PL249040B1 - Method for producing granulated multi-component fertilizer based on polyhalite and urea and granulated multi-component fertilizer based on polyhalite and urea - Google Patents

Abstract

The subject of the invention is a method for producing a granulated multi-component fertilizer based on polyhalite and urea, which comprises the following steps: a) mechanochemical activation of a mixture of polyhalite and urea, in which the mass ratio of polyhalite to urea is in the range of 0.5:1 to 3:1; b) thermochemical activation - the mixture is heated to a temperature of 100°C to 120°C and mixed for 10 to 240 min, obtaining a process pulp at a temperature of 100°C to 130°C; c) granulation - granules 3-5 mm in size are produced from the melt formed after solidification and cooling of the process pulp. The invention also relates to a granulated multi-component fertilizer based on polyhalite and urea, which is characterized in that it contains N in an amount of 13.0% - 28.0%; K2O in the amount of 5.5% — 10.2%; CaO in the amount of 7.3% — 13.3%; MgO in the amount of 2.4% — 4.4%; S in the amount of 8% - 14.7%.

Description

Description of the invention

The invention is a method for producing a granulated multi-component nitrogen-potassium fertilizer containing secondary plant nutrients, as well as a granulated multi-component nitrogen-potassium fertilizer containing secondary nutrients, wherein the potassium source is polyhalite and the nitrogen source is urea, for use in the agricultural industry. The method is characterized by the use of uncalcined polyhalite and urea in crystalline or granulated form, and by eliminating the need for granulating agents, including water. The conditions under which it is carried out favor the formation of calcium and magnesium sulfate adducts with urea.

Polyhalite is a mineral containing potassium in the sulfate form. A disadvantage of this mineral, when used as a fertilizer, is its slower action compared to other potassium fertilizers. Information on methods for producing granulated polyhalite and fertilizer compositions containing it is available in the available literature. This allows for the polyhalite to be given a physical form that facilitates its turnover and application, as well as the creation of fertilizer compositions with additives that accelerate the action of the nutrients contained in polyhalite. Such additives include, among others, nitrogen compounds, which can accelerate the yield-forming effect of polyhalite.

Polish patent description no. PL241178 B1 presents a multi-component fertilizer composition in the form of granules and a method for its production. The fertilizer composition presented consists of polyhalite and carbonate flour, which may be chalk, limestone, dolomite, magnesite, or marl. Potassium chloride added in the form of sylvite or sylvinite can be an additional source of potassium. The main advantage of the composition is the accelerated disintegration of granules in soil conditions due to the addition of calcium and/or magnesium carbonates. The described method is based on the introduction of limestone or magnesium carbonate flour to the system as a factor facilitating granule disintegration, while water is used as the binding liquid. However, the granules produced in this way, especially after seasoning and the associated water loss, will be characterized by very poor mechanical resistance, which will contribute to their excessive disintegration during storage and transport, thus reducing the usefulness of the resulting compositions.

A method for producing fertilizer granules from polyhalite is also known from patent description PL241460 B1. It refers to a method for producing a fertilizer composition from a mineral or mineral and organic material by using a nitrogen fertilizer containing ammonium or nitrate and amide nitrogen as a solubilizing agent. It involves grinding the granulated nitrogen fertilizers to obtain a micronized form, then transferring the material to a disk granulator and adding the micronized form of polyhalite. The described method allows for the use of a binder liquid in the granulation process. According to the disclosed description, the granulation method allows for obtaining agglomerates with a very diverse diameter (1-10 mm), with a 2-6 mm fraction being desirable. The described method involves two grinding operations: one for the nitrogen fertilizer and the other for the polyhalite, which increases the degree of complexity. Additionally, as a result of mixing polyhalite with a source of amide nitrogen and a mineral acid, gaseous by-products of the reactions may be released during granulation, which will reduce the mechanical strength of the obtained granulates.

A fertilizer containing polyhalite and urea, as well as ammonium sulfate and mineral flour, is the subject of patent application No. WO2021059261 A1. The production method disclosed in this description involves treating a mixture of polyhalite, urea, and mineral flour with sulfuric acid, followed by ammonization of the resulting mixture and its granulation in a drum granulator. This solution, due to the possibility of a reaction between sulfuric acid and urea, may be disadvantageous. The reaction between sulfuric acid and urea can release a large amount of heat, which can pose a safety risk. Additionally, the aforementioned reaction can result in the formation of amido compounds harmful to plants. A method for producing a fertilizer containing polyhalite and urea is also known from patent application No. WO2017081470 A1. It discloses a method for producing a granular layered fertilizer where the core is urea, which is surrounded by a coating composed of polyhalite and starch. The disadvantage of this method is the inability to produce a homogeneous mixture of polyhalite and urea, which significantly limits the possibility of activating the potassium raw material.

