WO2021250220A1

WO2021250220A1 - Spherical fertilizers and processes for the production thereof

Info

Publication number: WO2021250220A1
Application number: PCT/EP2021/065727
Authority: WO
Inventors: Peter Luts; Peter Landuyt; Kristof GILS
Original assignee: Tessenderlo Group Nv
Priority date: 2020-06-10
Filing date: 2021-06-10
Publication date: 2021-12-16

Abstract

The present invention relates to a process for making a fertilizer in granular form, said process comprising: (i) Providing a mixture comprising (a) potassium sulfate (A) and (b) one or more binders, said one or more binders including water, wherein at least 30 wt.%, preferably at least 40 wt.% of said potassium sulfate (A) has a particle size between 75 and 1000 µm; (ii) Subjecting the mixture to a granulation step to form granules, preferably wherein said granulation step is effected in a wet tumbling granulator; and (iii) Drying the granules; and (iv) Optionally, sieving of the granules thus obtained to retain granules that have a particle size between 1 and 6 mm, preferably between 2 and 5 mm.

Description

SPHERICAL FERTILIZERS AND PROCESSES FOR THE PRODUCTION THEREOF

FIELD OF THE INVENTION

[0001] The present invention relates to the field of fertilizers, more in particular to the field of granular fertilizers with high K (potassium) content and low chloride (Cl ) content having the shape of a sphere. Fertilizers of the invention have a good balance of at one hand hardness and at the other hand wear resistance.

BACKGROUND OF THE INVENTION [0002] Fertilizers are well known for agricultural and horticultural application. A number of nutrients are thereby supplied to the soil or growing medium of the plants. Nutrients such as nitrogen, phosphorous, potassium, calcium, magnesium and sulfur are supplied in relatively large amounts, while many other elements are supplied in lower amounts, as micronutrients.

[0003] Solid fertilizers exist in the form of granules, prills, powder and crystals. SOP (sulfate of potash) is primarily sold as granular fertilizer and is often combined (via bulk blending) with other fertilizers such as an N or P fertilizer.

[0004] Farmers want K fertilizers that are easy to spread on the field together with N or P fertilizers. The fertilizer industry wants products that are free flowing, that are easy to pack, store and transport and that present low segregation. When particles have a good hardness and wear resistance, then particles will break less easily and will be easier to coat.

[0005] The industry continuously looks for new forms of K fertilizers with a good nutrient balance, high enough K content and low enough chloride content.

[0006] WO 2017163246 (Dead Sea Works ltd) discloses spherical fertilizer granules having a specific gravity of more than 1.94 g/cm³ and less than 3% porosity. Described therein is a one- step compaction process for making spherical MOP (Muriate of Potash) granules via roller compaction having spherical cavities and soft crushing, starting from MOP dust. When this method was tested for SOP (Sulfate of Potash), particles tended to stick to the rollers and the spherical cavities therein. Particles formed were also too coarse. SUMMARY OF THE INVENTION

[0007] The invention provides a process for making a fertilizer in granular form, said process comprising:

(i) Providing a mixture comprising (a) potassium sulfate (A) and (b) one or more binders, said one or more binders including water, wherein at least SO wt.%, preferably at least 40 wt.% of said potassium sulfate (A) has a particle size between 75 and 1000 pm;

(ii) Subjecting the mixture to a granulation step to form granules, preferably wherein said granulation step is effected in a wet tumbling granulator; and

(iii) Drying the granules; and

(iv) Optionally, sieving of the granules thus obtained to retain granules that have a particle size between 1 and 6 mm, preferably between 2 and 5 mm.

[0008] The invention further provides a granular fertilizer obtainable by the process according to the invention.

[0009] The invention further provides a granular fertilizer characterized by the following: a potassium sulfate content of from 20 to 100 wt%, preferably from 50 to 100 wt%, relative to the total of salts in the fertilizer, a chloride level of at most 10 wt%, preferably at most 5 wt%,

70 wt% or more of the granules have a particle size between 1 and 6 mm, preferably between 2 and 5 mm, more preferably size between 2.5 and 4mm, a granule hardness of at least 2.7 kg, typically at least 3 kg, and a granule wear of at most 7 wt%, preferably at most 5 wt%, more preferably at most 2 wt%.

DETAILED DESCRIPTION

[00010] The invention provides a granular fertilizer characterized by the following: a potassium sulfate content of from 20 to 100 wt%, preferably from 50 to 100 wt%, relative to the total of salts in the fertilizer, a chloride level of at most 10 wt%, preferably at most 5 wt%, 70 wt% or more of the granules have a particle size between 1 and 6 mm, preferably between 2 and 5 mm, more preferably size between 2.5 and 4mm, a granule hardness of at least 2.7 kg, typically at least 3 kg, and a granule wear of at most 7 wt%, preferably at most 5 wt%, more preferably at most 2 wt%.

[00011] The term 'wt%' herein stands for 'weight percentage' or 'percentage by weight'. Below details on preferred compositions and preferred features of the granular fertilizers of the invention, any of the above.

[00012] It is an aim of the invention to provide a granular fertilizer that is free flowing and considered to be "round", "spherical" or "pseudo-spherical". The terms "sphere" and/or

"spherical" and/or "pseudo-spherical" as used herein refer to any round geometrical object in three-dimensional space, e.g., having the shape of a round or elliptic ball.

[00013] The granular fertilizer or "fertilizer in granular form" of the invention may be quite uniform, both with regard to size & shape. The granular fertilizer of the invention in general has a smooth surface, a homogeneous and uniform size and does not require substantial rounding. [00014] A "spherical" or "pseudo-spherical" shape can improve the resistance of the granule against deterioration & may improve the strength of the granule and prevent dust formation. Yet for SOP (Sulfate of Potash) based materials such characteristics are not easy to obtain, in particular when a potassium sulfate is being blended with salts other than KCI (Muriate of Potash, MOP).

[00015] We were able to obtain a granular fertilizer with in general 80 wt% or more of the granules having a sphericity of 0.8, when measured with a Microtac Camsizer (Da>lmm, LW- ratio<5). Preferably, this amount is at least 81, 82, 83, 84, 85, 86, 87, 88, 89, 90 wt% or more. Preferably at least 85 wt% or more, preferably at least 90 wt% or more of the granules have a sphericity of 0.9.

[00016] Preferably at least 70, 75, 80, 85, even at least 90 wt% or more of the granules obtained have a particle size between 1 and 6 mm, preferably between 1 and 5 mm. Most preferably at least 95, 96, 97, 98 wt% of the particles have a particle size between 1 and 5 mm, preferably between 2 and 5 mm. [00017] In an embodiment of the invention, the fraction with a size between 1 and 4 mm is from 30 to 70 wt%, from 35 to 70 wt%, more preferably from 40 to 70 wt%, most preferably from 50 to 70 wt%. In another embodiment of the invention, the fraction with a size between 1 and 4 mm is from 50 to 99 wt%, more preferably from 55 to 95 wt%. In a particular embodiment of the invention, 90 wt% or more of the granules have a particle size between 2 and 4 mm.

