Nitrogen-containing polyhalite particles

Abstract

The invention provides a method for preparing polyhalite particles. The method comprises the following steps: providing an ammonium nitrate (AN) aqueous solution; heating the solution to produce a hot solution; adding the hot solution into polyhalite; and allowing the mixture to cool during the granulation process. The invention also provides a method of making polyhalite particles wherein the polyhalite is granulated with ammonium nitrate to form potassium nitrate, calcium ammonium nitrate, ammonium nitrate and / or magnesium nitrate and ammonium sulfate, as well as polyhalite particles comprising polyhalite and potassium ammonium nitrate.

Description

Technical Field

[0001] The present invention relates to kainite particles and a method for preparing the same. The kainite particles include kainite and ammonium nitrate, and are manufactured by using a hot ammonium nitrate solution method. Background Art

[0002] For normal growth, plants require nutrients (nitrogen, phosphorus, potassium, calcium, zinc, magnesium, iron, manganese, etc.), which can usually be found in the soil. Sometimes fertilizers are needed to achieve the desired plant growth because these fertilizers can promote plant growth.

[0003] Plant growth is satisfied in two ways. The traditional way is to provide nutritional additives. Another way some fertilizers act is by improving the effectiveness of the soil by changing its water retention and aeration. Fertilizers usually provide three main macronutrients in different proportions, namely

[0004] · Nitrogen (N),

[0005] · Phosphorus (P), and

[0006] · Potassium (K),

[0007] And three secondary macronutrients, namely

[0008] · Calcium (Ca),

[0009] · Magnesium (Mg), and

[0010] · Sulfur (S).

[0011] In addition, micronutrients such as copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo), zinc (Zn), boron (B), etc. are usually included. Occasionally, there are silicon (Si), cobalt (Co), vanadium (V), and some rare mineral catalysts.

[0012] The most reliable and effective way to match the availability of nutrients with plant needs is to match the solution released into the soil with the plant's needs, usually using slow-release or controlled-release fertilizers.

[0013] Although both slow-release fertilizers (SRF) and controlled-release fertilizers (CRF) gradually provide nutrients, they differ in many aspects, including the technologies they use, release mechanisms, lifetimes, release control factors, etc.

[0014] Solid fertilizers include granules, pellets, crystals, and powders. Among these products, granules are preferred and have been widely used because they can be more easily applied by spreading on the soil surface and can release nutrients into the root zone over time during crop development.

[0015] Polyhalite is an evaporite mineral, a hydrated sulfate of potassium, calcium, and magnesium with the chemical formula: K2Ca2Mg(SO4)4·2H2O. Polyhalite is used as a fertilizer because it contains four important macronutrients.

[0016] Common processes for making granules include:

[0017] · Wet granulation: Using a liquid or solution containing a binder to promote agglomeration, and then drying and screening the product.

[0018] · Dry granulation: Using a binder and / or pressure to produce granules without adding any liquid, such as using compaction or extrusion. Subsequently, the granules can be ground, scraped, or screened to achieve the desired particle size distribution.

[0019] · Hot melt granulation: A subdivision of wet granulation, where the binder is melted to promote nucleation. This route allows for higher productivity due to increased granulation efficiency and a significant reduction in dryer capacity requirements (dryer capacity can be a bottleneck for many granulation plants).

[0020] There is a need for a granulation method that addresses several drawbacks known in the art, including using less water, reducing energy requirements, and increasing granulation efficiency. Summary of the Invention

[0021] According to a first aspect of the present invention, there is provided a method for preparing polyhalite granules, comprising the following steps:

[0022] a) Providing an aqueous solution of ammonium nitrate (AN);

[0023] b) Heating the solution to produce a hot solution;

[0024] c) Adding the hot solution to polyhalite;

[0025] d) Allowing the mixture to cool during the granulation process.

[0026] The polyhalite granules can contain ammonia and / or nitrogen in nitrogen-related forms.

[0027] Ammonium nitrate (AN) is a compound with the chemical formula NH4NO3. AN accounts for more than 15% of the global nitrogen fertilizer demand. It is a white crystalline salt composed of ammonium ions and nitrate ions. It is highly soluble in water, is hygroscopic as a solid, but does not form hydrates.