Unexpectedly, it turned out that mixing polyhalite with urea at 100-120°C produces pulp, producing stable adducts CaSO4-4CO(NH2)2 and MgSO4-CO(NH2)2, as determined by XRD analyses. The possibility of pulp formation below the melting point of urea indicates that urea can disrupt the structure of polyhalite, causing its dehydration, thereby releasing water present in its structure, which gives the mixture a fluid consistency. The resulting pulp is suitable for granulation at temperatures at which urea decomposition does not occur.

The present invention is a production method (including a fertilizer composition containing polyhalite and urea) that, through the formation of stable adducts, is characterized by modified nutrient availability, i.e., increased availability and rapid availability of nutrients contained in polyhalite to plants, and a reduced release rate of nitrogen contained in the fertilizer in the form of urea. The fertilizer production process involves the formation of pulp, which occurs through mechanochemical and thermochemical activation of the polyhalite and urea mixture, followed by mechanical granulation: drum or disc. The granulate thus produced is subjected to drying and classification, which involves the screening of undersized fractions (undersized or oversized particles), which are then subjected to regranulation (in the case of oversized particles, after secondary fragmentation). Additionally, during the mechanochemical and thermochemical activation of the polyhalite and urea mixture, a small amount of water (5 to 10% by weight) may be added, which facilitates pulp production. Optionally, drying of the resulting granulate is permitted, particularly when it contains more than 6% by weight of water.

The essence of the invention is a method for producing a granulated multi-component fertilizer based on polyhalite and urea, which includes the following steps:

a) mechanochemical activation, during which a mixture of polyhalite and urea is ground, in which the mass ratio of polyhalite to urea is in the range of 0.5:1-3:1;

b) thermochemical activation, during which the mixture is heated to a temperature of 100 to 120°C and mixed for 10 to 240 minutes, obtaining a process pulp with a temperature of 100 to 130°C;

c) granulation, during which granulates of 3-5 mm size are produced from the melt formed after solidification and cooling of the process pulp.

It is advantageous when polyhalite contains nutrients selected from the group: potassium - 14.04% by mass K2O, calcium - 18.60% by mass CaO, magnesium - 6.38% by mass MgO.

Preferably, the nitrogen content in urea is 46.2% by mass.

Preferably, the polyhalite is ground to a particle size of less than 0.10 mm.

Preferably, in step a) the process of mechanochemical activation of the mixture of polyhalite and urea is carried out in a ball mill until the grain size of the activated mixture is below 0.1-0.2 mm.

Preferably, 20 g of water is added in step a).

Preferably, in step b) the mixing is carried out for 25-35 minutes.

Preferably, in step b) a process pulp is obtained at a temperature of 107 to 120°C.

Granulated multi-component fertilizer based on polyhalite and urea, produced by the method described above, is characterized in that it contains N in the amount of 13.0-28.0%; K2O in the amount of 5.5-10.2%; CaO in the amount of 7.3-13.3%; MgO in the amount of 2.4-4.4%; S in the amount of 8-14.7%.

The research demonstrated that the proposed process produced agglomerates with high mechanical strength and physical stability, even after long-term storage. Additionally, the resulting fertilizer was characterized by increased hygroscopicity compared to other granular fertilizers, which resulted in increased water sorption in soil conditions and, consequently, increased nutrient absorption.

The invention is presented in more detail in the examples. The first three examples involve the same product composition but different pulp preparation times. The subsequent examples involve products with different polyhalite and urea contents and the same pulp preparation time. The same polyhalite and urea were used to conduct the fertilizer production tests, the results of which are presented in the examples. The nutrient content of the polyhalite used in the tests was equal to:

• potassium: 14.04% K2O, • calcium: 18.60% CaO, • magnesium: 6.38% MgO,

The nitrogen content in urea was 46.2% by mass.

For the tests presented in Examples 1-3, 111.5 g of polyhalite and 88.5 g of urea were used in each case. The contents of nutrients such as potassium, calcium, and magnesium in the obtained products are expressed as oxides. Nitrogen and sulfur contents are expressed as elemental values.

