Nitrogen-containing polyhalite granules

Abstract

The present invention provides a process for preparing polyhalite granules, comprising the steps of providing an aqueous ammonium nitrate (AN) solution, heating the solution to form a hot solution, adding the hot solution to polyhalite, and cooling the mixture during the granulation process. The present invention further provides a process for preparing polyhalite granules, in which 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 granules comprising polyhalite and potassium ammonium nitrate.

Description

[Technical Field]

[0001] Introduction The present invention relates to polyhalite granules and a process for their manufacture. The polyhalite granules comprise polyhalite and ammonium nitrate and are manufactured in a process utilizing a hot ammonium nitrate solution. [Background technology]

[0002] Background of the Invention Plants require nutrients that can usually be found in the soil (nitrogen, phosphorus, potassium, calcium, zinc, magnesium, iron, manganese, etc.) to grow properly. Sometimes fertilizers are needed to achieve desired plant growth, as they can promote plant growth.

[0003] This growth of plants is met in two ways, the traditional one is additives that provide nutrients. The second action of some fertilizers is to increase their effectiveness by improving the water retention and aeration of the soil. Fertilizers typically contain, in various proportions, three major macronutrients: Nitrogen (N), Phosphorus (P), and Potassium (K), as well as three secondary macronutrients, viz. Calcium (Ca), Magnesium (Mg), and Sulfur (S) to provide.

[0004] Additionally, micronutrients such as copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo), zinc (Zn), and boron (B) are also often present. Of occasional importance are silicon (Si), cobalt (Co), and vanadium (V), as well as some rare mineral catalysts.

[0005] The most reliable and effective way to match nutrient availability with plant needs is to match their release into the soil solution to plant needs, typically by using sustained- or controlled-release fertilizers.

[0006] Both sustained-release fertilizers (SRF) and controlled-release fertilizers (CRF) deliver nutrients gradually, but they differ in many ways, including the technology they use, the release mechanism, lifespan, and release-controlling factors.

[0007] Solid fertilizers include granules, pellets, crystals, and powders. Of these products, granules are preferred and widely used because they can be more easily applied by scattering on the soil surface and release nutrients to the root zone over time as the crop grows.

[0008] Polyhalite is an evaporite mineral, a hydrated sulfate of potassium, calcium, and magnesium with the formula KCaMg(SO)H0. Polyhalite is used as a fertilizer because it contains four of the important macronutrients.

[0009] Commonly known processes for making granules are: Wet granulation: A liquid or solution containing a binder is used to promote agglomeration, followed by drying and sieving of the product. Dry granulation: Granules are produced without any liquid addition using binders and / or pressure, e.g., by compaction or extrusion. The particles may subsequently be milled, ground or sieved to reach the desired particle size distribution. Hot melt granulation: A subdivision of wet granulation in which the binder is melted to facilitate nucleation. This route allows for higher productivity due to improved granulation efficiency and a significant reduction in dryer capacity requirements (which can be a bottleneck for many granulation plants).

[0010] There is a need for a granulation process that overcomes some of the drawbacks known in the art, including using less water, reducing energy demands and improving granulation efficiency. Summary of the Invention [Means for solving the problem]

[0011] Summary of the Invention According to a first aspect of the present invention there is provided a process for the preparation of polyhalite granules comprising the steps of: a) providing an aqueous ammonium nitrate (AN) solution; b) heating the solution to form a hot solution; c) adding the hot solution to the polyhalite; and d) Cooling the mixture during the granulation process.

[0012] The polyhalite granules may contain nitrogen in the form of ammonia and / or nitric acid.

[0013] Ammonium nitrate (AN) is a chemical compound with the formula NH4NO3. AN accounts for over 15% of the world's nitrogen fertilizer demand. AN is a crystalline salt composed of ammonium and nitrate ions. AN is highly soluble in water and hygroscopic as a solid, but does not form hydrates.

[0014] Although AN is less concentrated in terms of nitrogen content than urea, and urea is also cheaper, AN is more suitable because, unlike urease from urea, it contains nitrogen in both the form of ammonia (required by plants) and the form of nitrate. This characteristic ensures less ammonia and NO loss to the atmosphere compared to losses with urease.

[0015] The aqueous AN solution can be of any concentration, but is preferably concentrated to greater than 90% by weight AN, more preferably between about 91.3-98.3% and most preferably approximately 92% by weight AN (w / w).

[0016] The AN solution is heated to improve 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 also increasing the temperature at which the transition phase for AN occurs, improving the product's safety during processing and storage.

