-700 parts of powdered potassium sulfate, 40-60 parts of ammonium polyphosphate modified magnesium oxide, 10-20 parts of potassium fulvate, and 80-120 parts of a magnesium chloride-citric acid compound solution. The ammonium polyphosphate modified magnesium oxide is introduced, the unique polyphosphate long-chain structure of the ammonium polyphosphate is used as an ion lock, magnesium ions are captured and chelated in situ at a fertilizer dissolving micro-interface, and a complex with strong anti-interference capability is formed; the magnesium in this form can effectively avoid the competitive inhibition of high-concentration potassium ions on root absorption channels.

Description

A synergistic potassium magnesium sulfate compound fertilizer and its preparation method Technical Field

[0001] This invention belongs to the technical field of potassium magnesium sulfate compound fertilizers, specifically, it relates to a synergistic potassium magnesium sulfate compound fertilizer and its preparation method. Background Technology

[0002] Potassium (K) is one of the three essential nutrients for plant growth and development, playing a crucial role in crop yield formation, quality improvement, transport of photosynthetic products, and enhancement of stress resistance. Magnesium (Mg), as the central atom of chlorophyll molecules, is a key driver of plant photosynthesis and energy metabolism. In agricultural production practices, with the continuous increase in crop yields and the large-scale input of nitrogen, phosphorus, and potassium fertilizers, crops are increasingly removing magnesium from the soil, leading to a continuous decline in the available magnesium content in the soil. This is particularly prevalent in acidic red soil areas and sandy soils in southern China, where strong leaching results in widespread magnesium deficiency, severely limiting further increases in crop yield and quality improvement.

[0003] To achieve a synergistic supply of potassium and magnesium nutrients, agricultural production often employs physical mixing, combining granular potassium sulfate with magnesium-containing fertilizers such as potassium magnesium sulfate. However, this simple physical mixing method faces serious structural and chemical stability defects in practical applications: due to significant differences in the density, particle size, and surface shape of the raw materials, the mixed fertilizer is prone to segregation and stratification during transportation, storage, and application, leading to uneven nutrient distribution in the field. More seriously, magnesium-containing raw materials, especially potassium magnesium sulfate, typically have a low critical relative humidity, making them highly susceptible to moisture absorption and clumping. This not only damages the physical properties of the fertilizer but can also clog fertilizer application machinery in severe cases, hindering mechanized operations.

[0004] To overcome the defects in physical properties, existing technologies, such as Chinese patent application CN108033862A, disclose a novel method for preparing high-strength spherical potassium sulfate particles. Specifically, it discloses the use of calcium oxide, magnesium oxide, and calcium sulfate hemihydrate as binders, and the adjustment of acidity with dilute sulfuric acid, to prepare spherical potassium sulfate particles by agglomeration. This technical solution utilizes the curing characteristics of inorganic cementing materials to improve the physical strength of the particles to a certain extent.

[0005] However, simply pursuing increased physical strength cannot solve the agronomic efficiency deficiencies of potassium and magnesium. According to plant nutrition theory, potassium and magnesium ions have a strong antagonistic effect during the absorption process by plant roots. When the potassium concentration in the soil solution is too high, it will significantly inhibit the absorption of magnesium by the roots, resulting in a situation where plants are still deficient in magnesium even after magnesium fertilizer is applied. Furthermore, although magnesium oxide is introduced as a binder, its main purpose is to utilize the hydration and hardening properties of MgO for granulation. When the magnesium element is released, it still exists in the form of free ions, which cannot avoid the competitive inhibition of magnesium absorption channels by high concentrations of potassium ions. Therefore, the problem of potassium-magnesium antagonism cannot be solved from a physiological mechanism perspective.

[0006] To address the issues of adhesion and synergistic effects during granulation, Chinese patent application CN118255630A discloses a method for manufacturing spherical potassium sulfate granules containing urea-formaldehyde nitrogen. The technical solution involves reacting urea and formaldehyde under acidic conditions to generate a urea-formaldehyde solution, which is then sprayed into a granulator to mix with powdered potassium sulfate for granulation. This solution utilizes the adhesive and film-forming properties of urea-formaldehyde resin, not only solving the problem of difficult potassium sulfate granulation but also endowing the fertilizer with a certain slow-release nitrogen function. However, urea-formaldehyde resin technology mainly focuses on the slow release of nitrogen and the physical shaping of granules. It offers no inspiration for resolving the specific contradiction in the potassium-magnesium compound fertilizer system, namely the high hygroscopicity of magnesium salts and the antagonism between potassium and magnesium. Although urea-formaldehyde resin has a certain degree of hydrophobicity, it is difficult to completely block the chain reaction of moisture absorption and agglomeration caused by the instability of the internal crystal water of potassium-magnesium sulfate. Furthermore, the above technical solution does not involve modifying the chemical form of magnesium, thus failing to change the absorption kinetics of magnesium in the rhizosphere. Therefore, it still falls short in improving the synergistic utilization rate of potassium and magnesium.