Example 1

111.5 g of polyhalite ground to less than 0.10 mm and 88.5 g of granulated urea were introduced into a stirred laboratory reactor equipped with a heating jacket and allowing for smooth temperature control and measurement. After the raw materials were introduced, the reactor was slowly heated to 120°C. After 10 minutes of heating and stirring, a pulp was obtained at a temperature of 115-120°C (of a consistency that allowed the vast majority of the pulp to be poured from the reactor without assistance). The reactor was then emptied, and the melt formed after solidification and cooling of the pulp was used to produce granulates measuring 3-5 mm and tested. The average compressive strength of the agglomerates immediately after production was found to be 203 N, while after 60 days of storage, it was 228 N. After maturing for three days in an atmosphere with 50% relative humidity, the product absorbed approximately 0.78% water. The obtained product contained: 20.4% by mass of N; 7.7% by mass of K2O; 10.4% by mass of CaO; 3.5% by mass of MgO and 10.3% by mass of S. Urea bound in the form of adducts constituted 45% of the total urea present in the fertilizer.

Example 2

111.5 g of polyhalite ground to less than 0.10 mm and 88.5 g of granular urea were introduced into a laboratory reactor equipped with a stirrer and a heating jacket with continuous temperature control and measurement. After the raw materials were introduced, the system was slowly heated to 100°C. After 10 minutes of heating and mixing, a pulp was obtained at a temperature of 115-120°C (of a consistency that allowed the vast majority of the pulp to be poured from the reactor without assistance). The reactor contents were stirred for 10 minutes while maintaining the temperature at approximately 120°C. After this time, the reactor was emptied, and the melt formed after solidification and cooling of the pulp was processed into granulates measuring 3-5 mm in size, which were then tested. The average compressive strength of the particles immediately after production was found to be 192 N, while after 60 days of storage it was equal to 238 N. The product stored for 3 days in an atmosphere with 50% relative humidity absorbed approximately 0.67% water. The obtained product contained: 20.5% by weight N; 7.8% by weight K2O; 10.5% by weight CaO; 3.4% by weight MgO and 10.5% by weight S. In the resulting agglomerates, 43% of urea was bound in the adduct.

Example 3

111.5 g of polyhalite ground to less than 0.10 mm, 88.5 g of granular urea, and 20 g of water were added to a laboratory reactor, which allowed for stirring and free heating of the mixture to 120°C. After adding the raw materials, the reactor was slowly heated to 110°C. After 10 minutes of heating and stirring, a pulp was obtained at a temperature of 115-120°C (of a consistency that allowed the vast majority of the pulp to be poured from the reactor without assistance). The reactor contents were stirred for 240 minutes, maintaining a constant temperature. After this time, the reactor was emptied, and the melt formed as a result of cooling and solidification of the pulp was used to produce granules measuring 3-5 mm. The resulting fertilizer was then tested. It was found that the average compressive strength of the agglomerates immediately after their production was 232 N, while after 60 days of storage it was 196 N. The product seasoned for 3 days in an atmosphere with 50% relative humidity absorbed approximately 2.39% water. The product contained: 20.7% by weight N; 7.7% by weight K2O; 10.4% by weight CaO; 3.6% by weight MgO and 10.1% by weight S. The share of urea bound in the adduct was 49%.

Example 4

111.5 g of polyhalite ground to less than 0.10 mm and 44.25 g of granulated urea were added to a laboratory reactor equipped with a stirrer and a temperature-controlled heating jacket. After the raw materials were added, the reactor was slowly heated. After 10 minutes of heating and stirring, a pulp was obtained at a temperature of approximately 120°C (of a consistency that allowed the vast majority of the pulp to be poured from the reactor without assistance). The reactor contents were stirred for 30 minutes while maintaining a constant temperature of 120°C. The resulting pulp was mechanically granulated, yielding mostly granulates with a diameter of 3-5 mm, which were then tested. The average compressive strength immediately after agglomeration was found to be 109 N, and after 60 days of storage, it was 120 N. The product, seasoned for 3 days in an atmosphere with 50% relative humidity, absorbed approximately 2.27% water. The obtained product contained: 13.0 wt.% N; 10.2 wt.% K2O; 13.3 wt.% CaO; 4.4 wt.% MgO and 13.7 wt.% S. The content of urea bound in the adduct in this product was 65%.