[00018] In a preferred embodiment, 70 wt% or more of the granules have a particle size between 2.5 and 4mm. Preferably this percentage is at least 75, 80, 85, 86, 87, 88, 89, 90 wt% or even more. In the same or another preferred embodiment, the d50 (in mm) preferably is between 3 and 3.5 mm.

[00019] In a preferred embodiment of the invention, less than 15 wt%, preferably less than 10 wt% of the granules have a particle size below 1 mm. Preferably, less than 1 wt%, more preferably less than 0.5 wt%, most preferably less than 0.3 wt% of the granules have a particle size below 1 mm. Preferably less than 5 wt%, more preferably less than 1.5 wt%, even more preferably less than 1 wt% have a particle size above 5 mm.

[00020] The potassium sulfate (K2SO4, also called Sulfate of Potash, or SOP) can be derived from mined minerals or be prepared in a muffle furnace. In some embodiments of the invention, it may be preferred to use a potassium sulfate (A) that is produced via a Mannheim process, in a muffle furnace.

[00021] The potassium sulfate content typically is from 20 to 100 wt%, relative to the total weight of salts in the fertilizer. Preferably, the amount of potassium sulfate (A) is at least 30, 35, more preferably at least 40, 45, 50 wt% of potassium sulfate (A), relative to the total weight of salts in the fertilizer. In a particular embodiment of the invention the amount of potassium sulfate (A) is at least 60, 65, 70, 75, 80, 85, even at least 90, 91, 92, 93, 94, 95 wt% or even more of potassium sulfate, relative to the total weight of salts in the fertilizer.

[00022] It is possible e.g. to blend the potassium sulfate (A) with at least one salt (B) is different from (A) like a magnesium sulfate, possible a magnesium double salt.

[00023] When salts (B) are blended with the potassium sulfate (A) then it is preferred to have, relative to the total weight of salts in the fertilizer, from 20 to 80 wt% of salts (A) and from 80 to 20 wt% of salts (B). More preferably, there is from 30 to 70 wt% of salts (A) and from 70 to 30 wt% of salts (B), relative to the total weight of salts in the fertilizer. Most preferably, there is from 40 to 60 wt% of salts (A) and from 60 to 40 wt% of salts (B), relative to the total weight of salts in the fertilizer. In a preferred embodiment of the invention, the sum of A+B, relative to the total weight of salts in the fertilizer, is at least 80, 85, 90, 95, 96, 97, 98, or 99 wt%. Obviously, a sum of more than 100 wt% is not possible.

[00024] In the context of the present invention, whenever the total weight of salts, or the weight of a specific salt or mineral is referred to, this should be interpreted to include the weight of the water of hydration in case any of the salts or minerals are provided in hydrated form.

[00025] When one or more salts (B) are blended with the potassium sulfate (A), then preferably both are distributed more or less homogeneously over the fertilizer granule. In some embodiments the granule may be provided in the form of a coated granule having a core wherein the one or more salts (B) and the potassium sulfate (A) are distributed homogenously, and comprise one or more coating layers wherein the one or more salts (B) and the potassium sulfate (A) are not distributed homogenously, or are absent.

[00026] Whether blended or not with one or more salts (B), it is preferred in the context of the invention that the potassium sulfate content is at least 40, 45, 50 wt%, preferably at least 70 wt%, more preferably at least 90 wt%, relative to the total weight of salts in the fertilizer. In a particular embodiment of the invention, the potassium sulfate content, relative to the total weight of salts in the fertilizer, is at least 90 wt%, preferably at least 95, 96, 97, 98, 99 wt%. In an embodiment of the invention, salts (B) are present, preferably in an amount of at least 10 wt%, relative to the total weight of salts in the fertilizer. In another embodiment of the invention, no salts (B) are present. In a particular embodiment of the invention, apart from some impurities possibly present in salts (A), no other sulfate salts are being admixed, such that the amount of sulfate salts other than potassium sulfate (A) is less than 5 wt.%, 4 wt.%, 3 wt.%, 2 wt.% or 1 wt.%, relative to the total weight of salts in the fertilizer.

[00027] In a preferred embodiment of the invention, the potassium sulfate content is from 20 to 100 wt%, relative to the total weight of the fertilizer. Preferably, the amount of potassium sulfate (A) present is at least BO, 35, more preferably at least 40, 45, 50 wt% of potassium sulfate (A), relative to the total weight of the fertilizer. In a particular embodiment of the invention the amount of potassium sulfate (A) present is at least 60, 65, 70, 75, 80, 85, even at least 90 wt% or more, relative to the total weight of the fertilizer.

[00028] To have a balanced nutrient composition, the following is aimed for in particular:

- the potassium level (expressed as K2O) preferably is at least 25 wt%, preferably at least 30, 35, 40 wt%, in a particular embodiment of the invention this level is at least 50 wt%.

- The magnesium level (expressed as MgO) typically is from 0 to at most 10, at most 9.9, 9.8, 9.7, 9.6 wt%, more preferably at most 9.5, 9.4, 9.3, 9.2, 9.1 or 9 wt%. When for instance a potassium magnesium salt and/or a potassium calcium magnesium salt is present as salt (B), then typically the magnesium level is at least 0.05 wt%, preferably at least 0.1 wt%. Preferably, the foO/IVIgO ratio (expressed as wt% ratio) is then 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 and more.

- The calcium level (expressed as CaO) typically is from 0 to at most 10, 9.9, 9.8, 9.7, 9.6 wt%, more preferably at most 9.5, 9.4, 9.3, 9.2, 9.1 or 9 wt%. When for instance a potassium calcium magnesium salt is present as salt (B), then typically the calcium level is at least 0.05 wt%, preferably at least 0.1 wt%. In a particular embodiment, the calcium level is at least 1, 1.5, 2, 2.5 wt%. In the same or another embodiment, the calcium level is at most 5, 4.5, 4 wt%.

- The sulfate level (expressed as S0₃) of the fertilizer in granular form preferably is from 40 to 55 wt%, preferably from 40 to 50 wt%.

- The chloride level preferably is at most 9 wt%, more preferably at most 5 wt% and most preferably at most 3 wt%.

