Mixed fertilizer granules

Abstract

The present invention relates to a fertilizer in granular form comprising, in the same granule, a mixture of: (A) 15% to 85% by weight of potassium sulfate; and (B) 85% to 15% by weight of at least one salt different from (A) and providing potassium and / or magnesium and / or calcium and / or sulfate; wherein the fertilizer in granular form has a potassium level (expressed as K2O) of at least 18% by weight, preferably at least 20% by weight; a chloride level of at most 10% by weight, preferably at most 5% by weight, more preferably at most 3% by weight; and a magnesium level (expressed as MgO) of at most 10% by weight, preferably at most 9.5% by weight. The material of the invention is free-flowing and combines a good nutritional balance with good hardness and abrasion resistance.

Description

Technical Field

[0001] The present invention relates to the field of fertilizers, and more particularly to the field of mixed fertilizers in the form of free-flowing granules having sufficient hardness and good abrasion resistance. Background Art

[0002] As is well known, fertilizers are used in agricultural and horticultural applications. A number of nutrients are thereby supplied to the soil or growing medium of the plant. Nutrients such as nitrogen, phosphorus, potassium, calcium, magnesium and sulfur are supplied in relatively large quantities, while many other elements are supplied in smaller quantities, as micronutrients.

[0003] Solid fertilizers come in the form of granules, pellets, powders and crystals. SOP (sulfate of potash) is primarily sold as a granular fertilizer and is usually mixed with other fertilizers such as N or P fertilizers (via bulk blending).

[0004] Farmers want K fertilizers to be easily spread on the fields along with N or P fertilizers. The fertilizer industry requires a product that is free-flowing, easy to package, store and transport and has low segregation. When the granules have good hardness and abrasion resistance, then the granules will be less prone to breaking and will be easier to apply.

[0005] The industry is constantly searching for new K fertilizers with a good nutrient balance, a high enough potassium content and a low enough chloride content.

[0006] Due to differences in properties and behavior, it is not always simple to combine different fertilizers or nutrient elements in the same fertilizer granule.

[0007] Recently, there has been interest in using evaporite minerals such as polyhalite, uraninite, weathered lignite, anhydrous kainite, etc. Polyhalite is an evaporite mineral, a hydrated salt of potassium, magnesium, and calcium with the formula: K 2 Ca 2 Mg(SO 4 ) 4 .2H 2 O. Uranium ore (or kainite) is another brine evaporite, composed of a mineral with the chemical formula K 2 Mg(SO4) 2 .6(H 2 O) is a mixed potassium and magnesium sulfate composition. Leonidite and langbeinite are other examples of mixed potassium and magnesium salts.

[0008] The problem with polyhalite is that it is difficult to pelletize. It is a coarse material and under normal conditions, deformation of polyhalite pellets is difficult. This is also true for uraninite and other mixed or double sulfates. Another problem with polyhalite, etc. is the low (lower) K 2 O levels and low K 2 O / MgO ratio.

[0009] WO2019 / 086062 describes fertilizer granules consisting essentially of potassium, magnesium, calcium and sulfate and containing polyhalite mixed with potash (KCl). The granules described therein contain up to 13% by weight of potassium.

[0010] WO2018 / 146884 describes a polyhalite granulation method. However, the granules obtained have a K that is too low for many applications. 2 O level and too low hardness.

[0011] WO2018 / 229757 describes a compacted polyhalite and potash (KCl) mixture. Due to the high amount of KCl, the chloride level in this case is too high for general use and especially for chloride-sensitive crops. In this document, it is mentioned that unique compaction conditions are required for polyhalite granulation. Summary of the invention

[0012] The present invention provides a fertilizer in granular form, which comprises a mixture of the following substances in the same granule: based on the total amount of salt,

[0013] (A) 15 to 85 wt% potassium sulfate (K 2 SO 4 , also known as sulfate of potash or SOP); and

[0014] (B) 85% to 15% by weight of at least one salt different from (A) providing potassium and / or magnesium and / or calcium and / or sulfate;

[0015] The granular fertilizer has

[0016] - at least 18% by weight, preferably at least 20% by weight of K 2 O's potassium level;

[0017] - a chloride level of at most 10 wt%, preferably at most 5 wt%, typically at most 3 wt%; and

[0018] - A magnesium level expressed as MgO of at most 10 wt.-%, preferably at most 9.5 wt.-%.

[0019] The skilled person will understand that, as used herein, 85% to 15% by weight of at least one salt different from A refers to the total content of all such salts different from A.