Example 5

111.5 g of polyhalite ground to less than 0.10 mm, 66.4 g of granular urea, and 10 g of water were added to a laboratory reactor equipped with a stirrer and a heating jacket, allowing the reactor contents to be heated to 120°C. After the raw materials were added, the reactor was slowly heated. After 10 minutes of heating and mixing, a pulp was obtained at a temperature of 110-115°C (of a consistency that allowed the vast majority of the pulp to be poured from the reactor without assistance). The reactor contents were stirred for 30 minutes, maintaining the temperature at 110-115°C. The resulting pulp was mechanically granulated, yielding granules with a predominance of granules with a diameter in the range of 3-5 mm, which were then subjected to testing. The average compressive strength of the granules, immediately after their production, was found to be 177 N, and after 60 days of storage - 266 N. The product seasoned for 3 days in an atmosphere with 50% relative humidity absorbed approximately 1.2% water. The product produced during the test contained: 17.0% by weight N; 8.9% by weight K2O; 4.0% by weight MgO; 11.8% by weight CaO; and 11.9% by weight S. The content of urea bound in the adduct in the produced granules was 46%.

Example 6

77.3 g of polyhalite ground to less than 0.10 mm and 122.7 g of granulated urea were weighed into a laboratory reactor equipped with a stirrer and a heating jacket. After the raw materials were added, the reactor was slowly heated. After 10 minutes of heating and stirring, a pulp was obtained at a temperature of approximately 120°C (of a consistency that allowed the vast majority of the pulp to be poured from the reactor without assistance). The reactor contents were stirred for 30 minutes while maintaining the mixture temperature at 120°C. The reactor was then emptied, and the resulting pulp was subjected to mechanical granulation. The resulting granules, 3-5 mm in diameter, were tested. The average compressive strength of the agglomerates immediately after production was found to be 154 N, and after 60 days of storage, it was 192 N. After maturing for three days in an atmosphere with 50% relative humidity, the product absorbed approximately 0.33% water. The product produced during the test contained: 28.0 wt.% N; 5.5 wt.% K2O; 7.3 wt.% CaO, 2.4 wt.% MgO and 8.0 wt.% S. The urea content in the product, which was bound in the adduct, was equal to 11%.

Example 7

A mixture containing 143.7 g of polyhalite and 56.3 g of urea, previously mechanochemically activated, was introduced into a laboratory reactor equipped with a stirrer and a heating jacket. After the raw materials were added, the system was slowly heated to 120°C and stirred. After 10 minutes, a pulp was obtained at a temperature of approximately 120°C (of a consistency that allowed the vast majority of the pulp to be poured from the reactor without assistance). The reactor contents were stirred for 30 minutes while maintaining the mixture temperature at 120°C. The reactor was then emptied, and the resulting pulp was mechanically granulated, yielding mostly granules with a diameter in the range of 3-5 mm, which were then subjected to testing. It was found that the average crushing strength of the agglomerates immediately after their production was 115 N, while after 60 days of storage it was equal to 117 N. The product seasoned for 3 days in an atmosphere with 50% relative humidity absorbed approximately 1.89% water. The produced product contained: 13% N by mass; 10.2% K2O by mass; 13.3% CaO by mass; 4.4% MgO by mass; 14.7% S by mass. The urea content in the product, which was bound in the adduct, was equal to 68%.

Claims (9)

1. A method for producing a granulated multi-component fertilizer based on polyhalite and urea, characterized in that it comprises the following steps: a) mechanochemical activation, during which a mixture of polyhalite and urea is ground, in which the mass ratio of polyhalite to urea is in the range of 0.5:1-3:1; b) thermochemical activation, during which the mixture is heated to a temperature of 100 to 120°C and mixed for 10 to 240 min, obtaining a process pulp with a temperature of 100 to 120°C; c) granulation, during which granulates of 3-5 mm size are produced from the melt formed after solidification and cooling of the process pulp. 2. The method according to claim 1, characterized in that the polyhalite contains nutrients selected from the group: potassium - 14.04% by mass K2O, calcium - 18.60% by mass CaO, magnesium - 6.38% by mass MgO. 3. The method according to claim 1, characterized in that the nitrogen content in urea is 46.2% by mass. 4. The method according to claim 1, characterized in that the polyhalite is ground to a particle size of less than 0.10 mm. 5. The method according to claim 1, characterized in that in step a) the process of mechanochemical activation of the mixture of polyhalite and urea is carried out in a ball mill until the grain size of the activated mixture is below 0.1-0.2 mm. 6. The method according to claim 1, characterized in that in step a) water is added in an amount of 20 g. 7. The method according to claim 1, characterized in that in step b) the mixing is carried out for 25-35 minutes. 8. The method according to claim 1, characterized in that in step b) a process pulp is obtained at a temperature of 107 to 120°C. 9. Granulated multi-component fertilizer based on polyhalite and urea, produced by the method defined in claim 1, characterized in that it contains N in the amount of 13.0-28.0%; K2O in the amount of 5.5-10.2%; CaO in the amount of 7.3-13.3%; MgO in the amount of 2.4-4.4%; S in the amount of 8-14.7%.