[00029] Apart from the salts (A) and (B) the granules of the invention may further contain a binder, like a grinding binder or a binder containing materials that improve cohesion and/or hardness. Such binder may be of organic and/or of inorganic nature. Such binder may contain one or more of the following ingredients: water, chalk, sodium silicate, potassium silicate, fly ash, geopolymers, starch, cellulose gums, sucrose, lignosulfates, molasses, magnesium oxides, calcium oxides, lime, hydrated lime [Ca(OH)2], bitumen, Portland cement, alganite, clays like bentonite, acids (nitric, hydrochloric, phosphoric, sulfuric acid), oils, waxes and the like. In particular the use of lime and/or of hydrated lime, all than not in combination with a(nother) hydroxide like chalk was found to improve particle hardness. Also SOP solutions, for instance 10-15 wt% solutions of SOP (salt A) in water, proved to a have a positive effect on particle hardness. The same with solutions in water of a salt B (examples above), from which preferably insoluble materials were removed.

[00030] Apart from the salts (A) and (B) and optionally a binder, the granules of the invention may further comprise other additives and coatings.

[00031] Examples of additives that may be added include dyes, pH aids, (elemental) sulfur, extra macronutrients or micronutrients that contain boron, zinc, manganese, nickel, molybdenum, copper, iron, chloride, sodium, iodine or combinations thereof, etc. Preferred are those that contain boron, zinc, manganese, nickel, molybdenum, copper, iron, iodine or combinations thereof (of any of these). Additives can be added during or after production. Possibly they can be provided in the form of a coating.

[00032] The granules of the invention can also contain one or more coatings. The coating can be an antidust-coating and/or an anti-caking coating and/or a slow or controlled release coating and/or a coating that contains additional nutrients. Also possible are biodegradable coatings and/or oily coatings or waxy coatings that reduce dustiness.

[00033] Preferably, the granules of the invention have been polished or post-treated, and are waxed, oiled, glazed or the like to increase hardness and/or to reduce dustiness. Any oil (e.g. mineral oil) or any wax (e.g. slack wax, paraffin wax) standard in the art may be used to improve rheology and/or to decrease dustiness.

[00034] Advantageously, granules of the invention (or the fertilizer in granular form of the invention) on average have a hardness of at least 2, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7 kg. Typically the hardness is at least 2.7 kg. Preferably, the hardness is at least 2.8, 2.9 or at least 3 kg. The hardness of the granules preferably is at least 3.5, 4, 4.5 or even 5 kg. The granules of the invention (or the fertilizer in granular form of the invention) have on average a wear of at most 15, 14, 13, 12, 11, 10, 9, 8, 7 wt%, preferably at most 6.5, 6, 5.5. It is preferred that the wear is at most 5, 4.5, 4, 3.5 wt%. Most preferably, the wear is at most 3, 2, 1 wt%. In a particular embodiment, the wear is at most 0.5 wt%, even at most 0.3 wt%.

[00035] Preferably the granular fertilizer of the invention is characterized by the following:

A hardness of at least 2.7, 2.8, 2.9, 3, 3.5, 4, 4.5 or even 5 kg and/or - A wear of at most 5, 4.5, 4, 3.5, 3, 2, 1, 0.5 or even at most 0.3 wt%.

[00036] Typically, the granular fertilizer, when 1 gram is dissolved in 100 ml of water, exhibits a pH of between 2 and 7, preferably 2 and 6.

[00037] Typically, the granular fertilizer of the invention has a porosity as measured with a mercury intrusion process of at least 7 wt%, preferably at least 10 wt%. [00038] The granules were found to be sufficiently round and free flowing. With the methods described below it is possible to obtain a spherical fertilizer.

[00039] The fertilizer in granular form of the invention, can be made in various ways.

Typically, the granules of the invention are produced either through compaction or through a granulation process based on size enlargement, such as a wet tumbling granulation. [00040] Granulation is a size enlargement operation by which a fine powder or finer material is agglomerated into larger granules in order to produce a specific size and shape, to improve flowability and appearance and to reduce dustiness. Size enlargement herein is preferably via tumble growth. Both dry and wet granulation exist but in the present context, a wet granulation and more in particular a wet tumbling granulation is preferred. [00041] The fertilizer according to the invention may be prepared by a process (I) for making a fertilizer in granular form, said process comprising:

(i) Providing a mixture comprising (a) potassium sulfate (A) and (b) one or more binders, said one or more binders including water, wherein at least 30 wt.%, preferably at least 40 wt.% of said potassium sulfate (A) has a particle size between 75 and 1000 pm;

(iii) Drying the granules; and (iv) Optionally, sieving of the granules thus obtained to retain granules that have a particle size between 1 and 6 mm, preferably between 2 and 5 mm.

[00042] It is also possible to produce the fertilizer according to the invention by a compaction process (II) that comprises the steps of:

(i) Providing (a) potassium sulfate (A) and, optionally, (b) at least one salt (B) that is different from (A) and that provides potassium and/or magnesium and/or calcium and/or sulfate, in such amounts that the resulting granular fertilizer has

- a chloride level of at most 10 wt%, preferably at most 5 wt%, and

- a potassium sulfate content of from 20 to 100 wt%, relative to the total of salts in the fertilizer;

(ii) Optionally, adding a binder, preferably a binder that comprises water; and mixing until a homogeneous mixture is obtained;

(iii) Compacting said mixture in a compactor, preferably a plaque compactor, and obtaining granules;

(iv) Sieving of the granules thus obtained to retain granules that have a particle size between 1 and 6 mm, preferably between 2 and 5 mm.

[00043] Examples of granulators that can be used in the process (I) include but are not limited to tumbling granulators including disc, drum, pan granulators, rotary drum granulators, gear and rotary drum granulators and the like. Another word for "granulator" is "pelletizer". Though spray and melt granulation theoretically could be used too, it is less preferred in the context of the present invention. Best results were obtained with tumbling granulators including disc, drum and pan granulators.

[00044] Below, preferred ways of operation are provided. What is mentioned below in general applies to any process of the invention [any process (I) or any process (II) as described herein], unless indicated otherwise.

[00045] In a preferred embodiment, the process of the invention (any of the above) is a continuous or semi-continuous process wherein oversized and undersized particles can re-enter the system. Oversized particles are herein typically subjected to the proposed pre-treatments to reduce particle size (see infra). Oversized and undersized particles as referred herein can be the same as or be different from oversized and undersized particles in the recyclate (A') as defined above.

[00046] Optimally, the feed material that is used in a method of the invention (any of the above) has a particle size of at most 1000, preferably of at most 500 pm. If a size reduction is needed to arrive at the preferred particle size then this preferably done prior to the adding of water. A size reduction, if needed, can be done for each of the feed materials independently or after their admixture, whatever is most convenient.

[00047] With a method of the invention (any of the above), typically 70 wt% or more of the granules that are obtained have a particle size between 1 and 6 mm, preferably between 2 and 5 mm. With the methods of the invention it is possible to obtain a granular fertilizer with a d50 (in mm) between 3 and 3.5 mm. Preferred particle sizes and particle size distributions have been given above. Typically less than 15 wt% of the granules need a further shaping or rounding. Preferably this percentage is less than 10 wt%.