[0028] Although AN is not as nitrogen-rich as urea in terms of nitrogen content, and urea is also cheaper, AN is more suitable because it contains nitrogen in the form of ammonia and nitrate (required by plants), unlike the urease in urea. This property ensures less ammonia and N2O loss compared to the loss of urease to the atmosphere.

[0029] The AN aqueous solution can be of any concentration, but is preferably concentrated to more than 90% by weight of AN, more preferably between about 91.3 and 98.3%, and most preferably about 92% by weight of AN (w / w).

[0030] The AN solution is heated to increase the solubility of AN in water and then granulated with polyhalite. This mixture provides additional nutrients such as potassium, sulfur, calcium, and magnesium to the final product, while extending the temperature of the AN transition phase to improve the safety of the product during processing and storage.

[0031] The hot AN solution can be added to polyhalite in a weight ratio of about 50:50 to about 95:05, more preferably about 60:40, and most preferably about 65:35 (AN solution: polyhalite).

[0032] The AN solution is preferably heated to a temperature of at least 100 degrees Celsius, preferably between about 126 and about 160 degrees Celsius (°C), and more preferably between about 145 and about 150 degrees Celsius.

[0033] The method can include the step of coating the particles with a combination of oil / wax and / or talc to prevent moisture absorption, caking, and dust generation.

[0034] The method according to the present invention can include the step of physically sizing the polyhalite particles, wherein the particles that are too large and too small are fed into a recirculation loop.

[0035] Polyhalite can be combined with a potassium fertilizer source (such as potassium chloride, potassium nitrate, kainite, and / or potassium sulfate and / or other potassium-containing minerals / substances).

[0036] The polyhalite particles can also contain boron, ulexite, tincalconite, or any combination thereof, and / or zinc oxide or zinc sulfate and molybdenum (such as ammonium molybdate or sodium molybdate dihydrate). In one embodiment, boron, ulexite, tincalconite, or any combination thereof, and / or zinc oxide or zinc sulfate and molybdenum (such as ammonium molybdate or sodium molybdate dihydrate) can be added to the polyhalite and / or the polyhalite hot AN mixture.

[0037] Boron can be present in an amount of 0.1% (w / w) to 1.0% (w / w), preferably 0.2% (w / w) to 0.8% (w / w), and even more preferably 0.3% (w / w) to 0.5% (w / w).

[0038] Zinc can be present in an amount of 0.1% (w / w) to 1.0% (w / w), preferably 0.1% (w / w) to 0.5% (w / w), and even more preferably 0.1% (w / w) to 0.3% (w / w).

[0039] The particle size range of the polyhalite particles prepared according to the present invention can generally be from about 1.0 mm to about 6.0 mm, preferably from 2.0 mm to 4.0 mm, and even more preferably from 2.7 mm to 3.1 mm.

[0040] The average particle size of the polyhalite particles can be from about 1 mm to about 3.5 mm, preferably from 2 mm to 2.4 mm, preferably from 2.5 mm to 3.5 mm, preferably from 2.6 mm to 3.1 mm, and even more preferably from 2.7 mm to 2.8 mm.

[0041] The granulation process can be carried out using a granulator selected from drum granulators, but different equipment can be used, such as disk granulators, granulation towers, intensive mixers such as Eirich (registered trademark) intensive mixers, high shear machines, fluidized beds, hot and cold spheronizers, or any other type of equipment or combination capable of producing particles.

[0042] The method according to the present invention may also include using a dryer. The dryer conditions will depend on the AN:polyhalite ratio. For the claimed range (AN weight between 50 and 95%), the inlet temperature should be about 150 to 300 degrees Celsius, more preferably in the range of about 150 to 275 degrees Celsius, even more preferably in the range of about 150 to 200 degrees Celsius, and should not be higher than about 300 degrees Celsius to avoid the decomposition of ammonium nitrate. The outlet temperature of the gas can be up to 125 degrees Celsius, but is preferably about 90 to 100 degrees Celsius.

[0043] The pH value of the granulator can be controlled and can be higher than about 4.5, and even more preferably higher than about 5.0.

[0044] The method according to the present invention can follow a traditional drum granulation process, in which solid polyhalite powder and recycle are fed into a drum granulator. The hot AN solution can be fed into the granulator through a sprayer.