[0020] Preferably, the magnesium level in any of the above (expressed as MgO) is at most 9.9 wt%, 9.8 wt%, 9.7 wt%, 9.6 wt%, more preferably at most 9.5 wt%, 9.4 wt%, 9.3 wt%, 9.2 wt%, 9.1 wt% or 9 wt%. When present, the magnesium level is at least 0.001 wt%, preferably at least 0.01 wt%, more preferably at least 0.1 wt%, at least 0.5 wt%. In a preferred embodiment of the invention, the magnesium level is at most 8.5 wt%, 8.4 wt%, 8.3 wt%, 8.2 wt%; 8.1 wt%, preferably at most 8 wt%, 7.9 wt%, 7.8 wt%, 7.7 wt%, 7.6 wt%, 7.5 wt%, 7.4 wt%, 7.3 wt%, 7.2 wt%, 7.1 wt%, 7 wt%.

[0021] The calcium level in any of the above (described as CaO) is at most 10 wt%, 9.9 wt%, 9.8 wt%, 9.7 wt%, 9.6 wt%, more preferably at most 9.5 wt%, 9.4 wt%, 9.3 wt%, 9.2 wt%, 9.1 wt% or 9 wt%. When present, the calcium level is at least 0.001 wt%, preferably at least 0.01 wt%, more preferably at least 0.1 wt%, at least 0.5 wt%. In a specific embodiment, the calcium level is at least 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%. In the same or another embodiment, the calcium level is at most 5 wt%, 4.5 wt%, 4 wt%.

[0022] Preferably, the potassium level (expressed as K 2 O) is at least 18 wt.%, 19 wt.%, 20 wt.%, 21 wt.%, 22 wt.%, 23 wt.%, 24 wt.%, more preferably at least 25 wt.%, 26 wt.%, 27 wt.%, 28 wt.%, 29 wt.%, most preferably at least 30 wt.%.

[0023] Preferably, the sulfate level (expressed as SO 3 ) is 40 to 55% by weight, preferably 40 to 50% by weight.

[0024] Preferably, K 2 The O / MgO ratio (expressed as a weight % ratio) is at least 3, 3.1, 3.2, 3.3, 3.4, preferably at least 3.5, 3.6, 3.7, 3.8, 3.9, more preferably at least 4, 4.5, 5, 5.5 or even at least 6 or more.

[0025] The term 'wt%' herein stands for 'weight percent' or 'weight %'. The preferred composition and preferred features of the granular fertilizer of the present invention of any one of the above are described in detail below.

[0026] Preferably, potassium sulfate (A) is present in the fertilizer in granular form in an amount of at least 15%, 16%, 17%, 18% or 19% by weight, preferably at least 20%, 21%, 22%, 23%, 24% or 25% by weight, based on the total amount of salts. Preferably, salt (B) is present in the fertilizer in granular form in an amount of at least 15%, 16%, 17%, 18% or 19% by weight, preferably at least 20%, 21%, 22%, 23%, 24% or 25% by weight, based on the total amount of salts.

[0027] Preferably, based on the total amount of salt, there are 20% to 80% by weight of salt (A) and 80% to 20% by weight of salt (B). More preferably, there are 30% to 70% by weight of salt (A) and 70% to 30% by weight of salt (B). Most preferably, there are 40% to 60% by weight of salt (A) and 60% to 40% by weight of salt (B). In a preferred embodiment of the present invention, based on the total amount of salt, the summation of A+B is at least 80%, 85%, 90%, 95%, 96%, 97%, 98% or 99% by weight. Obviously, a summation exceeding 100% by weight is impossible.

[0028] Preferably, potassium sulfate (A) is present in an amount of at least 15%, 16%, 17%, 18% or 19%, preferably at least 20%, 21%, 22%, 23%, 24% or 25%, based on the total weight of the granular fertilizer. Preferably, salt (B) is present in an amount of at least 15%, 16%, 17%, 18% or 19%, preferably at least 20%, 21%, 22%, 23%, 24% or 25%, based on the total weight of the fertilizer.

[0029] The above amounts (expressed in weight percent) include typical impurities, by-products, residual reactants or possible water of crystallization, which usually remain and are not removed.

[0030] Preferably, the potassium sulfate (A) and the at least one salt (B) described herein are distributed more or less uniformly on the fertilizer particles, possibly without including a coating.

[0031] In some embodiments of the invention, it may be preferred to use potassium sulfate (A) produced via the Mannheim process in the muffle furnace.

[0032] Salt (B) is a salt that provides additional potassium and / or magnesium and / or calcium and / or additional sulfate. Salt (B) is preferably a sulfate, and more preferably a double salt or a mixed salt. A "mixed" salt means that at least two different cations are provided by the salt, for example (1) potassium and (2) magnesium. Typically, the K of salt (B) is 2 O levels are below 45, 44, 43, 42, 41, 40, 39, 38, 37, more typically below 36, 35, 34, 33, 32, 31, and even more typically below 30.