[00048] Information on typical amounts in the fertilizer in granular form of salts (A), and of optional salts (B), defined in relation to the fertilizer of the present invention equally apply to the methods of its production described herein (any of the above).

[00049] The potassium sulfate content of the granules typically is from 20 to 100 wt%, relative to the total of salts in the fertilizer. Preferably, on the total of salts, you have at least 30, 35, more preferably at least 40, 45, 50 wt% of potassium sulfate (A). In a particular embodiment of the invention you have at least 60, 65, 70, 75, 80, 85, even at least 90, 91, 92, 93, 94, 95 wt% of potassium sulfate in the granules, relative to the total of salts.

[00050] Preferably, the amount of potassium sulfate (A) present in the granules obtained is at least 30, 35, more preferably at least 40, 45, 50 wt% of potassium sulfate (A), relative to the total weight of the fertilizer. More preferably, the amount of potassium sulfate (A) present in the granules is at least 60, 65, 70, 75, 80, 85, even at least 90 wt% or more, relative to the total weight of the fertilizer.

[00051] When salts (B) are blended with the potassium sulfate (A) then it is preferred to have, on the total of salts, from 20 to 80 wt% of salts (A) and from 80 to 20 wt% of salts (B). More preferably, you have from 30 to 70 wt% of salts (A) and from 70 to 30 wt% of salts (B). Most preferably, you have from40 to 60 wt% of salts (A) and from 60 to 40 wt% of salts (B). In a preferred embodiment of the invention, the sum of A+B, on the total of salts, is at least 80, 85, 90, 95, 96, 97, 98, or 99 wt%. Obviously, a sum of more than 100 wt% is not possible.

[00052] The potassium sulfate (A) can have the following origin. It can be:

Mined and processed to clean away unwanted salts, or

Produced from the reaction of potassium chloride with sulfuric acid in a potassium sulfate furnace, following e.g. a Mannheim process.

[00053] In some embodiments of the invention, it can be beneficial to use a potassium sulfate (A) that is produced in a potassium sulfate furnace, via the Mannheim process. Alternatively, a potassium sulfate (A) derived from an evaporite mineral can be used. For instance, a potassium chloride can be reacted with various sulfate salts to form a double salt that can then be decomposed to yield potassium sulfate (A). The sulfate salt reacted with the potassium chloride can be a sodium sulfate (in the form of mirabilite and/or sulfate brine) and/or a magnesium sulfate (in the form or kieserite and/or epsomite).

[00054] In a particular embodiment of the invention, the potassium sulfate (A) is at a temperature of between 100 and 400°C; more particular at a temperature between 150 and 400 °C, when it is mixed with salts (B). Such potassium sulfate is referred to herein as a "hot" potassium sulfate. Particularly preferred is a potassium sulfate (A) that has just left cooling drum after the muffle furnace, when it has a temperature of near 200°C or near 300°C. In the same or another embodiment of the invention, the potassium sulfate (A) used has a pH from 2 to 7, preferably from 2 to 4. Typically, the potassium sulfate (A) is not compacted, in other words is not subjected to a pressure agglomeration step. Most typically the potassium sulfate (A') is provided in the form of a powder. It is possible to use in a method of the invention a mixture of 2 different potassium sulfates, referred to herein further as potassium sulfates (A) and as potassium sulfates (A').

[00055] The present inventors have found for instance that it is advantageous to add to a non-compacted potassium sulfate (A) a certain amount of a compacted potassium sulfate (A'), as this improves the overall hardness and general properties of the final product. The compacted potassium sulfate (A') can be provided in any form, as powder and/or as granules and/or as a recyclate (comprising recycled oversized and/or undersized particles).

[00056] Preferably, the compacted potassium sulfate (A') has a hardness of > 3.0 kg, more preferably > 4.0 kg. The hardness of the compacted potassium sulfate (A') may be < 5.0 kg. [00057] Preferably, at least 50 wt.% of the compacted potassium sulfate (A') has a particle size below 500 miti.

[00058] It has been found that the compacted potassium sulfate (A') may take the role of strong seeds for the granulation process.

[00059] As recyclate of the compaction process' (referred as A') may for instance be used particles of a SOP pressure agglomeration process starting from the storage and from further on the particulate qualification step by sieving. The particles may have a size below 2mm and above 4-5mm, and may be smoothly crushed such that the main part of the particle size gets below 500 m with the least possible formation of dust.

[00060] Ideally, the compacted potassium sulfate (A') is crushed and/or sieved before it is added to salts (A) and possible other salts, like salts (B). The following fractions of a recyclate (A') were found highly suitable for use in the present invention: (1) undersized materials that pass a 2mm sieve, or a 1mm sieve and/or (2) oversized materials that do not pass a 6 mm sieve, or a 5 mm sieve but typically are reduced in size prior to use.

[00061] In an embodiment of the invention, the compacted potassium sulfate (A') is obtained via a process wherein a crude potassium sulfate is produced via the Mannheim process followed by a neutralization, at least in part, and then compacting or pressure agglomeration of the neutralized product. Often this step is followed by breaking and then sieving or sieving and then breaking wherein undersized and/or oversized materials are separated from the fraction of granules that have the desired granulometry (see preferred sizes as defined infra). Oversized materials typically are reduced in size, e.g. via a mill or a crusher, prior to use in a method of the invention.

[00062] In an embodiment of the invention, no compacted potassium sulfate (A') is used in a method of the invention. In another embodiment, a compacted potassium sulfate (A') is used, more in particular a recyclate of a compacted potassium sulfate (A').

[00063] Preferably no more than 80 wt% of potassium sulfate (A) provided in step (i) is provided in the form of a compacted potassium sulfate (A') and/or its recyclate. Preferably, no more than 70, 60, 50, 40, 30, 20 wt% of potassium sulfate (A) provided in step (i) is provided in the form of a compacted potassium sulfate (A') and/or its recyclate.

[00064] The compacted potassium sulfate (A') preferably has a particle size of at most 1000 pm, preferably at most 500 pm, more preferably at most 300 pm.

[00065] Preferred salts (B) have been listed above, and as indicated above, salts (B) preferably are used in their calcined form. When not purchased as such, then the process of the invention (any of the above) preferably comprises a calcination step (of salts (B)) prior to the mixing of salts (B) with salts (A). Eventually it is possible to use a mix of partly calcined and partly non- calcined salts (B).