[0007] In addition, there are some technical solutions, such as Chinese patent application CN120817830A, which discloses a boron-zinc-molybdenum synergistic compound fertilizer and its preparation process. It uses micronization technology to prepare micro-elements into a suspension with D90≤10μm, and uses biostimulants and special coating structures to achieve synergistic effects of multiple elements. However, the above technology is mainly for micro-elements such as B, Zn, and Mo used in very small amounts. If the micronized suspension technology is directly applied to the composite granulation of magnesium, which is a medium element, and potassium, a macro element, the amount of magnesium added is much higher than that of micro-elements. If a full suspension spraying process is used, too much liquid phase will be introduced, resulting in an imbalance of the liquid-solid ratio in the granulation system and difficulty in forming pellets. Even if a coating slow release can be achieved, it is still impossible to ensure that the absorption efficiency of magnesium is effectively protected in the rhizosphere environment where macro elements are released at high concentrations.

[0008] Therefore, developing a synergistic potassium magnesium sulfate compound fertilizer and its preparation method is of great significance for achieving synergistic and efficient utilization of potassium and magnesium nutrients and promoting the improvement of agricultural quality and efficiency. Summary of the Invention

[0009] To address the deficiencies in the aforementioned technical solutions, the present invention aims to provide a synergistic potassium magnesium sulfate compound fertilizer and its preparation method.

[0010] To achieve the above objectives, the present invention provides a synergistic potassium magnesium sulfate compound fertilizer, which, by weight, comprises the following raw materials: 200-250 parts potassium magnesium sulfate, 600-700 parts powdered potassium sulfate, 40-60 parts ammonium polyphosphate modified magnesium oxide, 10-20 parts potassium humate, and 80-120 parts magnesium chloride-citric acid composite solution.

[0011] The magnesium chloride-citric acid composite solution is a mixture prepared by dissolving 2%-5% anhydrous citric acid in a magnesium chloride aqueous solution with a mass concentration of 20%-25%.

[0012] The pH value of the magnesium chloride-citric acid composite solution is controlled between 4.0 and 5.0;

[0013] The powdered potassium sulfate is agricultural grade potassium sulfate produced by the Mannheim process and treated by air jet milling, with a potassium oxide content ≥50% and a particle size distribution D90 ≤0.15mm;

[0014] The moisture content of the powdered potassium sulfate is ≤0.5%;

[0015] The potassium magnesium sulfate is a double salt of magnesium sulfate monohydrate and potassium sulfate from natural pyromagnesia ore, with a magnesium oxide content ≥8% and a sulfur content ≥14%.

[0016] The potassium humate is: biochemical potassium humate, with a water-insoluble content ≤1.0% and a component proportion ≥70% of the components with a molecular weight distribution between 300-1000 Daltons.

[0017] The ammonium polyphosphate-modified magnesium oxide was prepared by the following method:

[0018] Step A: Take magnesium oxide and process it using an ultrafine pulverizer to make its particle size distribution D90≤20μm; place the powder in a high-speed mixer, add sodium dodecyl sulfate, and mix at high speed of 1500-2000 rpm for 3-5 minutes to reduce the surface energy of the powder and prevent agglomeration using surfactants.

[0019] Step B: Add ammonium polyphosphate solution to a jacketed reactor; heat to 45-50℃, start stirring, add trace amounts of additives to adjust viscosity, and prepare a modified activation solution with high wettability;

[0020] Step C: Place the magnesium oxide powder treated in Step A into the fluidization chamber of the fluidized bed coating machine; turn on the induced draft fan to fluidize the powder, and control the inlet air temperature at 60±2℃; uniformly spray the modified activating liquid from Step B onto the surface of the magnesium oxide particles at a rate of 15-20 ml / min using a pressure atomizing spray gun; the spraying amount is 10-15% of the magnesium oxide mass.

[0021] Step D: After spraying, maintain the fluidized state and continue the reaction for 15-20 minutes to form a stable chelated film; then heat to 80-85℃ for hot air drying until the moisture content is <1.0%, and pass through a 100-mesh sieve to obtain ammonium polyphosphate surface-activated modified magnesium oxide.

[0022] Furthermore, the magnesium oxide pulverized in step A is lightly calcined magnesium oxide with an activity of 60-65;

[0023] Furthermore, the mass of sodium dodecyl sulfate added in step A is 0.5% of the total mass of magnesium oxide;

[0024] Furthermore, the degree of polymerization of the ammonium polyphosphate solution added in step B is ≥3, and the P2O5 content is ≥30%.

[0025] Furthermore, the trace additive in step B is ethylene glycol, and the viscosity is adjusted to 150-200 cps.

[0026] A method for preparing a synergistic potassium magnesium sulfate compound fertilizer includes the following steps:

[0027] Step 1: Weigh out the powdered potassium sulfate, potassium magnesium sulfate, ammonium polyphosphate modified magnesium oxide, and potassium humate into a twin-shaft paddle mixer; mix for 8-10 minutes at a speed of 45-50 rpm to ensure that the modified magnesium oxide powder is evenly filled in the gaps between the potassium fertilizer and magnesium fertilizer particles, forming a dense microstructure.