[0033] In the context of the present invention, potassium magnesium salts and / or potassium magnesium calcium salts are preferred. Very suitable are polyhalite and / or anhydrous kainite and / or leonite and / or uraninite. and / or kainite. Preferred are polyhalite and / or anhydrous kainite and / or weathered lignite and / or uraninite. Most preferred are polyhalite and / or uraninite. It is usually preferred to use the above substances (or their mixtures) in calcined form. For composition, see Table I.

[0034] Preferably, salt (B) is selected from one or more of the following: calcined polyhalite, calcined anhydrous langbeinite, calcined weathered lignite, calcined pillarite, and mixtures thereof (any of these). Particularly preferred is calcined polyhalite and / or calcined pillarite.

[0035] In a preferred embodiment of the present invention, salt (B) consists of polyhalite and / or uraninite, more particularly of calcined polyhalite and / or calcined uraninite. In a specific embodiment of the present invention, salt (B) is polyhalite, a mixture of calcined and uncalcined polyhalite, preferably calcined polyhalite. In another specific embodiment of the present invention, salt (B) is uraninite, a mixture of calcined and uncalcined uraninite, preferably calcined uraninite.

[0036] In addition to the salts (A) and (B), the particles of the invention may also contain a binder, such as a grinding binder or a binder containing a material that increases cohesion and / or hardness. Such binders may be organic and / or inorganic in nature. Such binders may contain one or more of the following ingredients: water, chalk, sodium silicate, potassium silicate, fly ash, geopolymers, starch, cellulose gum, sucrose, lignin sulfate, molasses, magnesium oxide, calcium oxide, lime, slaked lime [Ca(OH) 2 ], asphalt, Portland cement, alginic acid, clays such as bentonite, acids (nitric, hydrochloric, phosphoric, sulfuric), oils, waxes, etc. In particular, it has been found that the use of lime and / or slaked lime, rather than in combination with hydroxides such as chalk, improves particle hardness.

[0037] Besides the salts (A) and (B) and optionally the binder, the particles according to the invention may also comprise further additives and coatings.

[0038] Examples of additives that may be added include dyes, pH aids, (elemental) sulfur, additional macronutrients or micronutrients containing boron, zinc, manganese, nickel, molybdenum, copper, iron, chloride, sodium or combinations thereof, etc. Preferred are those containing boron, zinc, manganese, nickel, molybdenum, copper, iron or combinations thereof (any of these).

[0039] The particles of the present invention may also contain one or more coatings. The coating may be a dust-proof coating and / or an anti-caking coating and / or a slow-release or controlled-release coating and / or a coating containing additional nutrients. Also possible are biodegradable coatings and / or oily or waxy coatings that reduce dust.

[0040] Preferably, the particles of the present invention have been polished or post-treated and glazed, oiled, glazed, etc. to increase hardness and / or reduce dust content. Any oil (e.g., mineral oil) or any wax (e.g., slack wax, paraffin) standard in the art can be used to improve rheology and / or reduce dust content.

[0041] Advantageously, the granules of the invention (or the fertilizer in granular form of the invention) have on average a hardness of at least 2 kg, 2.1 kg, 2.2 kg, 2.3 kg, 2.4 kg, 2.5 kg, 2.6 kg, 2.7 kg. Preferably, the hardness is at least 2.8 kg, 2.9 kg or at least 3 kg. The granules of the invention (or the fertilizer in granular form of the invention) have on average a wear of at most 15 wt.-%, 14 wt.-%, 13 wt.-%, 12 wt.-%, 11 wt.-%, 10 wt.-%, 9 wt.-%, 8 wt.-%, 7 wt.-%, preferably at most 6.5 wt.-%, 6 wt.-%, 5.5 wt.-%, 5 wt.-%, 4.5 wt.-%, 4 wt.-%, 3.5 wt.-%. Most preferably, the wear is at most 3 wt.-%.

[0042] The granules of the invention (or the fertilizer in granular form of the invention) typically have a particle size of 1 mm to 6 mm, more preferably 2 mm to 4 mm. Typically 40% to 70% of the granules obtained with the process of the invention (described further) have a size of 2 mm to 4 mm. In one embodiment of the invention, 40% to 50% of the granules obtained have a size of 2 mm to 4 mm. In a preferred embodiment of the invention, 50% to 95%, even more preferably 60% to 95%, typically 60% to 90% of the granules obtained have a size of 2 mm to 4 mm.

[0043] The process of the invention (described further on) allows the production of sufficiently round and free-flowing granules.

[0044] The mixed fertilizer in granular form of the present invention can be prepared in various ways. Typically, the granules of the present invention are produced by compaction or by a granulation process based on size increase, such as wet roll granulation.

[0045] Granulation is a size enlargement operation by which fine powders or finer materials are aggregated into larger particles to produce a specific size and shape, improve flow and appearance, and reduce dust content. Size enlargement here is preferably by tumbling growth. Both dry granulation and wet granulation exist, but in this context, wet granulation is preferred, and more particularly wet drum granulation.