[00066] Whatever salts being used in the context of the invention, it is preferred to start from materials with a size no bigger than 1000, 900, 800, 700, 600 pm, preferably no bigger than 500, 400 pm, more preferably no bigger than 300 pm. This can be achieved by crushing and/or sieving of salts (A) and/or (A') and/or the optional salts (B), where needed. [00067] Crushing machines that can be used include semi-wet material crushers, chain crushers, hammer mill crushers, a pin mill and the like. Sieving in general consists of passing the materials through subsequent sieves, starting for instance at 5 mm and ending with 300 pm. [00068] In an embodiment of the invention, a step of crushing and/or sieving precedes step (i). Usually, a step of crushing and/or sieving follows step (i). Preferably, the step of crushing and/or sieving precedes the step of adding water, and optionally other binder materials. Examples of suitable and preferred binding materials can be found above.

[00069] In an embodiment of the invention, at least 30wt%, preferably at least 35 wt%, more preferably at least 40wt%of the potassium sulfate (A) has a particle size between 75 and 1000 pm. [00070] In an embodiment of the invention, the fraction of salts (A) with a particle size between 100 and 1000 pm is within the range of from 30 to 70 wt%, preferably within the range of from 35 to 70 wt%, more preferably within the range of from 40 to 70 wt%, most preferably within the range of from 50 to 70 wt%. In another embodiment of the invention, the fraction of salts (A) with a particle size between 75 pm and 600 pm is within the range of from 50 to 99 wt%, more preferably within the range of from 55 to 95 wt%. In a particular embodiment of the invention, 90 wt% or more of the granules have a particle size between 50 and 600 pm. Preferably, in any of the above the particle size of the potassium sulfate (A) is at most 600 pm, preferably at most 550 pm, more preferably at most 500 pm. Preferably also the particle size of the salt(s) (B) is at most 600 pm, preferably at most 550 pm, more preferably at most 500 pm to avoid the formation of agglomerates. Preferably, in any of the above the particle size of the potassium sulfate (A) is at least 75 pm, more preferably at least 100 pm. Preferably also the particle size of the salt(s) (B) is at least 75 pm, more preferably at least 100 pm. A size below 50 pm can have a negative impact on the desired properties like hardness if their amount exceeds a certain percentage.

[00071] Product feeds with the abovementioned particle size diameter form depending on the granulator speed, granulator angle and granulator rim height round spherical particles of the abovementioned grain size (preferably 90 wt% or more of the particles have a grain size between 2 and 4 mm). Once these particles have the correct size and weight, they will leave the granulator due to the centrifugal speed, proceeding their way to the drying step.

[00072] If feed particles are too coarse an uncontrolled agglomeration might occur, forming lumps of different shapes, all but not round. These particles will take in mass and will stay in the granulator, disturbing the process.

[00073] Mixing of the salts (A), optionally the salts (B) and possibly further ingredients like a binder (examples above) is straight forward. Any mixer can be used that leads to a more or less homogeneous mixture. The mixer used in a process of the invention (any of the above) can be a horizontal or vertical mixer, a paddle mixer or ploughshare mixer, a turbomixer, a pin mixer or the like. In the granulation method (I) the mixing can be in the granulator, like for instance a pan or a disc pelletizer. Preferred however is to have a (separate) mixing step before the pelletizer.

[00074] The amount of water that is added depends on the production process. The person skilled in the art will know the amount of water to add. For instance, when compaction (II) is used then typically from 0.5 to 3 wt% of water is added. Most typically from 1 to 2 wt% of water is then used. In a wet granulation process (I); more in particular a wet tumbling granulation process, typically a higher amount of water is added, up to maximally 15 wt%, most often from 7 to 12, preferably from 7 to 10 wt% of water is then added. Water preferably is added step-wise, and most preferably, water is added by spraying.

[00075] In a particular embodiment, the process of the invention (any of the above) comprises a step of adding elemental sulfur, more in particular molten elemental sulfur (e.g. at 140°C).

[00076] In the same or another embodiment, the process of the invention (any of the above) comprises a step of adding micronutrients. Preferred micronutrients in the context of the invention are micronutrients that contain boron, zinc, manganese, nickel, molybdenum, copper, iron, chloride, sodium or combinations thereof, etc. Preferred are those that contain boron, zinc, manganese, nickel, molybdenum, copper, iron, or combinations thereof (of any of these). [00077] Micronutrients can be added at various moments along the production process. They can be added to a hot potassium sulfate that just left the muffle furnace, e.g. just left the cooling drum after the muffle furnace, they can be added post production but prior to granulation, during granulation, or eventually they can be added to a coating. [00078] The compaction step in a process (I) preferably is preceded by a step of pre compaction as this increases hardness. The granulation step in a process (II), is preferably preceded by a step that enhances seed formation. Often the pre-treatment in a process (II) consist of 2 steps. A first step may consist of the crushing and/or sieving of the feed materials that were mixed to reduce particle size to at most 1000, 900, 800, 700, 600 pm, preferably at most 500, 400 pm, most preferably at most 300 pm (see above). Hereby a fine powder is typically formed. Devices that can be used for the crushing are e.g. a hammer mill, a pin mill and the like. The second step of this pre-treatment typically comprises a mixing step, useful in particular when multiple starting materials are used. For this purpose plough shear mixers, paddle mixers, screw mixers and the like can be used. This pre-treatment typically results in the formation of some pre-seeds. The mixture with pre-seeds is then transferred to a wet granulator, typically a wet tumbling granulator.

[00079] Suitable wet tumbling granulators for use in a process (II) include disc, drum, pan granulators and a range of similar equipment. In tumbling granulators, particles are set in motion by the tumbling action caused by the balance between gravity and centrifugal forces. Disc and pan pelletizers are generally preferred. Tilt angle (°), speed (rpm) and depth (cm) of the pan or disc have an impact on the size, consistency and also the hardness of the granules obtained. A person skilled in the art will be able to set these parameters to achieve the desired end-product. [00080] Various types of compactors can be used in a process (I) though preferred are the typical roller compactors. Then typically plaques of 10 to 15 mm thick are formed, that are then crushed with a hammer and/or a grid granulator to form granules. As mentioned above, it is preferred to use a step of pre-compaction in particular when a roller compactor is used..

[00081] After granulation the granules typically still need to be dried because their water content and strength cannot reach the standard.

[00082] The drying of the granules in step (iv) of process (II) typically is done with hot air and/or hot gas. The drying can be in a tumble dryer, drum dryer and/or more gently for weaker green pellets (wet pellets) in a fluidized bed dryer. Most typically, the drying step is done in a fluidized bed. The hot air can be produced from natural gas or, in a more sustainable way, one can use recuperated heat from steam, increased in temperature with electricity.

[00083] The dried granules are then usually sent to a cooler, most often by belt conveyor, to cool near room temperature (20-25°C), so that the strength of the granules is improved and their water content is even further reduced. Sometimes transport by belt conveyor suffices in itself to cool down the dried granules. In other instances, cooling can be done in the same fluid bed dryer that was used for drying, in a second zone with cold air.