[0045] According to a second aspect of the present invention, there is provided a polyhalite particle comprising potassium ammonium nitrate. (Nitramite or Gwihabaite is the mineralogical name of (NH4,K)NO3). The particles can contain at least 10% w / w, 20% w / w, 30% w / w, 40% w / w or 50% w / w of potassium ammonium nitrate. The particles can be produced by the method according to the present invention.

[0046] The particles can also contain potassium nitrate, calcium ammonium nitrate, ammonium nitrate and / or magnesium nitrate.

[0047] The polyhalite particles can contain ammonia and / or nitrogen in a nitrogen-related form.

[0048] According to a third aspect of the present invention, there is provided a method for preparing polyhalite particles, wherein polyhalite is granulated with ammonium nitrate to form potassium nitrate, calcium ammonium nitrate, ammonium nitrate and / or magnesium nitrate.

[0049] Description of preferred embodiments

[0050] The present invention aims to provide an alternative to the method of agglomeration by binding of mineral particles using a binder, and uses the solidification of particles in a hot AN solution and mineral polyhalite mixture during the granulation process (such as a drum granulation process).

[0051] The present invention uses a hot ammonium nitrate (AN) solution enriched with 92% to 98% by weight of AN to bind polyhalite powder and / or particles together. The use of AN in the present invention is achieved through solidification / crystallization during the cooling of the hot material in the granulation process, and the heat of crystallization is used to evaporate the water in the AN solution and the water added to promote granulation due to correct gas flow conditions within the pelletizer.

[0052] Without being bound by theory, the applicant believes that polyhalite provides a solid bed in which the AN solution will crystallize upon cooling. At 105 to 108 degrees Celsius, AN will begin to crystallize / solidify, while polyhalite will provide Mg, K, S, and Ca, which can react with AN and act like additives, thereby changing the AN crystallization curve and providing stability against thermal decomposition.

[0053] In one embodiment of the present invention, a ratio of 65% by weight AN: 35% by weight polyhalite is used.

[0054] Without being bound by theory, the applicant believes that this method may result in the formation of other nitrates in the particles, such as potassium ammonium nitrate, potassium nitrate, magnesium nitrate, calcium nitrate, and calcium ammonium nitrate (CAN), as well as ammonium sulfate, through chemical reactions occurring during the process.

[0055] The granulation of ammonium nitrate and polyhalite can be understood as a combination of wet and melt granulation, where ammonium nitrate does not melt, but the aqueous solution is heated to further increase the solubility of AN in water, thereby producing a hot solution with 92 to 98% (w / w) AN. Therefore, less water is required for granulation than in wet granulation. This characteristic, combined with the heat released by AN crystallization, greatly reduces the energy requirement for drying the product to the required moisture range (less than 0.3%).

[0056] Some advantages of the method according to the present invention include:

[0057] - The hot ammonium nitrate solution is used as the liquid phase to promote the nucleation of powdered polyhalite.

[0058] - Provide a solid bed where ammonium nitrate will crystallize during the phase change process, which will start to occur when the bed temperature drops to about 105 to 108 degrees Celsius.

[0059] - Polyhalite provides other nutrients (such as magnesium, potassium, calcium, and sulfur) for the final product.

[0060] - Other nutrients act like additives to ammonium nitrate, providing higher stability and increasing the temperature at which the phase change occurs.

[0061] - Other nutrients stabilize the phase temperature of the AN crystallization curve (which occurs at about 32 degrees Celsius). This results in less decomposition of the granules due to thermal cycling during long-term storage. Description of the Drawings

[0062] Figure 1 is a schematic diagram of the mass balance of the method according to the present invention.

[0063] Figure 2 is a schematic diagram of the method according to the present invention.

[0064] Figure 3 is a photograph of uncoated granules of ammonium nitrate and polyhalite (65:35 w / w) according to the present invention.

[0065] Figure 4 is a photograph of coated granules of ammonium nitrate and polyhalite (65:35 w / w) according to the present invention.

[0066] Figure 5 is a graph of dust generation over time.

[0067] Figure 6 is a graph of wear rate over time.