[0046] Some preferred methods of preparing the particles of the present invention are described below:

[0047] In a first embodiment of the invention, the fertilizer in granular form according to the invention is produced by a compaction method (I) comprising the following steps:

[0048] (i) providing a mixture comprising (a) potassium sulfate (A) and (b) at least one salt (B) different from (A) and providing potassium and / or magnesium and / or calcium and / or sulfate;

[0049] (ii) optionally: adding a binder, preferably a binder comprising water, and mixing, typically until a homogeneous mixture is obtained;

[0050] (iii) compacting the mixture in a compactor to obtain granules;

[0051] (iv) sieving the granules thus obtained to retain granules having a particle size between 1 mm and 6 mm, preferably between 2 mm and 4 mm.

[0052] In a second embodiment of the invention, the fertilizer in granular form according to the invention is produced by a granulation process (II), more particularly a wet tumbling granulation process (II), comprising the following steps:

[0053] (i) providing a mixture comprising (a) potassium sulfate (A) and (b) at least one salt (B) different from (A) and providing potassium and / or magnesium and / or calcium and / or sulfate;

[0054] (ii) adding water (in the required amount) and optionally further binders;

[0055] (iii) mixing, typically until a homogeneous mixture is obtained;

[0056] (iv) forming granules of a desired size in a granulator, preferably a wet drum granulator;

[0057] (v) drying the particles;

[0058] (vi) optionally: sieving the particles thus obtained to retain particles having a particle size between 1 mm and 6 mm, preferably between 2 mm and 4 mm.

[0059] Examples of granulators that can be used in method (II) include, but are not limited to, wet drum granulators, such as disc, drum, pan granulators, drum granulators, gear and drum granulators, etc. Another word for "granulator" is "granulator". Although spray and melt granulation can also be used in theory, they are less preferred in the context of the present invention. We have obtained the best results using wet drum granulators (including disc, drum, and pan granulators).

[0060] Below, preferred modes of operation are provided. Unless otherwise stated, the content mentioned below generally applies to any method of the present invention [such as any method (I) or any method (II) described herein].

[0061] The information of the typical amount of the granular form of salt (A) and salt (B) in the mixed fertilizer has been given above, which is relative to the total amount of salt. Salt (A) and (B) are usually used in such an amount, i.e., relative to the total amount of salt, with 15% to 85% by weight of salt (A) and 85% to 15% by weight of salt (B), 20% to 80% by weight of salt (A) and 80% to 20% by weight of salt (B). More preferably, there are 30% to 70% by weight of salt (A) and 70% to 30% by weight of salt (B). Most preferably, there are 40% to 60% by weight of salt (A) and 60% to 40% by weight of salt (B). Obviously, based on the total amount of salt, the summation of A+B cannot be higher than 100% by weight. In a preferred embodiment of the present invention, the sum of A+B is at least 80%, 85%, 90%, 95%, 96%, 97%, 98% or 99% by weight, based on the total amount of salt.

[0062] Potassium sulfate (A) can have the following sources. It can be:

[0063] - mining and processing to remove unwanted salts, or

[0064] - It is prepared by reacting potassium chloride with sulfuric acid in a potassium sulfate furnace, for example according to the Mannheim process.

[0065] In some embodiments of the present invention, it may be beneficial to use potassium sulfate (A) produced via the Mannheim process in a potassium sulfate furnace. Alternatively, potassium sulfate (A) derived from evaporite minerals may be used. For example, potassium chloride may react with various sulfates to form double salts, which may then be decomposed to obtain potassium sulfate (A). The sulfate reacted with potassium chloride may be sodium sulfate (in the form of Glauber's salt and / or sulfate brine) and / or magnesium sulfate (in the form of kieserite and / or epsom salt).

[0066] In a particular embodiment of the invention, potassium sulfate (A) is at a temperature between 100° C. and 400° C. when mixed with salt (B); more particularly at a temperature between 150° C. and 400° C. Particularly preferred is potassium sulfate (A) just leaving the cooling drum after the muffle furnace when the temperature is close to 200° C. or close to 300° C.

[0067] Preferred salts (B) have been listed above, and as mentioned above, salts (B) are preferably used in their calcined form. When not purchased as such, the process of the invention (any of the above processes) preferably comprises a calcination step (of salt (B)) before mixing salt (B) with salt (A). It is ultimately possible to use a mixture of partially calcined and partially uncalcined salt (B).