[00084] Optionally, the process of the invention (any of the above) can further provide a step of providing one or more coatings. Examples of coatings that can be provided are given above. [00085] Optionally, the process of the invention (any of the above) further comprises a step of polishing and/or post-treatment comprising but not limited to glazing, further drying, oiling and/or waxing. These steps help to decrease e.g. dustiness.

[00086] Possibly the process of the invention (any of the above) further contains a step of removing dust that is formed, for example with the aid of a fluidized-bed or a cascade system with wash decks combined with a cloth filter.

[00087] In general, the amount of dust produced is low, typically below 0.5 wt%, below 0.4 wt%, preferably below 0.2 wt%.

[00088] Optionally, the process of the invention (any of the above) can further comprise a step of rounding or spheronizing, the granules obtained to increase the flowability.

[00089] Optionally the process of the invention (any of the above) comprises a further step of screening, to remove any materials that are either undersized or oversized, prior to a possible finishing step, polishing step or post-treatment step.

[00090] Often, the screening step comprises one or more sieving steps to retain particles of the desired particle size. Screening or sieving, in the context of the invention, aims to retain particles that have a particle size between 1 and 6 mm, preferably between 2 and 4 mm. [00091] Undersized and/or oversized particles can be added again to the feed of salts (A) and/or (B), typically before a step of crushing and/or sieving so that the particle size does not exceed 1000, 900, 800, 700, 600 pm, preferably does not exceed 500, 400 pm, most preferably does not exceed 300 pm. Often materials pass multiple sieves of different size to obtain the smaller particle size. [00092] The fertilizer in granular form that can be obtained with a process of the invention typically has a particle size between 1 and 6 mm, preferably between 1 and 5 mm. Preferably, more than 90% of the particles (by weight) have a size between about 1.5 and about 5 mm. More preferably, more than about 95% of the particles (by weight) have a size between about 1.5 and about 5 mm. A range with at least about 80, 85, 90% (by weight) between about 2.0 and about 4 mm is most preferred.

[00093] The hardness of the granules obtained preferably is about 2.0, 2.1, 2.2, 2.3 kg or higher, more preferably the hardness is 2.4, 2.5 kg or higher, more preferably about 3 kg or higher. The wear of the granules obtained typically is at most 15, at most 10 wt%, preferably at most 5 wt%. More typical values of hardness and wear can be found above. [00094] Qualified products (or qualified granules of the invention) are then typically packed or stored. Materials of the invention preferably are stored in silos prior to transport including bulk transport, or prior to packaging.

[00095] Granules of the invention are highly suitable for the use together with another type of granular fertilizer, such as an N, S, P or K fertilizer (different from the one of the invention). Preferably, the granules of the invention have a SGN number (size guide number) that differs at most 15, preferably at most 10 with the granule of the N, S, P or K fertilizer.

[00096] Hence, another aspect of the invention relates to a (solid) fertilizer comprising the fertilizer in granular form of the invention and further at least one of ammonium nitrate, calcium ammonium nitrate, ammonium sulfate, monoammonium phosphate, diammonium diphosphate, ureum, phosphogypsum, single superphosphate, triple superphosphate, fertilizers that provide one or more micronutrients like zinc, iron, boron, manganese, molybdenum and/or copper, multinutrient fertilizers such as binary fertilizers (NP, NK, PK) and NPK fertilizers. [00097] Fertilizers of the invention can be applied to a variety of food crops, including fruits and vegetables, rice, wheat and other grains, sugar, corn, soybeans, palm oil and cotton, all of which benefit from the supply of potassium. The fertilizers of the invention are further suited for use on crops that do not tolerate high chloride sensitive such as hop, tobacco, potato, many fruits and berries, early vegetables, all crops under glass, flowers, seedlings and transplants. [00098] Fertilizers of the invention due to their size and shape are highly suited for use on golf fields.

[00099] Measuring methods, as used throughout the invention, including the Examples section.

- Color was measured via a Colorimeter (type Minolta CR B10).

- K-content in examples was determined via the volumetric NaTPB-method (ISO 5310, AOAC 958.02) and recalculated as K2O.

- S-content was determined via XRF (X-ray Fluorescence) and recalculated as S03

- Cl-content was determined via AgN03-titration.

- Mg- and Ca-content were determined via ICP-OES (Inductively Coupled Plasma - Optical Emission Spectrometry) and recalculated as respectively MgO and CaO. - Particle size analysis: the particles were screened over several sieves, and respective fractions were measured (on weight basis).

- The Hardness (or crushing strength) of the granules is measured using standard testing methods for fertilizer granular hardness. Herein a commercial compression tester (Type Indelco 201-M) is used for measuring the hardness. A sample of the granular product is screened to obtain granules of about 3mm in diameter.

Individual granules are then placed on a flat surface and pressure is applied by a flat- end rod that is attached to the compression tester. The force (expressed in kg) needed to fracture the granule is measured. The reported value is the average of 20 individual granules.

- The wear resistance of the granules is measured as follows: 100 g of the granules without particles less than 0.63 mm are put in a tube (length 40 cm and diameter 4 cm) and tumbled during 1 hour at 40 rpm. 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 wear resistance of the granules (and vice versa).

- The water content is determined gravimetrically by measuring the weight loss of the granules after heating to max. 105°C until a constant weight, for instance by keeping the granules for 1 hour at 105°C or overnight at 80°C, typically in a lab oven.

- Dust can be measured with a commonly used apparatus such as a Heubach dust meter and generally comprises particles smaller than about 10 pm.

[000100] The invention is further described and detailed in the following Examples, which in no way are intended to be limiting.

EXAMPLES

Material preparation

[000101] Spherical granules were prepared with a High Shear Mixer or a rotating disc pelletizer. Briefly, 2000-S000 g of salts were mixed for a few minutes in a Pin Mixer for homogenization of the salts. Feed materials had a particle size below 1000 pm. Materials were then transferred to a rotating disc pelletizer with an angle set somewhere between 40° and 60°. About 10% water was used as binder & added step-wise in a semi-continuous way. In Table 1, the amounts of materials as well as mixing times are summarized. In one of the Examples, molten sulfur (at 140°C) is added. Particles obtained were dried for 4 hours in an oven at 80°C prior to analysis. To determine particle size distribution, particles were sieved (1-4 mm). The analysis results are summarized in Table 2. Examples 1-5

[000102] After drying, the obtained fraction of spherical granules between 1 and 4 mm was up to 75 wt% and more. Hardness could be improved by using a higher percentage of SOP dust (A') as defined. Wear in general was below 10 wt%, and often well below 5 wt%. Also particles based on a blend of SOP and molten S (elemental sulfur) were found to have a good balance of wear and hardness. The use of hot SOP and in particular the use of, in part, the recyclate of a compacted SOP had a positive impact on the granule's hardness.