[0017] The hot AN solution can be added to the 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).

[0018] The AN solution is preferably heated to a temperature of at least 100°C and preferably between about 126 degrees Celsius (°C) and about 160 degrees Celsius (°C), more preferably between about 145°C and about 150°C.

[0019] The process may include coating the granules with a combination of oil / wax and / or talc to prevent moisture absorption, caking and dusting.

[0020] The process according to the invention may include a step in which the polyhalite granules are sieved into physical sizes above and below the size of the granules sent to the recycle circuit.

[0021] The polyhalite may be combined with a potassium source, such as potassium chloride, potassium nitrate, langbeinite and / or potassium sulfate and / or other potassium-containing minerals / substances.

[0022] The polyhalite granules may further comprise boron, colemanite, colemanite, or any combination thereof, and / or zinc oxide or zinc sulfate and molybdenum (as ammonium molybdate or sodium molybdate dihydrate). In one embodiment, boron, colemanite, colemanite, or any combination thereof, and / or zinc oxide or zinc sulfate and molybdenum (as ammonium molybdate or sodium molybdate dihydrate) may be added to the polyhalite and / or polyhalite-thermal AN mixture.

[0023] Boron may 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).

[0024] Zinc may 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).

[0025] Polyhalite granules prepared according to the present invention may typically have a particle size range of about 1.0 mm to about 6.0 mm, preferably 2.0 mm to 4.0 mm, and even more preferably 2.7 mm to 3.1 mm.

[0026] The average particle size of the polyhalite granules may 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.

[0027] The granulation process can be carried out using a granulator selected from a drum granulator, but different equipment can be used such as, for example, a pan granulator, a granulation tower, an intensive mixer such as an Eirich® intensive mixer, high shear, fluidized bed, hot and cold spheronizer or any other type or combination of equipment capable of producing granules.

[0028] The process according to the invention may further include the use of a dryer. The dryer conditions depend on the AN:polyhalite ratio. For the claimed range (between 50 and 95% by weight AN), the inlet temperature should be about 150-300°C, more preferably in the range of about 150-275°C, even more preferably in the range of about 150-200°C, and should not be higher than about 300°C to avoid decomposition of the ammonium nitrate. The outlet temperature of the gas can be as high as 125°C, but should preferably be between about 90-100°C.

[0029] The pH of the granulator can be controlled and can be greater than about 4.5, and even more preferably greater than about 5.0.

[0030] The process according to the present invention can follow a conventional drum granulation process, whereby the solid polyhalite powder and recycle are fed into a drum granulator. The hot AN solution can be fed into the granulator by a sparger.

[0031] According to a second aspect of the present invention, there is provided a polyhalite granule comprising potassium ammonium nitrate. (Nitrammite or Gwihabaite is the mineralogical name for (NH4,K)NO3.) The granule may contain at least 10% w / w, 20% w / w, 30% w / w, 40% w / w, or 50% w / w of potassium ammonium nitrate. The granule may be produced by a process according to the present invention.

[0032] The granules may further comprise potassium nitrate, calcium ammonium nitrate, ammonium nitrate and / or magnesium nitrate.

[0033] The polyhalite granules may contain nitrogen in the form of ammonia and / or nitric acid.

[0034] According to a third aspect of the present invention, there is provided a process for the preparation of polyhalite granules in which polyhalite is granulated with ammonium nitrate to form potassium nitrate, calcium ammonium nitrate, ammonium nitrate and / or magnesium nitrate. DETAILED DESCRIPTION OF THE INVENTION

[0035] DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is noted to provide an alternative to agglomeration with a binder by adhesion of mineral particles, and instead uses solidification of the particles within a mixture of hot AN solution and mineral polyhalite during a granulation process, such as a drum granulation process.

[0036] The present invention uses hot ammonium nitrate (AN) solution concentrated to 92%-98% AN by weight to bind polyhalite powder and / or granules together. The use of AN in the present invention works by solidifying / crystallizing as the hot material cools during granulation, and the heat of crystallization is used to evaporate water from the AN solution and any added water, and proper gas flow conditions in the spheronizer facilitate granulation.

[0037] Without being bound by theory, Applicants believe that the polyhalite provides a solid bed for crystallization while the AN solution cools. Between 105-108°C, the AN begins to crystallize / solidify, and at the same time, the polyhalite provides Mg, K, S, and Ca, which can react with the AN and act as additives to alter the AN crystallization curve and provide stabilization against thermal decomposition.

[0038] In one embodiment of the present invention, a ratio of 65 wt% AN:35 wt% polyhalite was used.