[0068] Uranium ore and polyhalite are usually obtained in the form of coarse powder, and potassium sulfate is usually present in the form of particles or powder. However, in the context of the present invention, it is preferred to start from a material having a size of no more than 1000 μm, 900 μm, 800 μm, 700 μm, 600 μm, preferably no more than 500 μm, 400 μm, more preferably no more than 300 μm. This can be achieved by crushing and / or sieving salt (A) and / or salt (B) when necessary. In a preferred embodiment, at least 80% by weight, 85% by weight, 90% by weight, 91% by weight, 92% by weight, 93% by weight, 94% by weight, 95% by weight, 96% by weight, 97% by weight, 98% by weight, or even 99% by weight of the total amount of salt (A) and (B) provided in step (i) have a particle size of no more than 500 μm, preferably no more than 300 μm.

[0069] Crusher that may be used include semi-wet material crushers, chain crushers, hammer crushers, etc. Screening generally involves passing the material through subsequent screens, for example starting with 5 mm and ending with 300 μm.

[0070] In one embodiment of the invention, the crushing and / or screening step precedes step (i). Typically, step (i) is followed by a crushing and / or screening step. Preferably, the crushing and / or screening step precedes the step of adding water and optional other binder materials. Examples of suitable and preferred binding materials can be found above.

[0071] Salt (A) and (B) and possible other ingredients such as binding agent (above examples) are directly mixed. Any mixer producing a more or less uniform mixture can be used. The mixer used in the inventive method (above any method) can be a horizontal or vertical mixer, a paddle mixer or a plough mixer, a turbine mixer, a pin mixer, etc. In the granulation method (II), mixing can be carried out in a granulator, such as a disc or disk granulator. However, it is preferred to have a (separate) mixing step before the granulator.

[0072] The amount of water added depends on the production process. A person skilled in the art knows the amount of water required for a given production process. For example, when compaction (I) is used, then 0.5 to 3 wt % of water is usually added. Most typically, 1 to 2 wt % of water is then used. In wet granulation method (II); more specifically, in wet tumbling granulation method, higher amounts of water are usually added then up to 15 wt %, most often 7 to 10 wt % of water is added. Preferably, the water is added gradually, and most preferably, the water is added by spraying.

[0073] In a particular embodiment, the process of the invention (any of the processes described above) comprises a step of adding elemental sulphur, more particularly molten elemental sulphur (eg at 140°C).

[0074] In the same or another embodiment, the method of the present invention (any of the above methods) includes the step of adding micronutrients. Preferred micronutrients in the context of the present invention are micronutrients containing boron, zinc, manganese, nickel, molybdenum, copper, iron, chloride, sodium, iodine or a combination thereof, etc. Preferred are those containing boron, zinc, manganese, nickel, molybdenum, copper, iron, iodine or a combination thereof (any combination of these).

[0075] Micronutrients can be added at different stages of the production process. They can be added to the hot potassium sulfate just after leaving the muffle, for example just after leaving the cooling drum after the muffle, they can be added after production but before granulation, during granulation, or finally they can be added to the coating.

[0076] The compaction step in method (I) is preferably before the pre-compacting step because it increases the hardness. The granulation step in method (II) is preferably before the step of enhancing the formation of seed crystals. The pretreatment in method (II) is generally composed of 2 steps. The first step may include crushing and / or screening the mixed feed material to reduce the particle size to at most 1000 μm, 900 μm, 800 μm, 700 μm, 600 μm, preferably at most 500 μm, 400 μm, most preferably at most 300 μm (see above). Therefore, fine powder is generally formed. Devices that can be used for crushing are, for example, hammer mills, pin mills, etc. The second step of the pretreatment generally includes a mixing step, which is particularly useful when using a variety of starting materials. For this reason, a plow shear mixer, a paddle mixer, a spiral mixer, etc. can be used. This pretreatment generally results in the formation of some front seed crystals. The pre-seeded mixture is then transferred to a wet granulator, typically a wet drum granulator.

[0077] Suitable wet drum granulators for method (II) include disc, drum, pan granulators and a series of similar devices. In the drum granulator, particles move by the tumbling action caused by the balance between gravity and centrifugal force. Usually preferred disc and pan granulators. The angle of inclination (°), speed (rpm) and depth (cm) of the disc or pan will affect the size, consistency and hardness of the particles obtained. Those skilled in the art will be able to set these parameters to obtain the desired final product.

[0078] Various types of compactors can be used in method (I), but typical roller compactors are preferred. A 10 mm to 15 mm thick plate is then typically formed, which is then crushed with a hammer and / or grid granulator to form granules. As mentioned above, a pre-compacting step is preferably used, especially when a roller compactor is used.

[0079] After granulation, the granules usually still need to be dried because their moisture content and strength are not up to standard.

[0080] The drying of the particles in step (iv) of method (II) is usually carried out with hot air and / or hot gas. Drying can be carried out in a drum dryer, a drum dryer and / or a fluidized bed dryer. Most typically, the drying step is carried out in a fluidized bed.