[0068] Figure 7 is a graph of water absorption at different temperatures. Detailed Description of the Invention

[0069] In Figure 1 and Figure 2 a conventional granulation process 10 is shown, where fertilizer granules 21 containing N, K, S, Mg, and Ca are produced using a drum granulator 13. Polyhalite powder 11 is supplied to the drum granulator 13 at a certain content (kg / h) to achieve the required potassium concentration in the final product. At this stage, other powders such as potassium chloride, magnesium oxide, kainite, ammonium sulfate, and / or ulexite can also be added. Ammonium nitrate solution 12 is added to the granulator 13 using a sprayer. As the temperature of the solid surface drops, ammonium nitrate will start to crystallize, and granules will be produced and grow. Water is added to the granulator 13 to control the liquid phase. The pH value is controlled above 4.5, and if the pH value starts to drop, ammonia can be added at a ratio of about 2 to 3 kg / t.

[0070] The granulation emissions enter the dryer 14, where the granules will be dried to a maximum moisture content of 0.5%. After that, the polyhalite and ammonium nitrate granules are classified (by using the screening section 15) into the desired particle sizes, and the fines are directed back to the granulator. The coarse granules are ground by the grinder 16 and mixed with the fine powder to form a recycle, which feeds the granulator 13. The granules meeting the desired size pass through the cooler 17 and then enter the polishing / coating drum 20, where (optionally) talc (to prevent caking) 19 and oil (to prevent dust generation) 18 are added to coat the granules. The product 21 leaving the cooler 17 should be below 45 degrees Celsius, or at least about 20 degrees Celsius lower than room temperature.

[0071] Example 1

[0072] A 65 wt% ammonium nitrate solution is pumped into a drum granulator in the presence of powdered polyhalite and recycle material. Powdered polyhalite is added at a ratio of 35 wt%, while maintaining the recycle rate at 5.0. The final product contains 0.18% moisture, 21.9% nitrogen, 5.0% potassium (K2O), 2.15% magnesium oxide, and 7.35% sulfur (in the form of sulfate). The average compressive strength is 8.7 kgf, and the product particle size distribution is 98% between 2 and 5 mm. The product is as Figure 3 shown. After cooling, powder and oil are added to coat the final product to reduce the caking tendency and dust generation, as Figure 4 shown. This batch is named polyhalite granules containing ammonium nitrate (PGAN) "Batch A".

[0073] The above process is repeated to produce a second batch of granules named PGAN "Batch B".

[0074] Batch A of PGAN is prepared at 100% relative humidity compared to Batch B of PGAN prepared under drier and warmer conditions.

[0075] Batch B of PGAN has the following characteristics:

[0076] Nutritional components Batch B Total nitrogen (%) 22.0 Ammoniacal nitrogen (%) 11.6 Nitrogen-related form nitrogen (%) 10.4 <![CDATA[Potassium in the form of K2O (%)]]> 4.6 <![CDATA[Water-soluble K2O (%)]]> 4.4 Magnesium oxide (%) 2.3 Water-soluble magnesium oxide (%) 2.2 Sulfur (%) 6.9 <![CDATA[SO3 (%)]]> 17.6 <![CDATA[Water-soluble SO3 (%)]]> 17.0 CaO (%) 6.0 Water-soluble CaO (%) 3.6

[0077] Table 1 Nutritional Components (% wt.)

[0078]

[0079]

[0080] Table 2 Physical Properties

[0081]

[0082] Table 3 Size Guide Number (SGN) and Uniformity Index (UI) Physical Properties

[0083] The Size Guide Number (SGN) is the average (not median) particle size multiplied by 100.

[0084] The Uniformity Index (UI) is an indication of particle size uniformity. A range of 40 to 60 is considered uniform.

[0085] Calculated as d95 / d10 × 100.

[0086]

[0087]

[0088] Table 4 Moisture Penetration

[0089] CPG is a Conventional Polyhalite Granule (“CPG”) containing 99.2% w / w polyhalite and 0.8% w / w corn starch.

[0090]

[0091] Table 5 Caking Test Results

[0092] * Bag Hardness - After removing the “false” weights, the test bag is inspected without moving it from its original position. The inspector “feels” each bag and records the bag group as none, light, medium, or hard.

[0093] * % Caking - % of +12.5 mm lumps. The test bag is dropped from a height of 1 m twice and then very carefully screened.

[0094] * Caking Hardness - Assessed by crushing in the hand. Light ones break easily. Medium ones may break when pressed against a hard surface. Hard ones cannot be broken without mechanical means.