[0028] Step 2: Continuously feed the mixture from Step 1 into a rotary drum granulator; start the granulator and control the rotation speed at 10-15 rpm; continuously spray a magnesium chloride-citric acid composite solution onto the material bed through a high-pressure atomizing nozzle, with the spray volume being 8-12% of the total powder mass;

[0029] Step 3: Control the material temperature inside the granulator at 50-65℃, and the material residence time inside the machine is 10-15 minutes; during this process, MgCl2 in the magnesium chloride-citric acid composite solution reacts rapidly with the active MgO in the ammonium polyphosphate modified magnesium oxide, strongly agglomerating the loose potassium sulfate / potassium magnesium sulfate powder into spheres, and converting free water into crystal water;

[0030] Step 4: Feed the granulated wet granules into a rotary dryer; control the inlet air temperature to 75-85℃ and the outlet temperature to 50-60℃; dry until the moisture content is ≤2.0%;

[0031] Step 5: Finally, the dried granules are screened by a vibrating screener to extract qualified granules with a particle size of 2.0-4.0mm; the qualified granules are cooled to below 40℃ in a fluidized bed cooler and packaged to obtain a synergistic potassium magnesium sulfate compound fertilizer.

[0032] Furthermore, in step 2, the amount of liquid sprayed is 8-12% of the total mass of the powder;

[0033] Furthermore, in step 5, if the fine powder smaller than 2mm is screened out, it is directly used as return material, and the large particles larger than 4mm are crushed by the crusher and used as return material, and then returned to step 2 for regranulation.

[0034] The beneficial effects of this invention are:

[0035] 1. This invention creatively introduces ammonium polyphosphate-modified magnesium oxide, utilizing the unique long-chain structure of ammonium polyphosphate as an ion lock to capture and chelate magnesium ions in situ at the fertilizer dissolution micro-interface, forming a complex with strong anti-interference ability. This form of magnesium can effectively avoid the competitive inhibition of root absorption channels by high concentrations of potassium ions, and under the same nutrient conditions, can significantly increase the chlorophyll content of crops, fundamentally solving the problem of antagonistic inhibition of magnesium absorption in traditional potassium-magnesium compound fertilizers;

[0036] 2. In the preparation method of the present invention, a dense and high-strength basic magnesium chloride whisker skeleton is grown in the interparticle gaps of potassium sulfate and potassium magnesium sulfate by using a magnesium chloride-citric acid composite solution to initiate a Sorel in-situ solidification reaction. This greatly improves the compressive strength of the fertilizer particles, solves the segregation problem that may occur during transportation, and converts the easily hygroscopic free water in the system into structurally stable crystal water. Combined with the hydrophobic effect of the ammonium polyphosphate modified layer, the moisture absorption weight gain rate is reduced to below 1.5%, completely overcoming the industry problem of easy moisture absorption and clumping of potassium magnesium sulfate fertilizers. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. The illustrative embodiments and descriptions of this invention are for explanation only and are not intended to limit the invention. Furthermore, regarding numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0038] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0039] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0040] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0041] Example 1

[0042] A synergistic potassium magnesium sulfate compound fertilizer, by weight, comprises the following raw materials: 200 parts potassium magnesium sulfate, 700 parts powdered potassium sulfate, 42 parts ammonium polyphosphate modified magnesium oxide, 18 parts potassium humate, and 85 parts magnesium chloride-citric acid compound solution.

[0043] The magnesium chloride-citric acid composite solution is a mixture prepared by dissolving 2.5% anhydrous citric acid in a 24% (w / w) magnesium chloride aqueous solution.

[0044] The pH value of the magnesium chloride-citric acid composite solution is controlled between 4.0 and 5.0;

[0045] The powdered potassium sulfate is agricultural-grade potassium sulfate produced by the Mannheim process and subjected to air jet milling, with a potassium oxide content ≥50% and a particle size distribution D90 ≤0.15mm; the moisture content of the powdered potassium sulfate is ≤0.5%.

[0046] The potassium magnesium sulfate is a double salt of magnesium sulfate monohydrate and potassium sulfate from natural pyromagnesia ore, with a magnesium oxide content ≥8% and a sulfur content ≥14%.

[0047] The potassium humate is: biochemical potassium humate, with a water-insoluble content ≤1.0% and a component proportion ≥70% of the components with a molecular weight distribution between 300-1000 Daltons.

[0048] The ammonium polyphosphate-modified magnesium oxide was prepared by the following method:

[0049] Step A: Take magnesium oxide and process it using an ultrafine pulverizer to make its particle size distribution D90≤20μm; place the powder in a high-speed mixer, add sodium dodecyl sulfate at 0.5% of the total mass of magnesium oxide, and mix at high speed of 1500-2000 rpm for 3-5 minutes to reduce the surface energy of the powder and prevent agglomeration using surfactants;

[0050] Step B: Add ammonium polyphosphate solution to a jacketed reactor, with a degree of polymerization n≥3 and P2O5 content≥30%; heat to 45-50℃, start stirring, add trace amounts of additives to adjust viscosity, and prepare a modified activation solution with high wettability;

[0051] Step C: Place the magnesium oxide powder treated in Step A into the fluidization chamber of the fluidized bed coating machine; turn on the induced draft fan to fluidize the powder, and control the inlet air temperature at 60±2℃; use a pressure atomizing spray gun with an orifice diameter of 0.5-0.8mm to uniformly spray the modified activating solution from Step B onto the surface of the magnesium oxide particles at a rate of 15-20ml / min; the spraying amount is 10-15% of the magnesium oxide mass.

[0052] Step D: After spraying, maintain the fluidized state and continue the reaction for 15-20 minutes, utilizing the polyphosphate ions in ammonium polyphosphate to react with the Mg on the MgO surface. 2+ Shallow chemical bonding occurs, forming a stable chelated film; then the temperature is raised to 80-85℃ for hot air drying until the moisture content is <1.0%, and then it is passed through a 100-mesh sieve to obtain ammonium polyphosphate surface-activated modified magnesium oxide.