[0081] The dried granules are then usually sent to a cooler, most commonly by a belt conveyor, to cool to near room temperature (20°C-25°C), thereby increasing the strength of the granules and even further reducing their water content. Sometimes conveying by a belt conveyor is sufficient in itself to cool the dried granules. In other cases, cooling can be carried out in the same fluidized bed dryer used for drying in a second zone with cold air.

[0082] Optionally, the method of the invention (any of the methods described above) may further provide the step of providing one or more coatings. Examples of coatings that may be provided are given above.

[0083] Optionally, the method of the present invention (any of the above methods) also includes polishing and / or post-treatment steps, including but not limited to glazing, further drying, oiling and / or waxing. These steps help to reduce, for example, dust content and increase the hardness of the particles.

[0084] Possibly, the process according to the invention (any of the processes described above) also contains a step for removing the dust formed, for example by means of a fluidized bed or a cascade system with wash plates in combination with cloth filters.

[0085] Optionally, the method of the present invention (any of the methods described above) may further comprise the step of rounding the obtained particles to increase flowability.

[0086] Optionally, the method of the invention (any of the methods described above) comprises a further step of screening to remove any material of undersize or oversize, prior to a possible finishing step, polishing step or post-treatment step.

[0087] Typically, the sieving step comprises one or more sieving steps to retain particles of a desired size. In the context of the present invention, sieving or screening is intended to retain particles with a size of 1 mm to 6 mm, preferably 2 mm to 4 mm. Preferably, at least 90% by weight of the particles have a size of 1 mm to 6 mm, preferably 2 mm to 4 mm.

[0088] Undersized particles can be added back to the feed of salt (A) and / or (B). Oversized particles can also be used again, usually after a crushing and / or sieving step, so that the particle size does not exceed 1000 μm, 900 μm, 800 μm, 700 μm, 600 μm, preferably does not exceed 500 μm, 400 μm, and most preferably does not exceed 300 μm. Usually the material is passed through a number of sieves of different sizes to obtain smaller particle sizes.

[0089] The fertilizer in granular form that can be obtained by the method of the present invention generally has a particle size of 1 mm to 6 mm, preferably 2 mm to 4 mm. Preferably, more than 90% of the particles (by weight) have a size of about 1.5 mm to about 5 mm. More preferably, more than about 95% of the particles (by weight) have a particle size of about 1.5 mm to about 5 mm. Most preferably, there is a range of at least about 80%, 85%, 90% (by weight) between about 2 mm and about 4 mm.

[0090] The hardness of the particles obtained is preferably about 2.0 kg, 2.1 kg, 2.2 kg, 2.3 kg or more, more preferably a hardness of 2.4 kg, 2.5 kg or more, more preferably about 3 kg or more. The hardness of the particles is most preferably at least 3.5 kg, 4 kg, 4.5 kg or even 5 kg. The abrasion of the particles obtained is typically at most 15 weight%, at most 10 weight%, preferably at most 5 weight%. More typical hardness and abrasion values ​​can be found above.

[0091] The on-grade product (or on-grade granules of the present invention) is then typically packaged or stored. Storage on concrete floors is possible, although storage in silos may be preferred prior to shipping (including bulk shipping) or prior to packaging.

[0092] The granules of the present invention are very suitable for use with another type of granular fertilizer, such as N, S, P or K fertilizer (different from the fertilizer of the present invention). Preferably, the granules of the present invention have an SGN number (Size Guide Number) that differs from the granules of N, S, P or K fertilizer by at most 15, preferably at most 10.

[0093] Therefore, another aspect of the invention relates to a (solid) fertilizer comprising a fertilizer in granular form according to the invention and at least one of the following: ammonium nitrate, calcium ammonium nitrate, ammonium sulfate, monoammonium phosphate, diammonium diphosphate, urea, phosphogypsum, single superphosphate, triple superphosphate, fertilizers providing one or more micronutrients such as zinc, iron, boron, manganese, molybdenum and / or copper, multi-nutrient fertilizers such as binary fertilizers (NP, NK, PK) and NPK fertilizers.

[0094] The fertilizer of the present invention can be applied to a variety of food crops, including fruits and vegetables, rice, wheat and other cereals, sugar, corn, soybeans, palm oil and cotton, all of which benefit from the supply of potassium. The fertilizer of the present invention is also suitable for crops that are not tolerant to high chloride sensitivity, such as hops, tobacco, potatoes, many fruits and berries, early-growing vegetables, all greenhouse crops, flowers, seedlings and transplants.

[0095] The measurement methods used in the present invention include the examples.

[0096] - The colour was measured by means of a colorimeter (Minolta CR 310 model).

[0097] - The K content in the examples was determined by constant volume NaTPB method (ISO 5310, AOAC 958.02) and recalculated as K2O.

[0098] - S content was determined via XRF (X-ray fluorescence) and recalculated as SO3.