[0095]

[0096] Table 6 Chemical Evaluation

[0097]

[0098] Table 7 Quantitative Phase Analysis of XRPD Data for Different Samples of Batch B Using the Rietveld Method

[0099] (wt.%)

[0100] In Table 7:

[0101] nd = not detected

[0102] SV = sylvite

[0103] PHL = polyhalite

[0104] HL = halite

[0105] AHD = anhydrite MAG = magnesite UR = urea GLB = glauberite PAN = potassium ammonium nitrate (gwihabate-K)

[0106] AC = ammonium chloride (salammoniac)

[0107] SN = sodium nitrate ((soda niter)

[0108] ANS = ammonium nitrate sulfate AMSH = ammonium magnesium sulfate hydrate (ammonium magnesite)

[0109] Figure 5 The change in dust generation over time for Batch A and Batch B is shown.

[0110] Figure 6 The change in wear rate over time for Batch A and Batch B is shown.

[0111] Figure 7 The water absorption of Batch B at different temperatures is shown.

Claims

1. A method for preparing polyhalite particles, comprising the following steps: a) Providing an aqueous ammonium nitrate (AN) solution; b) Heating the solution to produce a hot solution; c) Adding the hot solution to polyhalite; and d) Allowing the mixture to cool during the granulation process.

2. The method according to claim 1, wherein the AN aqueous solution is concentrated to more than 80 wt% AN.

3. The method according to claim 1 or 2, wherein the AN aqueous solution is concentrated to about 92 wt% AN.

4. The method according to any one of the preceding claims, wherein the hot solution is added to a bed of polyhalite powder and / or particles.

5. The method according to any one of the preceding claims, wherein the hot AN solution is added to the polyhalite in a weight ratio of 50:50 to 95:05 (AN solution: polyhalite).

6. The method according to any one of the preceding claims, wherein the hot AN solution is heated to a temperature of 126 to 160 degrees Celsius (°C).

7. The method according to any one of the preceding claims, wherein the method further comprises a step of coating the particles with a combination of oil / wax and / or talc to prevent moisture absorption, caking and / or dust generation.

8. The method according to any one of the preceding claims, wherein the method further comprises a step of physically sizing the polyhalite particles, wherein the oversized and undersized particles are fed into a recycle loop.

9. The method according to any one of the preceding claims, wherein the method utilizes a granulator selected from a drum granulator, a pan granulator, a granulation tower, a high-intensity mixer, a high-shear machine, a hot and cold spheronizer, a fluidized bed or any other type of equipment or combination of equipment capable of producing particles.

10. The method according to any one of the preceding claims, wherein the polyhalite is combined with another potassium source, the potassium source comprising potassium nitrate, kainite and / or potassium sulfate and / or other potassium-containing minerals / substances.

11. The method according to any one of the preceding claims, wherein boron, ulexite, borax or any combination thereof and / or zinc oxide or zinc sulfate and molybdenum (as ammonium molybdate or sodium molybdate dihydrate) is added to the polyhalite and / or the polyhalite hot AN mixture.

12. The method according to any one of the preceding claims, wherein the particle size of the particles ranges from 1.0 mm to 6.0 mm.

13. The method according to any one of the preceding claims, wherein the method further comprises a step of drying the particles using a dryer.

14. The method according to claim 14, wherein the drying conditions are not higher than about 300 degrees Celsius.

15. A method for preparing polyhalite particles, wherein polyhalite is granulated with ammonium nitrate to form potassium nitrate, calcium ammonium nitrate, ammonium nitrate and / or magnesium nitrate and ammonium sulfate.

16. A polyhalite particle comprising polyhalite and potassium ammonium nitrate.

17. The polyhalite particle according to claim 16, comprising at least 10% w / w, 20% w / w, 30% w / w, 40% w / w or 50% w / w of potassium ammonium nitrate.

18. The polyhalite particle according to claim 16 or 17, prepared by the method according to any one of claims 1 to 15.

19. The polyhalite particles according to any one of claims 16 to 18, wherein the particles further comprise potassium nitrate, calcium ammonium nitrate, ammonium nitrate and / or magnesium nitrate.

20. The polyhalite particles according to any one of claims 16 to 19, wherein the particles comprise ammonia and / or nitrogen in a nitrogen-related form.

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