[0053] The magnesium oxide pulverized in step A is lightly calcined magnesium oxide with an activity of 60-65.

[0054] The trace additive in step B is ethylene glycol, and the viscosity is adjusted to 150-200 cps.

[0055] A method for preparing a synergistic potassium magnesium sulfate compound fertilizer includes the following steps:

[0056] Step 1: Weigh out the ultrafine powdered potassium sulfate, potassium magnesium sulfate, ammonium polyphosphate surface-activated modified magnesium oxide, and potassium humate, and put them into a twin-shaft paddle mixer; mix for 8-10 minutes at a speed of 45-50 rpm, so that the modified magnesium oxide powder is evenly filled in the gaps between the potassium fertilizer and magnesium fertilizer particles, forming a dense microstructure.

[0057] Step 2: Continuously feed the mixture from Step 1 into the rotary drum granulator; start the granulator and control the rotation speed at 10-15 rpm; continuously spray the magnesium chloride-citric acid composite solution onto the material bed through a high-pressure atomizing nozzle, with the spray volume being 8-12% of the total powder mass;

[0058] Step 3: Control the material temperature in the granulator at 50-65℃, and use the exothermic reaction of magnesium chloride and magnesium oxide hydration and acid-base neutralization to spontaneously maintain the temperature; the material stays in the machine for 10-15 minutes; during this process, MgCl2 in the liquid phase and active MgO distributed in the solid phase, from ammonium polyphosphate modified magnesium oxide, rapidly undergo an in-situ reaction to generate needle-shaped basic magnesium chloride whiskers 5Mg(OH)2·MgCl2·8H2O, which strongly binds the loose potassium sulfate / potassium magnesium sulfate powder into spheres and converts free water into crystal water;

[0059] Step 4: Feed the granulated wet granules into a rotary dryer; control the inlet air temperature to 75-85℃ and the outlet temperature to 50-60℃; dry until the moisture content is ≤2.0%;

[0060] Step 5: Screening and post-processing: The dried granules are screened by a vibrating screener to extract qualified granules with a particle size of 2.0-4.0mm; the fine powder under the screen is directly used as return material, and the large granules on the screen are crushed by a crusher and used as return material, and returned to step 2 for re-granulation; the qualified granules are cooled to below 40℃ in a fluidized bed cooler, and after packaging, a synergistic potassium magnesium sulfate compound fertilizer is prepared.

[0061] Example 2

[0062] A synergistic potassium magnesium sulfate compound fertilizer, by weight, comprises the following raw materials: 235 parts potassium magnesium sulfate, 620 parts powdered potassium sulfate, 58 parts ammonium polyphosphate modified magnesium oxide, 12 parts potassium humate, and 115 parts magnesium chloride-citric acid compound solution.

[0063] The magnesium chloride-citric acid composite solution is a mixture prepared by dissolving 4.5% anhydrous citric acid in a 20% (w / w) magnesium chloride aqueous solution.

[0064] The preparation methods of ammonium polyphosphate modified magnesium oxide and the preparation method of a synergistic potassium sulfate magnesium compound fertilizer in Example 2 are the same as those in Example 1.

[0065] Example 3

[0066] A synergistic potassium magnesium sulfate compound fertilizer, by weight, comprises the following raw materials: 220 parts potassium magnesium sulfate, 660 parts powdered potassium sulfate, 50 parts ammonium polyphosphate modified magnesium oxide, 16 parts potassium humate, and 100 parts magnesium chloride-citric acid compound solution.

[0067] The magnesium chloride-citric acid composite solution is a mixture prepared by dissolving 3% anhydrous citric acid in a 22% magnesium chloride aqueous solution.

[0068] The preparation methods of ammonium polyphosphate modified magnesium oxide and the preparation method of a synergistic potassium sulfate magnesium compound fertilizer in Example 3 are the same as those in Example 1.

[0069] Example 4

[0070] A synergistic potassium magnesium sulfate compound fertilizer, by weight, comprises the following raw materials: 245 parts potassium magnesium sulfate, 640 parts powdered potassium sulfate, 45 parts ammonium polyphosphate modified magnesium oxide, 20 parts potassium humate, and 95 parts magnesium chloride-citric acid compound solution.

[0071] The magnesium chloride-citric acid composite solution is a mixture prepared by dissolving 3.5% anhydrous citric acid in a 25% (w / w) magnesium chloride aqueous solution.

[0072] The preparation methods of ammonium polyphosphate modified magnesium oxide and the preparation method of a synergistic potassium sulfate magnesium compound fertilizer in Example 4 are the same as those in Example 1.

[0073] Example 5

[0074] A synergistic potassium magnesium sulfate compound fertilizer, by weight, comprises the following raw materials: 250 parts potassium magnesium sulfate, 600 parts powdered potassium sulfate, 60 parts ammonium polyphosphate modified magnesium oxide, 10 parts potassium humate, and 120 parts magnesium chloride-citric acid compound solution.

[0075] The magnesium chloride-citric acid composite solution is a mixture prepared by dissolving 5% anhydrous citric acid in a 21% magnesium chloride aqueous solution.