[0099] - Determination of Cl content via AgNO3 titration.

[0100] - Mg and Ca contents were determined via ICP-OES (Inductively Coupled Plasma - Optical Emission Spectroscopy) and recalculated to MgO and CaO, respectively.

[0101] - Particle size analysis: The particles are sieved on several sieves and the respective fractions (based on weight) are measured.

[0102] -The hardness (or crushing strength) of the granules was measured using a standard test method for the hardness of fertilizer granules. In this article, a commercial compression tester (Indelco 201-M model) was used to measure the hardness. A sample of the granular product was sieved to obtain granules with a diameter of about 3 mm. The individual granules were then placed on a flat surface and pressure was applied by a flat-ended rod connected to the compression tester. The force required to break the granules was measured (expressed in kg). The reported value is the average of 20 individual granules.

[0103] - The abrasion resistance of the granules is measured as follows: 100 g of granules without particles smaller than 0.63 mm are placed in a tube (length 40 cm and diameter 4 cm) and tumbled at 40 rpm for 1 hour. Finally, the granules are sieved and the fraction smaller than 0.63 mm is measured. The lower this fraction < 0.63 mm, the higher the abrasion resistance of the granules (and vice versa).

[0104] The water content is determined gravimetrically by measuring the weight loss of the granules after heating up to 105°C until constant weight, for example by keeping the granules in a laboratory oven, typically at 105°C for 1 hour or at 80°C overnight.

[0105] The present invention is further described and illustrated in detail in the following examples, which are not intended to be limiting in any way. Example

[0106] Material preparation

[0107] Polyhalite (Salt B): used in the following forms: (i) untreated coarse powder, (ii) crushed and sieved at 300 μm, (iii) crushed and calcined.

[0108] Potassium sulfate (Salt A): Used in the following forms: as hot potassium sulfate in powder form just out of the muffle furnace (at 200°C), (ii) as potassium sulfate with a size of less than 500 μm or less than 300 μm (at room temperature).

[0109] Calcination: Calcine the polyhalite at 600°C in a laboratory oven

[0110] Granulation: A series of tests were conducted using polyhalite and a combination of polyhalite and potassium sulfate.

[0111] Granulation was carried out in a disc granulator: Briefly, 1000 g of salt (A) and 1000 g of salt (B) were mixed in a pin mixer for a few minutes to homogenize the salts. The material was then transferred to a rotating disc granulator with an angle set between 40° and 60°. About 10% of water was used as a binder and was added stepwise in a semi-continuous manner. Prior to analysis, the granules obtained were dried in an oven at 80°C for 4 hours. To determine the particle size distribution, the granules were sieved (2 mm-4 mm).

[0112] Examples 1R-3R and Examples 4-8

[0113] A series of tests were carried out using a disc granulator to obtain flowable granules using polyhalite alone on the one hand and in combination with SOP (Salts B and A, respectively) on the other hand. Hardness, abrasion, flowability and particle size distribution were compared (Table II). Granules SOP were used herein as reference.

[0114] Granulation of pure polyhalite (PH) without pretreatment resulted in poor hardness, most likely due to the coarse structure of the raw material. The combination of PH and SOP resulted in an overall higher hardness compared to pure PH. Crushing, sieving and calcining increased hardness and / or wear resistance.

[0115] Where pure SOP granules are free flowing, this is not the case with pure PH granules. The addition of SOP improves flowability and produces a fertilizer with a more balanced nutritional composition. Among others, the granular fertilizer of the present invention is widely applicable due to its free flowing nature and low chloride content. Furthermore, the particle size distribution is more easily controlled than with polyhalite alone. Additionally, the granular fertilizer of the present invention can be easily combined with other types of solid fertilizers standard in the art.

[0116] Similar results were obtained with uraninite and anhydrous philaluminate.

[0117] Table I: Composition of Salt B

[0118]

[0119] The fertilizer in granular form according to the invention is also produced by the compaction method (I). The granule hardness varies from 1 kg to 3 kg, but in general, the granule hardness is > 2 kg. The attrition in this case is < 3%. K 2 O levels were close to 32%-33% (Table II).

[0120] Table II: Tested materials and their properties

[0121]

[0122] PH = polyhalite, SOP = potassium sulfate, hot SOP at 200: SOP just out of the muffle furnace

Claims

1. A fertilizer in granular form, said fertilizer comprising in the same granule a mixture of: based on the total amount of salt, Salt (A) 15 to 85 wt % potassium sulfate; and Salt (B) 85 wt % to 15 wt % of at least one salt; wherein the salt (B) is selected from calcined polyhalite, The granular fertilizer has - a potassium level of at least 18% by weight, expressed as K2O; - a chloride level of up to 10% by weight; and - magnesium levels expressed as MgO of up to 10% by weight, The total amount of the salts is the total amount of salt (A) and salt (B).