[0039] Without being bound by theory, applicants believe that the present process may result in the formation of other nitrates, such as potassium ammonium nitrate, potassium nitrate, magnesium nitrate, calcium nitrate, and calcium ammonium nitrate (CAN), and ammonium sulfate in the granules due to chemical reactions that occur during the process.

[0040] Ammonium nitrate and polyhalite granulation can be understood as a combination of wet granulation and melt granulation, where ammonium nitrate is not melted, but the aqueous solution is heated to further increase the solubility of AN in water, forming a hot solution with 92-98% (w / w) AN. As a result, less water is required for granulation than in wet granulation. This characteristic, combined with the heat released by the crystallization of AN, significantly reduces the energy required to dry the product to the required moisture content (less than 0.3%).

[0041] Some advantages of the process according to the present invention include: -Hot ammonium nitrate solution is used as the liquid phase to promote nucleation of powdered polyhalite. -Providing a solid bed in which ammonium nitrate crystallizes during a phase transition that begins to occur when the bed temperature drops to about 105-108°C. -Polyhalite provides other nutrients to the final product (e.g., Mg, K, Ca, and S). -The other nutrients act as additives for ammonium nitrate, providing better stability and increasing the temperature at which the phase transition occurs. -Other nutrients stabilize the phase temperature of the AN crystallization profile (occurring at approximately 32°C), resulting in less degradation of the granules due to thermal cycling during long-term storage.

[0042] drawing FIG. 1 is a schematic mass balance of the process according to the present invention. FIG. 2 is a schematic representation of a process according to the present invention. FIG. 3 is a photograph of uncoated granules of ammonium nitrate and polyhalite (65:35 w / w) according to the present invention. FIG. 4 is a photograph of coated granules of ammonium nitrate and polyhalite (65:35 w / w) according to the present invention. Figure 5 is a graph of dust generation over time. FIG. 6 is a graph of wear rate over time. FIG. 7 is a graph of moisture sorption for different temperatures. [Brief explanation of the drawings]

[0043] 1 and 2 show a conventional granulation process 10, in which a drum granulator 13 is used to produce fertilizer granules 21 containing N, K, S, Mg, and Ca. Polyhalite powder 11 is fed into the drum granulator 13 at a constant rate (kg / h) to achieve the desired potassium concentration in the final product. Other powders, such as potassium chloride, magnesium oxide, langbeinite, ammonium sulfate, and / or colemanite, may also be added at this stage. Ammonium nitrate solution 12 is added to the granulator 13 using a sparger. The ammonium nitrate begins to crystallize on the solid surface due to a decrease in temperature, and particles are generated and grow. Water is added to the granulator 13 to control the liquid phase. The pH is controlled above 4.5, and if the pH begins to drop, ammonia may be added at a rate of approximately 2-3 kg / t.

[0044] The granulation output is sent to dryer 14, where the granules are dried to a moisture content of 0.5%. The polyhalite and ammonium nitrate granules are then classified to the desired particle size (using sieving section 15), and the fines are returned to the granulator. The coarse courses are crushed by crusher 16 to find the fines that constitute the recycle fed to granulator 13. Particles that meet the desired size pass through cooler 17 and then go to polishing / coating drum 20, where (optionally) talc (to prevent caking) 19 and oil (to prevent dusting) 18 are added to coat the particles. The product 21 exiting cooler 17 should be below 45°C or at least about 20°C below room temperature.

[0045] Example 1 A 65 wt.% ammonium nitrate solution was pumped into a drum granulator containing powdered polyhalite and recycle. The powdered polyhalite was fed at a ratio of 35 wt.%, while the recycle ratio was maintained at 5.0. The final product had 0.18% moisture, 21.9% N, 5.0% K (KO), 2.15% MgO, and 7.35% S (in the form of sulfate). The average crushing strength was 8.7 kgf, and the product particle size distribution was 98% between 2 and 5 mm. The product is shown in Figure 3. After cooling, the final product was coated with powder and oil to reduce solidification tendency and dust generation, and is shown in Figure 4. The batch was designated "Batch A" of polyhalite granules containing ammonium nitrate (PGAN).

[0046] The above process was repeated and a second batch of granules designated PGAN "Batch B" was produced.

[0047] PGAN Batch A was prepared under 100% relative humidity compared to PGAN Batch B, which was prepared under dryer and warmer conditions.

[0048] PGAN Batch B had the following properties:

[0049] [Table 1]

[0050] [Table 2]

[0051] [Table 3]

[0052] The size guide number (SGN) is the average (not median) particle size multiplied by 100.