[0076] The preparation methods of ammonium polyphosphate modified magnesium oxide and the preparation method of a synergistic potassium sulfate magnesium compound fertilizer in Example 5 are the same as those in Example 1.

[0077] Comparative Example 1

[0078] A synergistic potassium magnesium sulfate compound fertilizer, by weight, comprises the following raw materials: 220 parts potassium magnesium sulfate, 660 parts powdered potassium sulfate, 50 parts ammonium polyphosphate modified magnesium oxide, 16 parts potassium humate, and 100 parts magnesium chloride-citric acid compound solution.

[0079] The difference between this comparative example and Example 3 is that: in the preparation process of the ammonium polyphosphate modified magnesium oxide:

[0080] Steps A and C are omitted. Instead, the unmodified lightly calcined magnesium oxide powder is physically mixed with ammonium polyphosphate solution and then directly added to the raw materials for fertilizer granulation.

[0081] Apart from the above, the other components, their amounts, and preparation methods in this comparative example are the same as in Example 3.

[0082] Comparative Example 2

[0083] A synergistic potassium magnesium sulfate compound fertilizer, by weight, comprises the following raw materials: 220 parts potassium magnesium sulfate, 660 parts powdered potassium sulfate, 50 parts monoammonium phosphate modified magnesium oxide, 16 parts potassium humate, and 100 parts magnesium chloride-citric acid compound solution.

[0084] The difference between this comparative example and Example 3 is that in the preparation process of the modified magnesium oxide: in step 2, monoammonium phosphate solution is used to replace ammonium polyphosphate solution for coating the surface of magnesium oxide, thereby preparing monoammonium phosphate modified magnesium oxide, and replacing the ammonium polyphosphate modified magnesium oxide in Example 3.

[0085] Apart from the above, the other components, their amounts, and preparation methods in this comparative example are the same as in Example 3.

[0086] Comparative Example 3

[0087] A synergistic potassium magnesium sulfate compound fertilizer, by weight, comprises the following raw materials: 220 parts potassium magnesium sulfate, 660 parts powdered potassium sulfate, 50 parts ammonium polyphosphate modified magnesium oxide, 16 parts potassium humate, and 100 parts magnesium chloride-citric acid compound solution.

[0088] The difference between this comparative example and Example 3 is that: in the formulation of the magnesium chloride-citric acid composite solution, anhydrous citric acid is not added, and only a 25% magnesium chloride aqueous solution is used as the activating solution.

[0089] Apart from the above, the other components, their amounts, and preparation methods in this comparative example are the same as in Example 3.

[0090] Comparative Example 4

[0091] A synergistic potassium magnesium sulfate compound fertilizer, by weight, comprises the following raw materials: 220 parts potassium magnesium sulfate, 660 parts powdered potassium sulfate, 50 parts ammonium polyphosphate modified magnesium oxide, 16 parts potassium humate, and 100 parts magnesium chloride-citric acid compound solution.

[0092] The difference between this comparative example and Example 3 is that: in the formulation of the magnesium chloride-citric acid composite solution, the mass concentration of the magnesium chloride aqueous solution is adjusted to 10%; and anhydrous citric acid is maintained.

[0093] Apart from the above, the other components, their amounts, and preparation methods in this comparative example are the same as in Example 3.

[0094] Comparative Example 5

[0095] A synergistic potassium magnesium sulfate compound fertilizer, by weight, comprises the following raw materials: 220 parts potassium magnesium sulfate, 660 parts powdered potassium sulfate, 50 parts ammonium polyphosphate modified magnesium oxide, and 100 parts magnesium chloride-citric acid compound solution.

[0096] The difference between this comparative example and Example 3 is that the addition of potassium humate is omitted.

[0097] Apart from the above, the other components, their amounts, and preparation methods in this comparative example are the same as in Example 3.

[0098] Comparative Example 6

[0099] A synergistic potassium magnesium sulfate compound fertilizer, by weight, comprises the following raw materials: 220 parts potassium magnesium sulfate, 660 parts powdered potassium sulfate, 50 parts ammonium polyphosphate modified magnesium oxide, 48 parts potassium humate, and 100 parts magnesium chloride-citric acid compound solution.

[0100] The difference between this comparative example and Example 3 is that the amount of potassium humate added in the formulation is increased to 48 parts.

[0101] Apart from the above, the other components, their amounts, and preparation methods in this comparative example are the same as in Example 3.

[0102] Comparative Example 7

[0103] A synergistic potassium magnesium sulfate compound fertilizer, by weight, comprises the following raw materials: 220 parts potassium magnesium sulfate, 660 parts powdered potassium sulfate, 50 parts ammonium polyphosphate modified magnesium oxide, 16 parts potassium humate, and 100 parts magnesium chloride-citric acid compound solution.

[0104] The difference between this comparative example and Example 3 is that in step 4 of the preparation method of a synergistic potassium magnesium sulfate compound fertilizer, the drying temperature is increased and adjusted to 125°C.

[0105] Apart from the above, the other components, their amounts, and preparation methods in this comparative example are the same as in Example 3.

[0106] Comparative Example 8

[0107] A synergistic potassium magnesium sulfate compound fertilizer, by weight, has the following raw material composition: 220 parts potassium magnesium sulfate, 660 parts powdered potassium sulfate, and 70 parts conventional granulation binder bentonite.