2. The fertilizer of claim 1, wherein the potassium level is at least 20% by weight.

3. The fertilizer of claim 1, wherein the chloride level is at most 5 wt%.

4. The fertilizer of claim 1, wherein the chloride level is up to 3 wt%.

5. The fertilizer of claim 1, wherein the magnesium level is up to 9.5% by weight.

6. The fertilizer according to claim 1, having a magnesium level expressed as MgO of at most 9% by weight.

7. The fertilizer according to any one of claims 1 to 6, having a K2O / MgO ratio of at least 3.

8. The fertilizer according to claim 7, wherein the K2O / MgO ratio is at least 3.

2.

9. A fertilizer according to any one of claims 1 to 6, having a potassium level expressed as K2O of at least 25% by weight.

10. The fertilizer of claim 9, wherein the potassium level is at least 30% by weight.

11. The fertilizer according to any one of claims 1 to 6, comprising at least 20% by weight of salt (A), based on the total amount of salt.

12. The fertilizer according to any one of claims 1 to 6, comprising 20 to 80 wt% of salt (A) and 80 to 20 wt% of salt (B), based on the total amount of salt.

13. The fertilizer according to any one of claims 1 to 6, having an average hardness of at least 2 kg and an average abrasion of at most 5% by weight.

14. The fertilizer of claim 13, wherein the average hardness is at least 2.5 kg.

15. The fertilizer according to any one of claims 1 to 6, further comprising at least one micronutrient comprising boron, zinc, manganese, nickel, molybdenum, copper, iron or a combination thereof, and / or further comprising elemental sulfur and / or further comprising one or more dyes.

16. The fertilizer according to any one of claims 1 to 6, having one or more coatings.

17. The fertilizer of any one of claims 1 to 6, wherein at least 90% by weight of the particles have a particle size of 1 mm to 6 mm.

18. The fertilizer of claim 17, wherein at least 90% by weight of the particles have a particle size of 2 mm to 4 mm.

19. A compaction method (I) for preparing a fertilizer in granular form according to any one of claims 1 to 18, comprising the following steps: (i) providing a mixture comprising, based on the total amount of the salts, 15 to 85 wt % of potassium sulfate as salt (A) and 85 to 15 wt % of at least one salt as salt (B); wherein the salt (B) is selected from calcined polyhalite, (ii) optionally, adding a binder; and mixing; (iii) compacting the mixture of step (i) or (ii) in a compactor to obtain granules; (iv) sieving the granules thus obtained to retain granules having a particle size between 1 mm and 6 mm, The total amount of the salts is the total amount of salt (A) and salt (B).

20. The method of claim 19, wherein the binder is a binder comprising water.

21. The method according to claim 19, wherein the mixing is carried out until a homogeneous mixture is obtained again.

22. The method according to claim 19, wherein the particles thus obtained are sieved to retain particles having a particle size between 2 mm and 4 mm.

23. A granulation process (II) for preparing a fertilizer in granular form according to any one of claims 1 to 18, comprising the following steps: (i) providing a mixture comprising, based on the total amount of the salts, 15 to 85 wt % of potassium sulfate as salt (A) and 85 to 15 wt % of at least one salt as salt (B); wherein the salt (B) is selected from calcined polyhalite, (ii) adding water and, optionally, further binders; (iii) mixing; (iv) forming granules of a desired size in a granulator; (v) drying the particles; (vi) optionally, sieving the particles thus obtained to retain particles having a particle size of 1 mm to 6 mm, The total amount of the salts is the total amount of salt (A) and salt (B).

24. The method according to claim 23, wherein the mixing is carried out until a homogeneous mixture is obtained again.

25. The method of claim 23, wherein the granulator is a wet drum granulator.

26. The method according to claim 23, wherein the particles thus obtained are sieved to retain particles having a particle size of 2 mm to 4 mm.

27. The process according to any one of claims 19 to 26, wherein at least 90% by weight of the total amount of salts (A) and (B) provided in step (i) has a particle size of not more than 500 μm.

28. The process according to claim 27, wherein at least 90% by weight of the total amount of salts (A) and (B) provided in step (i) has a particle size of not more than 300 μm.

29. The method according to any one of claims 19 to 26, further comprising at least one of the following steps: - Addition of micronutrients and / or elemental sulphur; - providing one or more coatings; - rounding of the particles; - glazing the particles.

30. The method according to claim 29, wherein the polishing is oiling and / or waxing.

31. A solid fertilizer comprising the fertilizer in granular form according to any one of claims 1 to 18 and at least one further solid fertilizer different from said fertilizer.

32. The solid fertilizer according to claim 31, wherein the at least one additional solid fertilizer different from the fertilizer is selected from ammonium nitrate, ammonium sulfate, ammonium phosphate, diammonium phosphate and / or urea.

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