[000103] All of the particles obtained were free flowing. Table 1: Different test conditions

Table 2: Analysis results

COMPARATIVE EXPERIMENT

[000104] Repeat of the process wherein the feed material comprising potassium sulfate of which the fraction of particles having a size above 1000 miti was too high was found to result in uncontrolled agglomeration and led to the formation of particles having a non-spherical shape. EMBODIMENTS

Further embodiments of the invention are provided below: 1. A process for making a fertilizer in granular form, said process comprising:

(i) Providing a mixture comprising (a) potassium sulfate (A) and (b) one or more binders, said one or more binders including water, wherein at least BO wt.%, preferably at least 40 wt.% of said potassium sulfate (A) has a particle size between 75 and 1000 pm; (ii) Subjecting the mixture to a granulation step to form granules, preferably wherein said granulation step is effected in a wet tumbling granulator; and

(iii) Drying the granules; and

2. The process according to embodiment 1, wherein at least 50 wt.% of said potassium sulfate (A) in the mixture in (i) has a particle size between 75 and 600 pm.

3. The process according to embodiment 1 or 2, wherein at least 90 wt.% of said potassium sulfate (A) in the mixture in (i) has a particle size of no more than 500 pm, preferably no more than 300 pm.

4. The process according to any of the preceding embodiments, wherein said one or more other binders further comprise a hydroxide and/or elemental sulfur (S). 5. The process according to any of the preceding embodiments, wherein at least part of said potassium sulfate (A) is provided in the form a compacted potassium sulfate (A'), preferably wherein at least 10 wt.% of said potassium sulfate (A) is provided in the form a compacted potassium sulfate (A').

6. The process according to embodiment 5, wherein up to 80 wt.% of the potassium sulfate (A) is provided in the form of a compacted potassium sulfate (A').

7. The process according to embodiment 5 or 6, wherein said compacted potassium sulfate (A') has a hardness of at least 2.0 kg, preferably at least 2.5 kg.

8. The process according to any one of embodiments 5 to 7, wherein said compacted potassium sulfate (A') is a recyclate. 9. The process of any of the preceeding embodiments , further comprising at least one of the following steps :

Adding micronutrients and/or elemental sulfur and/or a dye;

Providing one or more coatings;

Rounding the granules; - Glazing and/or oiling and/or waxing the granules.

10. The process of any of any of embodiments 1-9, wherein no rounding of the granules is applied. 11. The process according to any of the preceding embodiments, wherein the mixture further comprises one or more other sulfate salts (B).

12. The process according to embodiment 11, wherein at least BO wt.%, preferably at least 40 wt.% of said one or more other sulfate salts (B) in the mixture in (i) has a particle size between 75 and 1000 pm.

13. The process according to embodiment 11 or 12, wherein at least 50 wt.% of said one or more other sulfate salts (B) in the mixture in (i) has a particle size between 75 and 600 pm.

14. The process according to any one of embodiments 11 to 13, wherein at least 90 wt.% of said one or more other sulfate salts (B) in the mixture in (i) has a particle size of no more than 500 pm, preferably no more than 300 pm.

15. The process according to any preceding embodiment, wherein a granular fertilizer is obtained characterized by the following:

70 wt% or more of the granules have a particle size between 1 and 6 mm, preferably between 2 and 5 mm, more preferably between 2.5 and 4 mm a granule hardness of at least 2 kg, typically at least 2.5 kg, preferably at least 2.7 kg, optionally wherein the granule hardness is less than 5.0 kg; a granule wear of at most 15 wt%, preferably at most 5 wt%, optionally wherein the granule wear is above 0.1 wt.%; a chloride level of at most 10 wt%, preferably at most 5 wt%; and a potassium sulfate content of from 20 to 100 wt%, relative to the total of salts in the fertilizer 16. The process according to embodiment 15, wherein a granular fertilizer is obtained characterized by the following:

70 wt% or more of the granules have a particle size between 2.5 and 4 mm - a granule hardness of at least 2.7 kg a granule wear of at most 5 wt%, a chloride level of at most 5 wt%; and a potassium sulfate content of from 20 to 100 wt%, relative to the total of salts in the fertilizer

17. A granular fertilizer obtainable by a process according to any of the preceding embodiments.

18. A granular fertilizer characterized by the following: - a potassium sulfate content of from 20 to 100 wt%, preferably from 50 to 100 wt%, relative to the total of salts in the fertilizer, a chloride level of at most 10 wt%, preferably at most 5 wt%,

70 wt% or more of the granules have a particle size between 1 and 6 mm, preferably between 2 and 5 mm, more preferably size between 2.5 and 4mm, - a granule hardness of at least 2.7 kg, typically at least 3 kg, , optionally wherein the granule hardness is less than 5.0 kg; and a granule wear of at most 7 wt%, preferably at most 5 wt%, more preferably at most 2 wt%%, optionally wherein the granule wear is above 0.1 wt.%. 19. The granular fertilizer of embodiment 18, further characterized by: a potassium sulfate content of from 50 to 100 wt%, relative to the total of salts in the fertilizer, - a chloride level of at most 5 wt%,

70 wt% or more of the granules have a particle size between 2.5 and 4mm, a granule hardness of at least 3 kg, and a granule wear of at most 2 wt%. 20. The granular fertilizer of embodiment 18, having a granule hardness of at least 2.7 kg, preferably at least 3 kg.

21. The granular fertilizer of any one of embodiments 18 to 20, wherein 90 wt% or more, preferably 95 wt.% or more of the granules have a particle size between 1 and 6 mm, preferably between 1 and 5 mm.

22. The granular fertilizer of any one of embodiments 18 to 21, wherein 90 wt% or more of the granules have a particle size between 2.5 and 4 mm.

23. The granular fertilizer of any of embodiments 18 to 22, wherein less than 1 wt%, preferably less than 0.5 wt% of the granules have a particle size below 1 mm. 24. The granular fertilizer of any one of embodiments 18 to 23, wherein less than 1.5 wt%, preferably less than 1 wt% of the granules have a particle size above 5 mm.

25. The granular fertilizer of any of embodiments 18 to 24, having a d50 of between 3 and 3.5 mm.

26. The granular fertilizer of any of embodiments 18 to 25, wherein 85 wt% or more, preferably 90 wt% or more of the granules have a sphericity of 0.8. 27. The granular fertilizer of any of embodiments 18 to 26, having a potassium level of at least 18 wt%, preferably at least 20 wt%; more preferably at least 25 wt%.

28. The granular fertilizer of any of embodiments 18 to 27, having a potassium level of at least 40 wt%, preferably at least 50 wt%.