[0108] The difference between this comparative example and Example 3 is that: the conventional granulating binder bentonite was used to replace the components such as ammonium polyphosphate surface-activated modified magnesium oxide and potassium humate in Example 3, so as to maintain the same total mass of solid phase, and only water was used.

[0109] In the preparation of compound fertilizer in Comparative Example 8, the weighed ultrafine powdered potassium sulfate, potassium magnesium sulfate, and conventional granulation binder bentonite were first added to a twin-shaft paddle mixer; the mixture was stirred for 8-10 minutes at a speed of 45-50 rpm; then the mixture was continuously fed into a rotary drum granulator; the granulator was started and the speed was controlled at 10-15 rpm; clean water was continuously sprayed onto the material bed through a high-pressure atomizing nozzle, with the spray volume being 8-12% of the total mass of the powder; the water was used to make the bentonite sticky, and the potassium magnesium powder was bound into spheres by physical agglomeration force.

[0110] Finally, the granulated wet granules are sent to a rotary dryer and dried until the moisture content is ≤2.0%. The dried granules are then screened by a vibrating screen to extract particles with a diameter of 2.0-4.0 mm, thus obtaining a synergistic potassium magnesium sulfate compound fertilizer as described in Comparative Example 8.

[0111] Test case

[0112] Compound fertilizer compressive strength test: Refer to the particle strength test method in GB / T21633-2020 "Blended Fertilizers"; randomly select 30 particles each from the examples and comparative examples, and use a particle strength tester to measure the force (Newtons, N) required to break each particle, and calculate the average value.

[0113] Test of abrasion resistance (pulverization rate) of compound fertilizer: Referring to the test method of fineness in GB / T20412-2021 "Calcium Magnesium Phosphate Fertilizer", a rotary abrasion tester was used. A certain amount of sample was weighed and placed in a drum with steel balls. After rotating for the same time, the mass percentage of powder produced was measured by sieving.

[0114] Hygroscopic weight gain test of compound fertilizer: Refer to the hygroscopicity determination method in the appendix of HG / T2843-2005 "Commonly Used Standard Titration Solutions, Standard Solutions, Reagent Solutions and Indicator Solutions for Chemical Analysis of Fertilizer Products"; place the quantitative samples of the examples and comparative examples in a constant temperature and humidity chamber; set the relative humidity of the chamber to 80% and the temperature to 30℃; after 24 hours, weigh again to determine the hygroscopic weight gain, and calculate the hygroscopic rate based on the initial weight.

[0115] Magnesium cumulative release rate of compound fertilizer: Static water immersion release rate test: Referring to GB / T23348-2009 "Slow-release Fertilizers", the samples of the examples and comparative examples were placed in static water at 25℃, and samples were taken at 1h, 24h, 3d, and 7d respectively. The Mg content in the solution was determined by inductively coupled plasma atomic emission spectrometry. 2+ The concentration of magnesium was determined, and then the cumulative release curve of magnesium was calculated, and the cumulative release rate of magnesium over 24 hours was obtained.

[0116] The test results are shown in Table 1:

[0117] Table 1

[0118]

[0119] As can be seen from the data in Table 1, the synergistic potassium magnesium sulfate compound fertilizers prepared in Examples 1-5 of this invention exhibit excellent comprehensive advantages in physical strength, moisture resistance, and nutrient release behavior, perfectly solving the problems of easy segregation and easy moisture absorption of existing potassium magnesium sulfate compound fertilizers.

[0120] Taking the optimal Example 3 as an example, its particle compressive strength is as high as 44.8N, far exceeding the 19.2N of the traditional Comparative Example 8 and 9.2N of Comparative Example 4; at the same time, its moisture absorption weight gain rate under 24-hour high temperature and high humidity conditions is only 1.3%, which is an order of magnitude lower than the 15.3% of Comparative Example 8; and its 24-hour magnesium cumulative release rate is controlled in the range of 36.2%, which is different from the explosive release of 84.3% of Comparative Example 2, and also avoids the rapid total dissolution of 97.8% shown by Comparative Example 8.

[0121] This invention constructs a dense inorganic crystal framework through the Sorel reaction. The difference between Comparative Examples 3 and 4 and Example 3 is that the mass concentration of magnesium chloride aqueous solution in one example is adjusted to 10%, and anhydrous citric acid is not added in the other example. The particle compressive strength data of Comparative Examples 3 and 4 collapsed to 11.9N and 9.2N respectively, even lower than that of the physical blending group, which fully proves that the magnesium chloride-citric acid composite solution defined in this application is not a simple binder, but the key to precisely controlling the growth of Mg(OH)2⋅MgCl2⋅8H2O whiskers. Only within a specific acidity and concentration range can a strong exothermic reaction be induced and a high-strength crystalline phase be generated, thereby firmly locking potassium sulfate and potassium magnesium sulfate powder like reinforced concrete, eliminating the segregation risk that may occur during transportation.

[0122] The difference between Example 7 and Example 3 is that in step 4 of the preparation method of a synergistic potassium magnesium sulfate compound fertilizer, the drying temperature is increased to 125°C; this results in a higher moisture absorption rate of 7.9%. The possible reason is that the high temperature of 125°C will destroy the crystal water structure of magnesium cement, causing the crystal skeleton to collapse and release free moisture absorption sites.

[0123] In embodiments 1-5 of the present invention, the free water in the system is converted into stable chemical crystal water through low-temperature curing, and a hydrophobic modified layer formed by ammonium polyphosphate modified magnesium oxide is constructed from the inside out to form a double moisture barrier.