[0053] Uniformity Index (UI) is a formula for particle size uniformity. The uniformity range is 40-60. It is calculated as d95 / d10x100.

[0054] [Table 4]

[0055] The CPG is conventional polyhalite granules ("CPG") containing 99.2% w / w polyhalite and 0.8% w / w cornstarch.

[0056] [Table 5]

[0057] * Bag Hardness - After removing the "dummy" weight, the test bags are inspected without moving them from their original position. The inspector "feels" each bag and records the condition of the bag as light, medium, or hard. * % Clumps - % of clumps +12.5mm after dropping the test bag twice from a height of 1m and then sieving very gently. * Lump Hardness - Graded by crushing in the hands. Light - easily breakable. Medium - breakable when pressed against a hard surface. Hard - cannot be broken without mechanical means.

[0058] [Table 6]

[0059] [Table 7]

[0060] In Table 7: nd = not detected SV = Potash rock salt PHL = Polyhalite HL = Halite AHD=Anhydrite MAG = Magnesite UR=Urea GLB=Lime mirabilite PAN = potassium ammonium nitrate (gwihavite-K) AC = ammonium chloride (chlorammonite) SN = Sodium nitrate (Chilean saltpeter) ANS = ammonium nitrate sulfate AMSH = ammonium magnesium sulfate hydrate (boussingauite)

[0061] Dust generation as a function of time for both Batch A and Batch B is shown in FIG.

[0062] The wear rate as a function of time for both Batch A and Batch B is shown in Figure 6 .

[0063] The moisture absorption at different temperatures for batch B is shown in FIG.

Claims

1. A process for the preparation of polyhalite granules comprising the steps of: a) providing an aqueous ammonium nitrate (AN) solution; b) heating the solution to form a hot solution; c) adding the hot solution to the polyhalite; and d) Cooling the mixture during the granulation process.

2. 10. The process of claim 1, wherein the aqueous AN solution is concentrated to greater than 80 wt% AN.

3. 3. The process of claim 1 or 2, wherein the aqueous AN solution is concentrated to approximately 92 wt. % AN.

4. 10. The process of any preceding claim, wherein the hot solution is added to a bed of polyhalite particles and / or powder.

5. The process of any preceding claim, wherein the hot AN solution is added to the polyhalite in a weight ratio (AN solution:polyhalite) of 50:50 to 95:

05.

6. 10. The process of any preceding claim, wherein the hot AN solution is heated to a temperature between 126 degrees Celsius (°C) and 160 degrees Celsius (°C).

7. 10. The process of any preceding claim, further comprising coating the granules with a combination of oil / wax and / or talc to prevent moisture absorption, caking and / or dusting.

8. 10. The process of any preceding claim, further comprising a step in which the polyhalite granules are sieved into physical sizes above and below the size of the granules sent to the recycle circuit.

9. The process of any previous claim utilizing a granulator selected from a drum granulator, pan granulator, granulation tower, intensive mixer, high shear, hot and cold spheronizer, fluidized bed or any other type or combination of equipment capable of producing granules.

10. 10. The process of any preceding claim, wherein the polyhalite is combined with another potassium source comprising potassium nitrate, langbeinite and / or potassium sulfate and / or other potassium-containing minerals / substances.

11. 10. The process of any preceding claim, wherein boron, colemanite, scutellaria, or any combination thereof, and / or zinc oxide or zinc sulfate and molybdenum (as ammonium molybdate or sodium molybdate dihydrate) are added to the polyhalite and / or polyhalite-hot AN mixture.

12. 10. The process of any preceding claim, wherein the granules have a particle size range of 1.0 mm to 6.0 mm.

13. 10. The process of any preceding claim, further comprising drying the granules using a dryer.

14. 15. The process of claim 14, wherein the dryer conditions are no higher than about 300°C.

15. A process for the preparation of polyhalite granules, wherein polyhalite is granulated with ammonium nitrate to form potassium nitrate, calcium ammonium nitrate, ammonium nitrate and / or magnesium nitrate and ammonium sulfate.

16. Polyhalite granules containing polyhalite and potassium ammonium nitrate.

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

18. Polyhalite granules according to claim 16 or 17, produced by the process according to any one of claims 1 to 15.

19. The polyhalite granules according to any one of claims 16 to 18, further comprising potassium nitrate, calcium ammonium nitrate, ammonium nitrate and / or magnesium nitrate.

20. Polyhalite granules according to any one of claims 16 to 19, containing nitrogen in the form of ammonia and / or nitric acid.

Images