29. The granular fertilizer of any of embodiments 18 to 28, having a potassium sulfate content of at least 50 wt%, preferably at least 70 wt%, more preferably at least 90 wt%, relative to the total weight of salts in the fertilizer. 30. The granular fertilizer of any of embodiments 18 to 29, having a porosity as measured with a mercury intrusion process of at least 7 wt%, preferably at least 10 wt%.

31. A solid fertilizer comprising (i) the fertilizer in granular form according to any one of embodiments 18 to 30, and (ii) at least one further solid fertilizer that is different therefrom, for instance such as ammonium nitrate, ammonium sulfate, ammonium phosphate, ammonium diphosphate and/or ureum.

Claims

1. A process for making a fertilizer in granular form, said process comprising: (i) Providing a mixture comprising (a) potassium sulfate (A) and (b) one or more binders, said one or more binders including water, wherein at least 30 wt.%, preferably at least 40 wt.% of said potassium sulfate (A) has a particle size between 75 and 1000 pm;

(iii) Drying the granules; and

2. The process according to claim 1, wherein at least 50 wt.% of said potassium sulfate

(A) in the mixture in (i) has a particle size between 75 and 600 pm.

3. The process according to claim 1 or 2, wherein at least 90 wt.% of said potassium sulfate (A) in the mixture in (i) has a particle size of no more than 500 pm, preferably no more than 300 pm.

4. The process according to any of the preceding claims, wherein said one or more other binders further comprise a hydroxide and/or elemental sulfur (S).

5. The process according to any of the preceding claims, wherein at least part of said potassium sulfate (A) is provided in the form a compacted potassium sulfate (A'), preferably wherein at least 10 wt.% of said potassium sulfate (A) is provided in the form a compacted potassium sulfate (A').

6. The process according to claim 5, wherein up to 80 wt.% of the potassium sulfate (A) is provided in the form of a compacted potassium sulfate (A').

7. The process according to claim 5 or 6, wherein said compacted potassium sulfate (A') has a hardness of at least 3.0 kg, preferably at least 3.5 kg.

8. The process according to any one of claims 5 to 7, wherein said compacted potassium sulfate (A') is a recyclate.

9. The process of any of the preceding claims , further comprising at least one of the following steps :

- Adding micronutrients and/or elemental sulfur and/or a dye;

- Providing one or more coatings;

- Rounding the granules; - Glazing and/or oiling and/or waxing the granules.

10. The process of any of any of claims 1-9, wherein no rounding of the granules is applied.

11. The process according to any of the preceding claims, wherein the mixture further comprises one or more other sulfate salts (B).

12. The process according to claim 11, wherein at least 30 wt.%, preferably at least 40 wt.% of said one or more other sulfate salts (B) in the mixture in (i) has a particle size between 75 and 1000 pm.

13. The process according to claim 11 or 12, wherein at least 50 wt.% of said one or more other sulfate salts (B) in the mixture in (i) has a particle size between 75 and 600 pm.

14. The process according to any one of claims 11 to 13, wherein at least 90 wt.% of said one or more other sulfate salts (B) in the mixture in (i) has a particle size of no more than 500 pm, preferably no more than 300 pm.

15. The process according to any preceding claim, wherein a granular fertilizer is obtained characterized by the following:

70 wt% or more of the granules have a particle size between 1 and 6 mm, preferably between 2 and 5 mm, more preferably between 2.5 and 4 mm a granule hardness of at least 2 kg, typically at least 2.5 kg, preferably at least 2.7 kg; a granule wear of at most 15 wt%, preferably at most 5 wt%; a chloride level of at most 10 wt%, preferably at most 5 wt%; and a potassium sulfate content of from 20 to 100 wt%, relative to the total of salts in the fertilizer

16. The process according to claim 15, wherein a granular fertilizer is obtained characterized by the following:

70 wt% or more of the granules have a particle size between 2.5 and 4 mm a granule hardness of at least 2.7 kg a granule wear of at most 5 wt%, a chloride level of at most 5 wt%; and a potassium sulfate content of from 20 to 100 wt%, relative to the total of salts in the fertilizer

17. A granular fertilizer obtainable by a process according to any of the preceding claims.

18. A granular fertilizer characterized by the following: a potassium sulfate content of from 20 to 100 wt%, preferably from 50 to 100 wt%, relative to the total of salts in the fertilizer, a chloride level of at most 10 wt%, preferably at most 5 wt%,

19. The granular fertilizer of claim 18, further characterized by: a potassium sulfate content of from 50 to 100 wt%, relative to the total of salts in the fertilizer, a chloride level of at most 5 wt%,

70 wt% or more of the granules have a particle size between 2.5 and 4mm, a granule hardness of at least 3 kg, and a granule wear of at most 2 wt%.

20. The granular fertilizer of claim 18, having a granule hardness of at least 2.7 kg, preferably at least 3 kg.

21. The granular fertilizer of any one of claims 18 to 20, wherein 90 wt% or more, preferably 95 wt.% or more of the granules have a particle size between 1 and 6 mm, preferably between 1 and 5 mm.

22. The granular fertilizer of any one of claims 18 to 21, wherein 90 wt% or more of the granules have a particle size between 2.5 and 4 mm.

23. The granular fertilizer of any of claims 18 to 22, wherein less than 1 wt%, preferably less than 0.5 wt% of the granules have a particle size below 1 mm.

24. The granular fertilizer of any one of claims 18 to 23, wherein less than 1.5 wt%, preferably less than 1 wt% of the granules have a particle size above 5 mm.

25. The granular fertilizer of any of claims 18 to 24, having a d50 of between 3 and 3.5 mm.

26. The granular fertilizer of any of claims 18 to 25, wherein 85 wt% or more, preferably 90 wt% or more of the granules have a sphericity of 0.8.

27. The granular fertilizer of any of claims 18 to 26, having a potassium level of at least 18 wt%, preferably at least 20 wt%; more preferably at least 25 wt%.

28. The granular fertilizer of any of claims 18 to 27, having a potassium level of at least 40 wt%, preferably at least 50 wt%.

29. The granular fertilizer of any of claims 18 to 28, having a potassium sulfate content of at least 50 wt%, preferably at least 70 wt%, more preferably at least 90 wt%, relative to the total weight of salts in the fertilizer.

30. The granular fertilizer of any of claims 18 to 29, having a porosity as measured with a mercury intrusion process of at least 7 wt%, preferably at least 10 wt%.

31. A solid fertilizer comprising (i) the fertilizer in granular form according to any one of claims 18 to 30, and (ii) at least one further solid fertilizer that is different therefrom, for instance such as ammonium nitrate, ammonium sulfate, ammonium phosphate, ammonium diphosphate and/or ureum.