[0124] Comparative Example 2 used monoammonium phosphate to replace ammonium polyphosphate, and its magnesium release rate was as high as 84.3%, completely losing the slow-release characteristic. This fully demonstrates that the technical solution of this application, by modifying magnesium oxide with ammonium polyphosphate, can form an ion lock in the fertilizer micro-interface, and slowly release magnesium in a complexed state, thereby avoiding the explosive dissolution of magnesium ions at the moment of water entry, and laying a chemical basis for solving the potassium-magnesium antagonism in the rhizosphere.

[0125] Furthermore, Example 6 used an excessive amount of potassium humate, and its particle compressive strength of 17.8 N and moisture absorption rate of 5.2% were both inferior to those of Example 3. The possible reason is that if there are excessive organic macromolecules, the continuity of the inorganic crystal skeleton will be blocked. This fully demonstrates that the component ratio screening of the technical solution of this application is necessary and inventive.

[0126] Potted plant comprehensive test: The potted plant test was conducted in accordance with NY / T496-2002 "General Rules for Rational Use of Fertilizers". A tomato variety named Jinpeng No. 1 that is sensitive to potassium and magnesium antagonism was selected. The potted plants were grown in acidic red soil with a medium to low effective magnesium content, and the effective magnesium content in the soil was controlled to be <50mg / kg.

[0127] The blank control was treated with clean water throughout the entire process. Except for the blank control, the total amount of N, P, K and Mg applied in the other examples and comparative examples was completely consistent; and all other management methods and conditions were consistent.

[0128] 45 days after transplanting, cut the plant at ground level and divide it into stem and leaf parts. Wash the fresh sample with deionized water, blanch at 105℃ for 30 minutes, and dry at 80℃ to constant weight. Weigh the total dry weight of the above-ground parts, which is the dry weight of the plant.

[0129] Leaf chlorophyll content (SPAD value) was measured using the fourth leaf from the bottom of the tomato plant and a SPAD-502Plus portable chlorophyll meter. During the measurement, six points were randomly measured on each leaf, avoiding the veins, and the average value was taken.

[0130] The comprehensive test results are shown in Table 2:

[0131] Table 2

[0132]

[0133] As can be seen from the data in Table 2, under the premise of the same nutrient input, the plant dry weight and leaf chlorophyll (SPAD value) values ​​of Example 3 of the present invention are significantly better than those of all control groups.

[0134] The dry weight of plants in Example 3 reached 49.1 g / plant, and the chlorophyll SPAD value of leaves was as high as 53.4, which was 60.5% and 60.8% higher than that of Comparative Example 8, respectively. This fully demonstrates that under the traditional physical mixing mode, although sufficient magnesium was applied, the crop was actually in a state of latent magnesium deficiency due to the strong antagonism of potassium ions. The chlorophyll SPAD value of leaves in Comparative Example 8 was only 33.2, close to the level of nutrient deficiency. However, the technical solution of the present invention truly achieves effective absorption of magnesium.

[0135] The chlorophyll SPAD value of leaves in Comparative Example 2 was only 34.5, which was not much different from that in Comparative Example 8, indicating that the simple mixing of phosphorus and magnesium could not solve the antagonistic problem. The high chlorophyll SPAD value of leaves presented in Example 3 of the present application may be due to the fact that the magnesium released by polyphosphate is chelated into an electrically neutral or negatively charged complex, which changes the form of magnesium in the rhizosphere. This prevents magnesium from passing through the ion channels inhibited by potassium ions, but instead allows it to be actively taken up by the plant through the complexed channels. This cleverly avoids the antagonistic mechanism and directly supplies the core of chlorophyll synthesis, achieving the physiological synergistic effect of potassium and magnesium supplementation.

[0136] Although the dry weight of Comparative Example 5 was 41.3 g and the SPAD value of leaf chlorophyll was better than that of physical blending, it was still significantly lower than that of Example 3. This indicates that potassium humate in this system is not only a nutrient component, but also plays an auxiliary role in the transport of organic bridging components, further enhancing the migration of magnesium complexes in the soil and root affinity, demonstrating the synergistic effect between the formulation components of the technical solution of this application.

[0137] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A synergistic potassium magnesium sulfate compound fertilizer, characterized in that, The composition, by weight, is as follows: 200-250 parts potassium magnesium sulfate, 600-700 parts powdered potassium sulfate, 40-60 parts ammonium polyphosphate modified magnesium oxide, 10-20 parts potassium humate, and 80-120 parts magnesium chloride-citric acid composite solution; the magnesium chloride-citric acid composite solution is a mixture prepared by dissolving 2%-5% anhydrous citric acid in a 20%-25% magnesium chloride aqueous solution, with a pH of 4.0-5.0; the ammonium polyphosphate modified magnesium oxide is prepared by the following method: Step A: Take magnesium oxide and process it using an ultrafine pulverizer to make its particle size distribution D90≤20μm; place the powder in a high-speed mixer, add sodium dodecyl sulfate, and mix at high speed of 1500-2000 rpm for 3-5 minutes to reduce the surface energy of the powder and prevent agglomeration using surfactants; Step A: Step B: Add ammonium polyphosphate solution to a jacketed reactor; heat to 45℃-50℃, start stirring, add trace amounts of additives to adjust viscosity, and prepare a modified activation liquid with high wettability; Step C: Place the magnesium oxide powder treated in Step A into the fluidization chamber of a fluidized bed coating machine; turn on the induced draft fan to keep the powder in a fluidized state, and control the inlet air temperature at 60±2℃; use a pressure atomizing spray gun to uniformly spray the modified activation liquid from Step B onto the surface of magnesium oxide particles at a rate of 15-20 ml / min; the spraying amount is 10%-15% of the magnesium oxide mass; Step D: After spraying, maintain the fluidized state and continue the reaction for 15-20 minutes to form a stable chelated film; then heat to 80-85℃ for hot air drying until the moisture content is <1.0%, and pass through a 100-mesh sieve to obtain ammonium polyphosphate surface-activated modified magnesium oxide.

2. The synergistic potassium magnesium sulfate compound fertilizer according to claim 1, characterized in that, The synergistic potassium magnesium sulfate compound fertilizer comprises, by weight, the following components: 220 parts potassium magnesium sulfate, 660 parts powdered potassium sulfate, 50 parts ammonium polyphosphate modified magnesium oxide, 16 parts potassium humate, and 100 parts magnesium chloride-citric acid compound solution.

3. The synergistic potassium magnesium sulfate compound fertilizer according to claim 1, characterized in that, The moisture content of the powdered potassium sulfate is ≤0.5%.

4. The synergistic potassium magnesium sulfate compound fertilizer according to claim 1, characterized in that, The powdered potassium sulfate is agricultural grade potassium sulfate produced by the Mannheim process and treated by air jet milling, with a potassium oxide content ≥50% and a particle size distribution D90 ≤0.15mm.

5. A synergistic potassium magnesium sulfate compound fertilizer according to claim 1, characterized in that, The potassium magnesium sulfate is a double salt of magnesium sulfate monohydrate and potassium sulfate from natural soft potassium magnesium alum ore, with a magnesium oxide content of ≥8% and a sulfur content of ≥14%.

6. A synergistic potassium magnesium sulfate compound fertilizer according to claim 1, characterized in that, The potassium humate is: biochemical potassium humate, with a water-insoluble content ≤1.0% and a component proportion ≥70% of the components with a molecular weight distribution between 300-1000 Daltons.

7. A synergistic potassium magnesium sulfate compound fertilizer according to claim 1, characterized in that, The magnesium oxide being pulverized in step A is lightly calcined magnesium oxide with an activity of 60-65.

8. A synergistic potassium magnesium sulfate compound fertilizer according to claim 1, characterized in that, The mass of sodium dodecyl sulfate added in step A is 0.5% of the total mass of magnesium oxide.

9. A synergistic potassium magnesium sulfate compound fertilizer according to claim 1, characterized in that, The ammonium polyphosphate solution added in step B has a degree of polymerization n≥3 and a P2O5 content≥30%.

10. A synergistic potassium magnesium sulfate compound fertilizer according to claim 1, characterized in that, The trace additive in step B is ethylene glycol, and the viscosity is adjusted to 150cps-200cps.

11. A method for preparing a synergistic potassium magnesium sulfate compound fertilizer according to any one of claims 1-10, characterized in that, The preparation method includes the following steps: Step 1: Weighed powdered potassium sulfate, potassium magnesium sulfate, ammonium polyphosphate modified magnesium oxide, and potassium humate are added to a twin-shaft paddle mixer; at a speed of 45-50 rpm, the mixture is mixed for 8-10 minutes to ensure that the modified magnesium oxide powder is evenly filled in the gaps between the potassium fertilizer and magnesium fertilizer particles, forming a dense microstructure; Step 2: The mixture from Step 1 is continuously fed into a rotary drum granulator; the granulator is started, and the speed is controlled at 10-15 rpm; a magnesium chloride-citric acid composite solution is continuously sprayed onto the material bed through an atomizing nozzle; Step 3: The material temperature inside the granulator is controlled at 50℃-65℃, and the material residence time inside the machine is 10-15 minutes. Minutes; During this process, MgCl2 in the magnesium chloride-citric acid composite solution reacts rapidly with the active MgO in the ammonium polyphosphate modified magnesium oxide, strongly binding the loose potassium sulfate / potassium magnesium sulfate powder into spheres and converting free water into crystal water; Step 4: The granulated wet granules are sent to a rotary dryer; the inlet air temperature is controlled at 75℃-85℃ and the outlet temperature at 50℃-60℃; dried until the moisture content is ≤2.0%; Step 5: Finally, the dried granules are screened by a vibrating screener to extract qualified granules with a particle size of 2.0mm-4.0mm; the qualified granules are cooled to below 40℃ in a fluidized bed cooler, and after packaging, a synergistic potassium magnesium sulfate compound fertilizer is obtained.

12. The preparation method according to claim 11, characterized in that, In step 2 of the preparation method of the synergistic potassium magnesium sulfate compound fertilizer, the amount of liquid sprayed by the atomizing nozzle is 8%-12% of the total mass of the powder.

13. The preparation method according to claim 11, characterized in that, In step 5 of the method for preparing a synergistic potassium magnesium sulfate compound fertilizer, fine powder smaller than 2mm is directly used as return material, while large particles larger than 4mm are crushed by a crusher and used as return material, and then returned to step 2 for regranulation.

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